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Sorooshian, A, Anderson B, Bauer SE, Braun RA, Cairns B, Crosbie E, Dadashazar H, Diskin G, Ferrare R, Flagan RC, Hair J, Hostetler C, Jonsson HH, Kleb MM, Liu HY, MacDonald AB, McComiskey A, Moore R, Painemal D, Russell LM, Seinfeld JH, Shook M, Smith WL, Thornhill K, Tselioudis G, Wang HL, Zeng XB, Zhang B, Ziemba L, Zuidema P.  2019.  Aerosol-cloud-meteorology interaction airborne field investigations: Using lessons learned from the US West Coast in the design of ACTIVATE off the US East Coast. Bulletin of the American Meteorological Society. 100:1511-1528.   10.1175/bams-d-18-0100.1   AbstractWebsite

We report on a multiyear set of airborne field campaigns (2005-16) off the California coast to examine aerosols, clouds, and meteorology, and how lessons learned tie into the upcoming NASA Earth Venture Suborbital (EVS-3) campaign: Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE; 2019-23). The largest uncertainty in estimating global anthropogenic radiative forcing is associated with the interactions of aerosol particles with clouds, which stems from the variability of cloud systems and the multiple feedbacks that affect and hamper efforts to ascribe changes in cloud properties to aerosol perturbations. While past campaigns have been limited in flight hours and the ability to fly in and around clouds, efforts sponsored by the Office of Naval Research have resulted in 113 single aircraft flights (>500 flight hours) in a fixed region with warm marine boundary layer clouds. All flights used nearly the same payload of instruments on a Twin Otter to fly below, in, and above clouds, producing an unprecedented dataset. We provide here i) an overview of statistics of aerosol, cloud, and meteorological conditions encountered in those campaigns and ii) quantification of model-relevant metrics associated with aerosol-cloud interactions leveraging the high data volume and statistics. Based on lessons learned from those flights, we describe the pragmatic innovation in sampling strategy (dual-aircraft approach with combined in situ and remote sensing) that will be used in ACTIVATE to generate a dataset that can advance scientific understanding and improve physical parameterizations for Earth system and weather forecasting models, and for assessing next-generation remote sensing retrieval algorithms.

Lee, AKY, Rivellini LH, Chen CL, Liu J, Price DJ, Betha R, Russell LM, Zhang XL, Cappa CD.  2019.  Influences of primary emission and secondary coating formation on the particle diversity and mixing state of black carbon particles. Environmental Science & Technology. 53:9429-9438.   10.1021/acs.est.9b03064   AbstractWebsite

The mixing state of black carbon (BC) affects its environmental fate and impacts. This work investigates particle diversity and mixing state for refractory BC (rBC) containing particles in an urban environment. The chemical compositions of individual rBC-containing particles were measured, from which a mixing state index and particle diversity were determined. The mixing state index (X) varied between 26% and 69% with the average of 48% in this study and was slightly enhanced with the photochemical age of air masses, indicating that most of the rBC-containing particles cannot be simply explained by fully externally and internally mixed model. Clustering of single particle measurements was used to investigate the potential effects of different primary emissions and atmospheric processes on rBC-containing particle diversity and mixing state. The average particle species diversity and the bulk population species diversity both increased with primary traffic emissions and elevated nitrate concentrations in the morning but gradually decreased with secondary organic aerosol (SOA) formation in the afternoon. The single particle clustering results illustrate that primary traffic emissions and entrainment of nitrate-containing rBC particles from the residual layer to the surface could lead to more heterogeneous aerosol compositions, whereas substantial fresh SOA formation near vehicular emissions made the rBC-containing particles more homogeneous. This work highlights the importance of considering particle diversity and mixing state for investigating the chemical evolution of rBC-containing particles and the potential effects of coating on BC absorption enhancement.

Behrenfeld, MJ, Moore RH, Hostetler CA, Graff J, Gaube P, Russell LM, Chen G, Doney SC, Giovannoni S, Liu HY, Proctor C, Bolalios LM, Baetge N, Davie-Martin C, Westberry TK, Bates TS, Bell TG, Bidle KD, Boss ES, Brooks SD, Cairns B, Carlson C, Halsey K, Harvey EL, Hu CM, Karp-Boss L, Kleb M, Menden-Deuer S, Morison F, Quinn PK, Scarino AJ, Anderson B, Chowdhary J, Crosbie E, Ferrare R, Haire JW, Hu YX, Janz S, Redemann J, Saltzman E, Shook M, Siegel DA, Wisthaler A, Martine MY, Ziemba L.  2019.  The North Atlantic Aerosol and Marine Ecosystem Study (NAAMES): Science motive and mission overview. Frontiers in Marine Science. 6   10.3389/fmars.2019.00122   AbstractWebsite

The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) is an interdisciplinary investigation to improve understanding of Earth's ocean ecosystem-aerosol-cloud system. Specific overarching science objectives for NAAMES are to (1) characterize plankton ecosystem properties during primary phases of the annual cycle and their dependence on environmental forcings, (2) determine how these phases interact to recreate each year the conditions for an annual plankton bloom, and (3) resolve how remote marine aerosols and boundary layer clouds are influenced by plankton ecosystems. Four NAAMES field campaigns were conducted in the western subarctic Atlantic between November 2015 and April 2018, with each campaign targeting specific seasonal events in the annual plankton cycle. A broad diversity of measurements were collected during each campaign, including ship, aircraft, autonomous float and drifter, and satellite observations. Here, we present an overview of NAAMES science motives, experimental design, and measurements. We then briefly describe conditions and accomplishments during each of the four field campaigns and provide information on how to access NAAMES data. The intent of this manuscript is to familiarize the broad scientific community with NAAMES and to provide a common reference overview of the project for upcoming publications.

Chen, SJ, Russell LM, Cappa CD, Zhang XL, Kleeman MJ, Kumar A, Liu D, Ramanathana V.  2019.  Comparing black and brown carbon absorption from AERONET and surface measurements at wintertime Fresno. Atmospheric Environment. 199:164-176.   10.1016/j.atmosenv.2018.11.032   AbstractWebsite

The radiative impacts of black carbon (BC) and brown carbon (BrC) are widely recognized but remain highly uncertain. The Aerosol Robotic Network (AERONET) provides measurements of aerosol optical depth (AOD), aerosol absorption optical depth (AAOD), and other parameters. AERONET AAOD measurements have been used to estimate the relative contributions of BC and BrC to the total absorption at select sites and have the potential to be used across the global network, but the accuracy of the partitioning method has not been established and the uncertainties not characterized. We made surface-level measurements of aerosol optical properties from January 13 to February 10, 2013, and from December 25, 2014, to January 13, 2015, at Fresno, California. The contribution of BrC and BC to the absorption at 405 nm was estimated from the surface-level measurements using a combined mass absorption coefficient and thermodenuder method. The surface-level measurements were compared with BC and BrC absorption at 440 nm estimated from AERONET measurements of the absolute AAOD and the absorption angstrom ngstrom exponent (AERONET-AAE method). In 2013, AERONET results showed that BC and BrC contributed 67% and 33%, respectively, of absorption at 440 nm while the surface-level measurements showed that BC and BrC contributed 89% and 11%, respectively, of absorption at 405 nm. In 2014, AERONET results showed BC and BrC absorption were 72% and 28%, respectively, and the BC and BrC surface measurements were 68% and 32%, respectively. The boundary layer conditions showed that the comparison between AERONET measurements and surface-based estimates was more appropriate in 2014 than in 2013. As a result, AERONET measurements and surface-based estimates had strong or moderate correlations and slopes near unity in 2014. Thus, surface measurements were more representative of column BC and BrC absorption in 2014.

Cappa, CD, Zhang XL, Russell LM, Collier S, Lee AKY, Chen CL, Betha R, Chen SJ, Liu J, Price DJ, Sanchez KJ, McMeeking GR, Williams LR, Onasch TB, Worsnop DR, Abbatt J, Zhang Q.  2019.  Light absorption by ambient black and brown carbon and its dependence on black carbon coating state for two California, USA, cities in winter and summer. Journal of Geophysical Research-Atmospheres. 124:1550-1577.   10.1029/2018jd029501   AbstractWebsite

Observations from a wintertime and summertime field campaign are used to assess the relationship between black and brown carbon (BC and BrC, respectively) optical properties and particle composition and coating state. The wintertime campaign, in Fresno, CA, was impacted by primary emissions from residential wood burning, secondary organic and inorganic particle formation, and BC from motor vehicles. Two major types of BrC were observed in wintertime. One occurred primarily at nightthe result of primary biomass burning emissions. The second was enhanced in daytime and strongly associated with particulate nitrate and the occurrence of fog. The biomass-burning-derived BrC absorbed more strongly than the nitrate-associated BrC but had a weaker wavelength dependence. The wintertime BC-specific mass absorption coefficient (MAC(BC)) exhibited limited dependence on the ensemble-average coating-to-BC mass ratio (Rcoat-rBC) at all wavelengths, even up to Rcoat-rBC of similar to 5. For the summertime campaign, in Fontana, CA, BC dominated the light absorption, with negligible BrC contribution even after substantial photochemical processing. The summertime MAC(BC) exhibited limited dependence on Rcoat-rBC, even up to ratios of >10. Based on the four classes of BC-containing particles identified by Lee et al. (2017, ) for the summertime measurements, the general lack of an absorption enhancement can be partlyalthough not entirelyattributed to an unequal distribution of coating materials between the BC-containing particle types. These observations demonstrate that in relatively near-source environments, even those impacted by strong secondary aerosol production, the ensemble-average, mixing-induced absorption enhancement for BC due to coatings can be quite small. Plain Language Summary Particles in the atmosphere can scatter light, which has a cooling effect, or absorb light, which can contribute to localized atmospheric warming. Black carbon is a highly absorbing yet short-lived climate pollutant that when coated with other materials can in theory have enhanced absorption. Organic compounds in particles can also absorb light, although tend to absorb less strongly than black carbon. Absorbing organic compounds are collectively referred to as brown carbon. We measured the composition and light absorption properties of atmospheric particles in wintertime Fresno, CA, and summertime Fontana, CA. In Fresno, we found two types of brown carbon contributed significantly to the overall light absorption by particles, in addition to absorption by black carbon. One of the brown carbon aerosol types in Fresno was emitted during wood burning, and the other was produced from chemical reactions in the atmosphere. In summertime Fontana, black carbon particles dominated the light absorption, with little contribution from brown carbon. Overall, at both sites the coating of materials onto black carbon particles had a limited impact on the absorption by black carbon, except to the extent that the materials themselves were absorbing.

Abbatt, JPD, Leaitch WR, Aliabadi AA, Bertram AK, Blanchet JP, Boivin-Rioux A, Bozem H, Burkart J, Chang RYW, Charette J, Chaubey JP, Christensen RJ, Cirisan A, Collins DB, Croft B, Dionne J, Evans GJ, Fletcher CG, Gali M, Ghahremaninezhad R, Girard E, Gong WM, Gosselin M, Gourdal M, Hanna SJ, Hayashida H, Herber AB, Hesaraki S, Hoor P, Huang L, Hussherr R, Irish VE, Keita SA, Kodros JK, Kollner F, Kolonjari F, Kunkel D, Ladino LA, Law K, Levasseur M, Libois Q, Liggio J, Lizotte M, Macdonald KM, Mahmood R, Martin RV, Mason RH, Miller LA, Moravek A, Mortenson E, Mungall EL, Murphy JG, Namazi M, Norman AL, O'Neill NT, Pierce JR, Russell LM, Schneider J, Schulz H, Sharma S, Si M, Staebler RM, Steiner NS, Thomas JL, Von Salzen K, Wentzell JJB, Willis MD, Wentworth GR, Xu JW, Yakobi-Hancock JD.  2019.  Overview paper: New insights into aerosol and climate in the Arctic. Atmospheric Chemistry and Physics. 19:2527-2560.   10.5194/acp-19-2527-2019   AbstractWebsite

Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as they relate to climate forcing. The overall goal of NETCARE research has been to use an interdisciplinary approach encompassing extensive field observations and a range of chemical transport, earth system, and biogeochemical models. Several major findings and advances have emerged from NETCARE since its formation in 2013. (1) Unexpectedly high summertime dimethyl sulfide (DMS) levels were identified in ocean water (up to 75 nM) and the overlying atmosphere (up to 1 ppbv) in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds, which are widely prevalent, were identified as an important DMS source (with DMS concentrations of up to 6nM and a potential contribution to atmospheric DMS of 20% in the study area). (2) Evidence of widespread particle nucleation and growth in the marine boundary layer was found in the CAA in the summertime, with these events observed on 41% of days in a 2016 cruise. As well, at Alert, Nunavut, particles that are newly formed and grown under conditions of minimal anthropogenic influence during the months of July and August are estimated to contribute 20% to 80% of the 30-50 nm particle number density. DMS-oxidation-driven nucleation is facilitated by the presence of atmospheric ammonia arising from seabird-colony emissions, and potentially also from coastal regions, tundra, and biomass burning. Via accumulation of secondary organic aerosol (SOA), a significant fraction of the new particles grow to sizes that are active in cloud droplet formation. Although the gaseous precursors to Arctic marine SOA remain poorly defined, the measured levels of common continental SOA precursors (isoprene and monoterpenes) were low, whereas elevated mixing ratios of oxygenated volatile organic compounds (OVOCs) were inferred to arise via processes involving the sea surface microlayer. (3) The variability in the vertical distribution of black carbon (BC) under both springtime Arctic haze and more pristine summertime aerosol conditions was observed. Measured particle size distributions and mixing states were used to constrain, for the first time, calculations of aerosol-climate interactions under Arctic conditions. Aircraft- and ground-based measurements were used to better establish the BC source regions that supply the Arctic via long-range transport mechanisms, with evidence for a dominant springtime contribution from eastern and southern Asia to the middle troposphere, and a major contribution from northern Asia to the surface. (4) Measurements of ice nucleating particles (INPs) in the Arctic indicate that a major source of these particles is mineral dust, likely derived from local sources in the summer and long-range transport in the spring. In addition, INPs are abundant in the sea surface microlayer in the Arctic, and possibly play a role in ice nucleation in the atmosphere when mineral dust concentrations are low. (5) Amongst multiple aerosol components, BC was observed to have the smallest effective deposition velocities to high Arctic snow (0.03 cm s(-1)).

Mulmenstadt, J, Sourdeval O, Henderson DS, L'Ecuyer TS, Unglaub C, Jungandreas L, Bohm C, Russell LM, Quaas J.  2018.  Using CALIOP to estimate cloud-field base height and its uncertainty: the Cloud Base Altitude Spatial Extrapolator (CBASE) algorithm and datasety. Earth System Science Data. 10:2279-2293.   10.5194/essd-10-2279-2018   AbstractWebsite

A technique is presented that uses attenuated backscatter profiles from the CALIOP satellite lidar to estimate cloud base heights of lower-troposphere liquid clouds (cloud base height below approximately 3 km). Even when clouds are thick enough to attenuate the lidar beam (optical thickness tau greater than or similar to 5), the technique provides cloud base heights by treating the cloud base height of nearby thinner clouds as representative of the surrounding cloud field. Using ground-based ceilometer data, uncertainty estimates for the cloud base height product at retrieval resolution are derived as a function of various properties of the CALIOP lidar profiles. Evaluation of the predicted cloud base heights and their predicted uncertainty using a second statistically independent ceilometer dataset shows that cloud base heights and uncertainties are biased by less than 10 %. Geographic distributions of cloud base height and its uncertainty are presented. In some regions, the uncertainty is found to be substantially smaller than the 480 m uncertainty assumed in the A-Train surface downwelling longwave estimate, potentially permitting the most uncertain of the radiative fluxes in the climate system to be better constrained.

Betha, R, Russell LM, Chen CL, Liu J, Price DJ, Sanchez KJ, Chen SJ, Lee AKY, Collier SC, Zhang Q, Zhang XL, Cappa CD.  2018.  Larger submicron particles for emissions with residential burning in wintertime San Joaquin Valley (Fresno) than for vehicle combustion in summertime South Coast Air Basin (Fontana). Journal of Geophysical Research-Atmospheres. 123:10526-10545.   10.1029/2017jd026730   AbstractWebsite

Size-resolved composition of atmospheric aerosol particles during winter (19 December 2014 to 13 January 2015) in the San Joaquin Valley at Fresno and during summer (4 to 28 July 2015) in the Southern California Air Basin at Fontana were measured by aerosol mass spectrometer, Fourier transform infrared spectrometer, single particle soot photometer, and scanning electrical mobility sizer. The Fresno study had low-fog and high-fog winter conditions, and residential burning was a frequent contributor to evening emissions. Fireworks during Fourth of July celebrations characterized the start of the Fontana study; the remaining days were categorized as nonfirework days and were mostly affected by traffic emissions. Fresno had particle distributions with number mode diameters of 70-150 nm, and Fontana had 30-50-nm diameters. The nonrefractory organic mass mode diameters were also larger at Fresno (250-380 nm in dry mobility diameter) than at Fontana (130-150 nm, 280 nm in dry mobility diameter) as were refractory black carbon particles (Fresno: 80-180 nm; Fontana: 80-100 nm in dry volume equivalent diameter). The size dependence of organic contributions to particle mass indicated that condensation or other surface-limited processes contributed oxidized organic fractions to aerosol mass in Fontana but that volume-limited aqueous reactions produced organic mass on both low-fog and high-fog days in Fresno. Linear regression analysis of organic aerosol sources with size-resolved particle volume at different times of day also showed that residential burning-related particles increased from 70-160 nm in the evening (18:00 to 23:59) to 150-260 nm at night (00:00 to 05:59) on low-fog days.

Chen, CL, Chen SJ, Russell LM, Liu J, Price DJ, Betha R, Sanchez KJ, Lee AKY, Williams L, Collier SC, Zhang Q, Kumar A, Kleeman MJ, Zhang XL, Cappa CD.  2018.  Organic aerosol particle chemical properties associated with residential burning and fog in wintertime San Joaquin Valley (Fresno) and with vehicle and firework emissions in summertime South Coast Air Basin (Fontana). Journal of Geophysical Research-Atmospheres. 123:10707-10731.   10.1029/2018jd028374   AbstractWebsite

Organic aerosol mass (OM) components were investigated at Fresno in winter and at Fontana in summer by positive matrix factorization of high-resolution time-of-flight aerosol mass spectra and of Fourier Transform infrared spectra, as well as by k-means clustering of light-scattering (LS) aerosol single-particle spectra. The results were comparable for all three methods at both sites, showing different contributions of primary and secondary organic aerosol sources to PM1. At Fresno biomass burning organic aerosol contributed 27% of OM on low-fog days, and nitrate-related oxidized OA (NOOA) accounted for 47% of OM on high-fog days, whereas at Fontana very oxygenated organic aerosol (VOOA) components contributed 58-69% of OM. Amine and organosulfate fragment concentrations were between 2 and 3 times higher on high-fog days than on low-fog days at Fresno, indicating increased formation from fog-related processes. NOOA and biomass burning organic aerosol components were largely on different particles than the VOOA components in Fresno, but in Fontana both NOOA and VOOA components were distributed on most particle types, consistent with a longer time for and a larger contribution from gas-phase photochemical secondary organic aerosol formation in summer Fontana than winter Fresno. Uncommon trace organic fragments, elevated inorganic, and alcohol group submicron mass concentrations persisted at Fontana for more than 5days after 4 July fireworks. These unique aerosol chemical compositions at Fresno and Fontana show substantial and extended air-quality impacts from residential burning and fireworks.

Liu, J, Russell LM, Ruggeri G, Takahama S, Claflin MS, Ziemann PJ, Pye HOT, Murphy BN, Xu L, Ng NL, McKinney KA, Budisulistiorini SH, Bertram TH, Nenes A, Surratt JD.  2018.  Regional similarities and NOx-related increases in biogenic secondary organic aerosol in summertime southeastern United States. Journal of Geophysical Research-Atmospheres. 123:10620-10636.   10.1029/2018jd028491   AbstractWebsite

During the 2013 Southern Oxidant and Aerosol Study, Fourier transform infrared spectroscopy (FTIR) and aerosol mass spectrometer (AMS) measurements of submicron mass were collected at Look Rock (LRK), Tennessee, and Centreville (CTR), Alabama. Carbon monoxide and submicron sulfate and organic mass concentrations were 15-60% higher at CTR than at LRK, but their time series had moderate correlations (r similar to 0.5). However, NOx had no correlation (r=0.08) between the two sites with nighttime-to-early-morning peaks 3-10 times higher at CTR than at LRK. Organic mass (OM) sources identified by FTIR Positive Matrix Factorization (PMF) had three very similar factors at both sites: fossil fuel combustion-related organic aerosols, mixed organic aerosols, and biogenic organic aerosols (BOA). The BOA spectrum from FTIR is similar (cosine similarity>0.6) to that of lab-generated particle mass from the photochemical oxidation of both isoprene and monoterpenes under high NOx conditions from chamber experiments. The BOA mass fraction was highest during the night at CTR but in the afternoon at LRK. AMS PMF resulted in two similar pairs of factors at both sites and a third nighttime NOx-related factor (33% of OM) at CTR but a daytime nitrate-related factor (28% of OM) at LRK. NOx was correlated with BOA and LO-OOA for NOx concentrations higher than 1ppb at both sites, producing 0.5 +/- 0.1 mu g/m(3) for CTR-LO-OOA and 1.0 +/- 0.3 mu g/m(3) for CTR-BOA additional biogenic OM for each 1ppb increase of NOx.

Elliott, S, Burrows S, Cameron-Smith P, Hoffman F, Hunke E, Jeffery N, Liu YN, Maltrud M, Menzo Z, Ogunro O, Van Roekel L, Wang SL, Brunke M, Jin MB, Letscher R, Meskhidze N, Russell L, Simpson I, Stokes D, Wingenter O.  2018.  Does marine surface tension have global biogeography? Addition for the OCEANFILMS package Atmosphere. 9   10.3390/atmos9060216   AbstractWebsite

We apply principles of Gibbs phase plane chemistry across the entire ocean-atmosphere interface to investigate aerosol generation and geophysical transfer issues. Marine surface tension differences comprise a tangential pressure field controlling trace gas fluxes, primary organic inputs, and sea spray salt injections, in addition to heat and momentum fluxes. Mapping follows from the organic microlayer composition, now represented in ocean system models. Organic functional variations drive the microforcing, leading to (1) reduced turbulence and (by extension) laminar gas-energy diffusion; plus (2) altered bubble film mass emission into the boundary layer. Interfacial chemical behaviors are, therefore, closely reviewed as the background. We focus on phase transitions among two dimensional "solid, liquid, and gaseous" states serving as elasticity indicators. From the pool of dissolved organic carbon (DOC) only proteins and lipids appear to occupy significant atmospheric interfacial areas. The literature suggests albumin and stearic acid as the best proxies, and we distribute them through ecodynamic simulation. Consensus bulk distributions are obtained to control their adsorptive equilibria. We devise parameterizations for both the planar free energy and equation of state, relating excess coverage to the surface pressure and its modulus. Constant settings for the molecular surrogates are drawn from laboratory study and successfully reproduce surfactant solid-to-gas occurrence in compression experiments. Since DOC functionality measurements are rare, we group them into super-ecological province tables to verify aqueous concentration estimates. Outputs are then fed into a coverage, tension, elasticity code. The resulting two dimensional pressure contours cross a critical range for the regulation of precursor piston velocity, bubble breakage, and primary aerosol sources plus ripple damping. Concepts extend the water-air adsorption theory currently embodied in our OCEANFILMS aerosol emissions package, and the two approaches could be inserted into Earth System Models together. Uncertainties in the logic include kinetic and thermochemical factors operating at multiple scales.

Liu, J, Dedrick J, Russell LM, Senum GI, Uin J, Kuang CG, Springston SR, Leaitch WR, Aiken AC, Lubin D.  2018.  High summertime aerosol organic functional group concentrations from marine and seabird sources at Ross Island, Antarctica, during AWARE. Atmospheric Chemistry and Physics. 18:8571-8587.   10.5194/acp-18-8571-2018   AbstractWebsite

Observations of the organic components of the natural aerosol are scarce in Antarctica, which limits our understanding of natural aerosols and their connection to seasonal and spatial patterns of cloud albedo in the region. From November 2015 to December 2016, the ARM West Antarctic Radiation Experiment (AWARE) measured submicron aerosol properties near McMurdo Station at the southern tip of Ross Island. Submicron organic mass (OM), particle number, and cloud condensation nuclei concentrations were higher in summer than other seasons. The measurements included a range of compositions and concentrations that likely reflected both local anthropogenic emissions and natural background sources. We isolated the natural organic components by separating a natural factor and a local combustion factor. The natural OM was 150 times higher in summer than in winter. The local anthropogenic emissions were not hygroscopic and had little contribution to the CCN concentrations. Natural sources that included marine sea spray and seabird emissions contributed 56 % OM in summer but only 3 % in winter. The natural OM had high hydroxyl group fraction (55 %), 6 % alkane, and 6 % amine group mass, consistent with marine organic composition. In addition, the Fourier transform infrared (FTIR) spectra showed the natural sources of organic aerosol were characterized by amide group absorption, which may be from seabird populations. Carboxylic acid group contributions were high in summer and associated with natural sources, likely forming by secondary reactions.

Collier, S, Williams LR, Onasch TB, Cappa CD, Zhang XL, Russell LM, Chen CL, Sanchez KJ, Worsnop DR, Zhang Q.  2018.  Influence of emissions and aqueous processing on particles containing black carbon in a polluted urban environment: Insights from a soot particle-aerosol mass spectrometer. Journal of Geophysical Research-Atmospheres. 123:6648-6666.   10.1002/2017jd027851   AbstractWebsite

Inorganic and organic coatings on black carbon (BC) particles can enhance light absorption and affect atmospheric lifetimes of BC-containing particles and thus have significant implications for climate. To study the physical and chemical characteristics of atmospheric BC and BC-associated coatings, a soot particle-aerosol mass spectrometer was deployed during the winter of 2014-2015 in Fresno, a city located in the San Joaquin Valley of California, to selectively analyze BC-containing particles. Comparing soot particle-aerosol mass spectrometer measurements to those from the collocated single-particle soot photometer (SP2) and high-resolution aerosol mass spectrometer, we found that 17% of total submicrometer aerosol mass was associated with BC-containing particles, suggesting that a majority of the fine particles in Fresno contained no BC. Most BC-containing particles appeared to be associated with residential wood burning and vehicular traffic. These particles typically had a bulk-average mass ratio of coating to BC (R-coat/rBC) less than 2. However, during periods of persistent fog larger R-coat/rBC values were observed, with the coatings primarily composed of secondary inorganic and organic components that likely resulted from aqueous-phase processing. Specifically, compared to periods with less fog, the BC coating increased in concentration and contained a larger fraction of nitrate and oxidized organic matter. The size distributions of BC and associated organic coating were generally centered around 300nm in vacuum aerodynamic diameter. However, during foggy periods BC had an additional peak at 400nm and organics and nitrate displayed a prominent mode in the accumulation size range. Plain Language Summary Various combustion processes can emit soot, or black carbon (BC), particles with properties highly relevant to climate change and respiratory health. Often, BC particles are coated with other materials derived from the same combustion source or added in the atmosphere as these particles age. This coating material can have profound effects on the behavior, properties, and longevity of BC. In this study we deployed an instrument called a soot particle-aerosol mass spectrometer to selectively analyze particles containing BC and investigate their coating, concentration, and composition in real time in Fresno, CA, in wintertime. The properties of BC particles were found to be mainly controlled by emission sources but were also significantly influenced by humid meteorological conditions.

Leaitch, WR, Russell LM, Liu J, Kolonjari F, Toom D, Huang L, Sharma S, Chivulescu A, Veber D, Zhang WD.  2018.  Organic functional groups in the submicron aerosol at 82.5 degrees N, 62.5 degrees W from 2012 to 2014. Atmospheric Chemistry and Physics. 18:3269-3287.   10.5194/acp-18-3269-2018   AbstractWebsite

The first multi-year contributions from organic functional groups to the Arctic submicron aerosol are documented using 126 weekly-integrated samples collected from April 2012 to October 2014 at the Alert Observatory (82.45 degrees N, 62.51 degrees W). Results from the particle transport model FLEXPART, linear regressions among the organic and inorganic components and positive matrix factorization (PMF) enable associations of organic aerosol components with source types and regions. Lower organic mass ( OM) concentrations but higher ratios of OM to non-sea-salt sulfate mass concentrations (nss-SO4=) accompany smaller particles during the summer (JJA). Conversely, higher OM but lower OM / nss-SO4= 4 accompany larger particles during winter-spring. OM ranges from 7 to 460 ng m(-3), and the study average is 129 ng m(-3). The monthly maximum in OM occurs during May, 1 month after the peak in nss-SO4= and 2 months after that of elemental carbon (EC). Winter (DJF), spring (MAM), summer and fall (SON) values of OM / nss-SO4= are 26, 28, 107 and 39%, respectively, and overall about 40% of the weekly variability in the OM is associated with nss-SO4=. Respective study-averaged concentrations of alkane, alcohol, acid, amine and carbonyl groups are 57, 24, 23, 15 and 11 ng m(-3), representing 42, 22, 18, 14 and 5% of the OM, respectively. Carbonyl groups, detected mostly during spring, may have a connection with snow chemistry. The seasonally highest O/C occurs during winter (0.85) and the lowest O/C is during spring (0.51); increases in O/C are largely due to increases in alcohol groups. During winter, more than 50% of the alcohol groups are associated with primary marine emissions, consistent with Shaw et al. (2010) and Frossard et al. (2011). A secondary marine connection, rather than a primary source, is suggested for the highest and most persistent O/C observed during the coolest and cleanest summer (2013), when alcohol and acid groups made up 63% of the OM. A secondary marine source may be a general feature of the summer OM, but higher contributions from alkane groups to OM during the warmer summers of 2012 (53%) and 2014 (50%) were likely due to increased contributions from combustion sources. Evidence for significant contributions from biomass burning (BB) was present in 4% of the weeks. During the dark months (NDJF), 29, 28 and 14% of the nss-SO4=, EC and OM were associated with transport times over the gas flaring region of northern Russia and other parts of Eurasia. During spring, those percentages dropped to 11% for each of nss-SO4= and EC values, respectively, and there is no association of OM. Large percentages of the Arctic haze characterized at Alert likely have origins farther than 10 days of transport time and may be from outside of the Eurasian region. Possible sources of unusually high nss-SO4= and OM during September-October 2014 are volcanic emissions or the "Smoking Hills"' area of the Northwest Territories, Canada.

Sanchez, KJ, Chen CL, Russell LM, Betha R, Liu J, Price DJ, Massoli P, Ziemba LD, Crosbie EC, Moore RH, Muller M, Schiller SA, Wisthaler A, Lee AKY, Quinn PK, Bates TS, Porter J, Bell TG, Saltzman ES, Vaillancourt RD, Behrenfeld MJ.  2018.  Substantial seasonal contribution of observed biogenic sulfate particles to cloud condensation nuclei. Scientific Reports. 8   10.1038/s41598-018-21590-9   AbstractWebsite

Biogenic sources contribute to cloud condensation nuclei (CCN) in the clean marine atmosphere, but few measurements exist to constrain climate model simulations of their importance. The chemical composition of individual atmospheric aerosol particles showed two types of sulfate-containing particles in clean marine air masses in addition to mass-based Estimated Salt particles. Both types of sulfate particles lack combustion tracers and correlate, for some conditions, to atmospheric or seawater dimethyl sulfide (DMS) concentrations, which means their source was largely biogenic. The first type is identified as New Sulfate because their large sulfate mass fraction (63% sulfate) and association with entrainment conditions means they could have formed by nucleation in the free troposphere. The second type is Added Sulfate particles (38% sulfate), because they are preexisting particles onto which additional sulfate condensed. New Sulfate particles accounted for 31% (7 cm(-3)) and 33% (36 cm(-3)) CCN at 0.1% supersaturation in late-autumn and late-spring, respectively, whereas sea spray provided 55% (13 cm(-3)) in late-autumn but only 4% (4 cm(-3)) in late-spring. Our results show a clear seasonal difference in the marine CCN budget, which illustrates how important phytoplankton-produced DMS emissions are for CCN in the North Atlantic.

Lee, AKY, Chen CL, Liu J, Price DJ, Betha R, Russell LM, Zhang XL, Cappa CD.  2017.  Formation of secondary organic aerosol coating on black carbon particles near vehicular emissions. Atmospheric Chemistry and Physics. 17:15055-15067.   10.5194/acp-17-15055-2017   AbstractWebsite

Black carbon (BC) emitted from incomplete combustion can result in significant impacts on air quality and climate. Understanding the mixing state of ambient BC and the chemical characteristics of its associated coatings is particularly important to evaluate BC fate and environmental impacts. In this study, we investigate the formation of organic coatings on BC particles in an urban environment (Fontana, California) under hot and dry conditions using a soot-particle aerosol mass spectrometer (SP-AMS). The SP-AMS was operated in a configuration that can exclusively detect refractory BC (rBC) particles and their coatings. Using the log(NOx / NOy) ratio as a proxy for photochemical age of air masses, substantial formation of secondary organic aerosol (SOA) coatings on rBC particles was observed due to active photochemistry in the afternoon, whereas primary organic aerosol (POA) components were strongly associated with rBC from fresh vehicular emissions in the morning rush hours. There is also evidence that cooking-related organic aerosols were externally mixed from rBC. Positive matrix factorization and elemental analysis illustrate that most of the observed SOA coatings were freshly formed, providing an opportunity to examine SOA coating formation on rBCs near vehicular emissions. Approximately 7-20 wt% of secondary organic and inorganic species were estimated to be internally mixed with rBC on average, implying that rBC is unlikely the major condensation sink of SOA in this study. Comparison of our results to a co-located standard high-resolution time-off-light aerosol mass spectrometer (HR-ToF-AMS) measurement suggests that at least a portion of SOA materials con-densed on rBC surfaces were chemically different from oxygenated organic aerosol (OOA) particles that were externally mixed with rBC, although they could both be generated from local photochemistry.

Keene, WC, Long MS, Reid JS, Frossard AA, Kieber DJ, Maben JR, Russell LM, Kinsey JD, Quinn PK, Bates TS.  2017.  Factors that modulate properties of primary marine aerosol generated from ambient seawater on ships at sea. Journal of Geophysical Research-Atmospheres. 122:11961-11990.   10.1002/2017jd026872   AbstractWebsite

Model primary marine aerosol (mPMA) was produced by bubbling clean air through flowing natural seawater in a high-capacity generator deployed on ships in the eastern North Pacific and western North Atlantic Oceans. Physicochemical properties of seawater and mPMA were quantified to characterize factors that modulated production. Differences in surfactant organic matter (OM) and associated properties including surface tension sustained plumes with smaller bubble sizes, slower rise velocities, larger void fractions, and older surface ages in biologically productive relative to oligotrophic seawater. Production efficiencies for mPMA number (PEnum) and mass (PEmass) per unit air detrained from biologically productive seawater during daytime were greater and mass median diameters smaller than those in the same seawater at night and in oligotrophic seawater during day and night. PEmass decreased with increasing air detrainment rate suggesting that surface bubble rafts suppressed emission of jet droplets and associated mPMA mass. Relative to bubbles emitted at 60 cm depth, PEnum for bubbles emitted from 100 cm depth was approximately 2 times greater. mPMA OM enrichment factors (EFs) and mass fractions based on a coarse frit, fine frits, and a seawater jet exhibited similar size-dependent variability over a wide range in chlorophyll a concentrations. Results indicate that the physical production of PMA number and mass from the ocean surface varies systematically as interrelated functions of seawater type and, in biologically productive waters, time of day; bubble injection rate, depth, size, and surface age; and physical characteristics of the air-water interface whereas size-resolved OM EFs and mass fractions are relatively invariant.

Murphy, BN, Woody MC, Jimenez JL, Carlton AMG, Hayes PL, Liu S, Ng NL, Russell LM, Setyan A, Xu L, Young J, Zaveri RA, Zhang Q, Pye HOT.  2017.  Semivolatile POA and parameterized total combustion SOA in CMAQv5.2: impacts on source strength and partitioning. Atmospheric Chemistry and Physics. 17:11107-11133.   10.5194/acp-17-11107-2017   AbstractWebsite

Mounting evidence from field and laboratory observations coupled with atmospheric model analyses shows that primary combustion emissions of organic compounds dynamically partition between the vapor and particulate phases, especially as near-source emissions dilute and cool to ambient conditions. The most recent version of the Community Multiscale Air Quality model version 5.2 (CMAQv5.2) accounts for the semivolatile partitioning and gas-phase aging of these primary organic aerosol (POA) compounds consistent with experimentally derived parameterizations. We also include a new surrogate species, potential secondary organic aerosol from combustion emissions (pcSOA), which provides a representation of the secondary organic aerosol (SOA) from anthropogenic combustion sources that could be missing from current chemical transport model predictions. The reasons for this missing mass likely include the following: (1) unspeciated semivolatile and intermediate volatility organic compound (SVOC and IVOC, respectively) emissions missing from current inventories, (2) multigenerational aging of organic vapor products from known SOA precur-sors (e.g., toluene, alkanes), (3) underestimation of SOA yields due to vapor wall losses in smog chamber experiments, and (4) reversible organic compounds-water interactions and/or aqueous-phase processing of known organic vapor emissions. CMAQ predicts the spatially averaged contribution of pcSOA to OA surface concentrations in the continental United States to be 38.6 and 23.6% in the 2011 winter and summer, respectively. Whereas many past modeling studies focused on a particular measurement campaign, season, location, or model configuration, we endeavor to evaluate the model and important uncertain parameters with a comprehensive set of United States-based model runs using multiple horizontal scales (4 and 12 km), gas-phase chemical mechanisms, and seasons and years. The model with representation of semivolatile POA improves predictions of hourly OA observations over the traditional nonvolatile model at sites during field campaigns in southern California (CalNex, May-June 2010), northern California (CARES, June 2010), the southeast US (SOAS, June 2013; SEARCH, January and July, 2011). Model improvements manifest better correlations (e.g., the correlation coefficient at Pasadena at night increases from 0.38 to 0.62) and reductions in underprediction during the photochemically active afternoon period (e.g., bias at Pasadena from -5.62 to -2.42 mu gm(-3)). Daily averaged predictions of observations at routine-monitoring networks from simulations over the continental US (CONUS) in 2011 show modest improvement during winter, with mean biases reducing from 1.14 to 0.73 mu gm(-3), but less change in the summer when the decreases from POA evaporation were similar to the magnitude of added SOA mass. Because the model-performance improvement realized by including the relatively simple pcSOA approach is similar to that of more-complicated parameterizations of OA formation and aging, we recommend caution when applying these more-complicated approaches as they currently rely on numerous uncertain parameters. The pcSOA parameters optimized for performance at the southern and northern California sites lead to higher OA formation than is observed in the CONUS evaluation. This may be due to any of the following: variations in real pcSOA in different regions or time periods, too-high concentrations of other OA sources in the model that are important over the larger domain, or other model issues such as loss processes. This discrepancy is likely regionally and temporally dependent and driven by interferences from factors like varying emissions and chemical regimes.

Lou, S, Russell LM, Yang Y, Liu Y, Singh B, Ghan SJ.  2017.  Impacts of interactive dust and its direct radiative forcing on interannual variations of temperature and precipitation in winter over East Asia. Journal of Geophysical Research: Atmospheres. 122:8761-8780.   10.1002/2017JD027267   AbstractWebsite

We used two 150 year preindustrial simulations of the Community Earth System Model, one with interactive dust and the other with prescribed dust, to quantify the impacts of changes in wind during East Asian winter monsoon (EAWM) season on dust emissions, and the resulting consequences for interannual variations of temperature and precipitation over East Asia. The simulated December-January-February dust column burden and dust optical depth are lower over northern China in the strongest EAWM years than those of the weakest years by 38.3% and 37.2%, respectively. The decrease in dust over the dust source regions and the downwind region leads to an increase in direct radiative forcing (RF) at the surface by up to 1.5 W m−2. The effects of EAWM-related variations in surface winds, precipitation, and their effects on dust emissions and wet removal contribute 67% to the total dust-induced variations of direct RF at the surface and partly offset the cooling that occurs with the EAWM strengthening by heating the surface. The variations of surface air temperature induced by the changes in wind and dust emissions between the strongest and weakest EAWM years (strongest minus weakest) decrease by 0.4–0.6 K from eastern coastal China to Japan, which weakens the impact of EAWM on surface air temperature by 3–18% in these regions. The warming results from the combined effects of changes in direct RF, turbulent heat flux at the surface, and northwesterly wind anomalies that bring cold and dry air from Siberia to these regions. Over eastern coastal China, the variations of large-scale precipitation induced by the feedback of EAWM-related changes in wind on dust emissions decrease by 10–30% in winter because of the reduced changes in surface air temperature and the anomalous circulation.

Liu, J, Russell LM, Lee AKY, McKinney KA, Surratt JD, Ziemann PJ.  2017.  Observational evidence for pollution-influenced selective uptake contributing to biogenic secondary organic aerosols in the southeastern U.S. Geophysical Research Letters. 44:8056-8064.   10.1002/2017GL074665   Abstract

During the 2013 Southern Oxidant and Aerosol Study, aerosol mass spectrometer measurements of submicron mass and single particles were taken at Look Rock, Tennessee. Their concentrations increased during multiday stagnation events characterized by low wind, little rain, and increased daytime isoprene emissions. Organic mass (OM) sources were apportioned as 42% “vehicle-related” and 54% biogenic secondary organic aerosol (bSOA), with the latter including “sulfate-related bSOA” that correlated to sulfate (r = 0.72) and “nitrate-related bSOA” that correlated to nitrate (r = 0.65). Single-particle mass spectra showed three composition types that corresponded to the mass-based factors with spectra cosine similarity of 0.93 and time series correlations of r > 0.4. The vehicle-related OM with m/z 44 was correlated to black carbon, “sulfate-related bSOA” was on particles with high sulfate, and “nitrate-related bSOA” was on all particles. The similarity of the m/z spectra (cosine similarity = 0.97) and the time series correlation (r = 0.80) of the “sulfate-related bSOA” to the sulfate-containing single-particle type provide evidence for particle composition contributing to selective uptake of isoprene oxidation products onto particles that contain sulfate from power plants.

Sanchez, KJ, Roberts GC, Calmer R, Nicoll K, Hashimshoni E, Rosenfeld D, Ovadnevaite J, Preissler J, Ceburnis D, O'Dowd C, Russell LM.  2017.  Top-down and bottom-up aerosol-cloud closure: towards understanding sources of uncertainty in deriving cloud shortwave radiative flux. Atmospheric Chemistry and Physics. 17:9797-9814.   10.5194/acp-17-9797-2017   AbstractWebsite

Top-down and bottom-up aerosol-cloud shortwave radiative flux closures were conducted at the Mace Head Atmospheric Research Station in Galway, Ireland, in August 2015. This study is part of the BACCHUS (Impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding) European collaborative project, with the goal of understanding key processes affecting aerosol-cloud shortwave radiative flux closures to improve future climate predictions and develop sustainable policies for Europe. Instrument platforms include ground-based unmanned aerial vehicles (UAVs)(1) and satellite measurements of aerosols, clouds and meteorological variables. The ground-based and airborne measurements of aerosol size distributions and cloud condensation nuclei (CCN) concentration were used to initiate a 1-D microphysical aerosol-cloud parcel model (ACPM). UAVs were equipped for a specific science mission, with an optical particle counter for aerosol distribution profiles, a cloud sensor to measure cloud extinction or a five-hole probe for 3D wind vectors. UAV cloud measurements are rare and have only become possible in recent years through the miniaturization of instrumentation. These are the first UAV measurements at Mace Head. ACPM simulations are compared to in situ cloud extinction measurements from UAVs to quantify closure in terms of cloud shortwave radiative flux. Two out of seven cases exhibit sub-adiabatic vertical temperature profiles within the cloud, which suggests that entrainment processes affect cloud microphysical properties and lead to an overestimate of simulated cloud shortwave radiative flux. Including an entrainment parameterization and explicitly calculating the entrainment fraction in the ACPM simulations both improved cloud-top radiative closure. Entrainment reduced the difference between simulated and observation-derived cloud-top shortwave radiative flux (delta RF) by between 25 and 60Wm(-2). After accounting for entrainment, satellite-derived cloud droplet number concentrations (CDNCs) were within 30% of simulated CDNC. In cases with a well-mixed boundary layer, delta RF is no greater than 20Wm(-2) after accounting for cloud-top entrainment and up to 50Wm(-2) when entrainment is not taken into account. In cases with a decoupled boundary layer, cloud microphysical properties are inconsistent with ground-based aerosol measurements, as expected, and delta RF is as high as 88Wm(-2), even high (> 30Wm(-2)) after accounting for cloud-top entrainment. This work demonstrates the need to take in situ measurements of aerosol properties for cases where the boundary layer is decoupled as well as consider cloud-top entrainment to accurately model stratocumulus cloud radiative flux.

Saliba, G, Saleh R, Zhao YL, Presto AA, Larnbe AT, Frodin B, Sardar S, Maldonado H, Maddox C, May AA, Drozd GT, Goldstein AH, Russell LM, Hagen F, Robinson AL.  2017.  Comparison of gasoline direct-injection (GDI) and port fuel injection (PFI) vehicle emissions: emission certification standards, cold-start, secondary organic aerosol formation potential, and potential climate impacts. Environmental Science & Technology. 51:6542-6552.   10.1021/acs.est.6b06509   AbstractWebsite

Recent increases in the Corporate Average Fuel Economy standards have led to widespread adoption of vehicles equipped with gasoline direct-injection (GDI) engines. Changes in engine technologies can alter emissions. To quantify these effects, we measured gas- and particle-phase emissions from 82 light-duty gasoline vehicles recruited from the California in-use fleet tested on a chassis dynamometer using the cold-start unified cycle. The fleet included 15 GDI vehicles, including 8 GDIs certified to the most-stringent emissions standard, superultra-low-emission vehicles (SULEV). We quantified the effects of engine technology, emission certification standards, and cold-start on emissions. For vehicles certified to the same emissions standard, there is no statistical difference of regulated gas-phase pollutant emissions between PFIs and GDIs. However, GDIs had, on average, a factor of 2 higher particulate matter (PM) mass emissions than PFIs due to higher elemental carbon (EC) emissions. SULEV certified GDIs have a factor of 2 lower PM mass emissions than GDIs certified as ultralow-emission vehicles (3.0 +/- 1.1 versus 6.3 +/- 1.1 mg/mi), suggesting improvements in engine design and calibration. Comprehensive organic speciation revealed no statistically significant differences in the composition of the volatile organic compounds emissions between PFI and GDIs, including benzene, toluene, ethylbenzene, and xylenes (BTEX). Therefore, the secondary organic aerosol and ozone formation potential of the exhaust does not depend on engine technology. Cold-start contributes a larger fraction of the total unified cycle emissions for vehicles meeting more-stringent emission standards. Organic gas emissions were the most sensitive to cold-start compared to the other pollutants tested here. There were no statistically significant differences in the effects of cold-start on GDIs and PFIs. For our test fleet, the measured 14.5% decrease in CO2 emissions from GDIs was much greater than the potential climate forcing associated with higher black carbon emissions. Thus, switching from PFI to GDI vehicles will likely lead to a reduction in net global warming.

Nicolas, JP, Vogelmann AM, Scott RC, Wilson AB, Cadeddu MP, Bromwich DH, Verlinde J, Lubin D, Russell LM, Jenkinson C, Powers HH, Ryczek M, Stone G, Wille JD.  2017.  January 2016 extensive summer melt in West Antarctica favoured by strong El Niño. 8:15799.   10.1038/ncomms15799   Abstract

Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying areas of the WAIS and is not fully understood. Here we report on an episode of extensive and prolonged surface melting observed in the Ross Sea sector of the WAIS in January 2016. A comprehensive cloud and radiation experiment at the WAIS ice divide, downwind of the melt region, provided detailed insight into the physical processes at play during the event. The unusual extent and duration of the melting are linked to strong and sustained advection of warm marine air toward the area, likely favoured by the concurrent strong El Niño event. The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major melt events.

Yang, Y, Russell LM, Lou SJ, Liao H, Guo JP, Liu Y, Singh B, Ghan SJ.  2017.  Dust-wind interactions can intensify aerosol pollution over eastern China. Nature Communications. 8   10.1038/ncomms15333   AbstractWebsite

Eastern China has experienced severe and persistent winter haze episodes in recent years due to intensification of aerosol pollution. In addition to anthropogenic emissions, the winter aerosol pollution over eastern China is associated with unusual meteorological conditions, including weaker wind speeds. Here we show, based on model simulations, that during years with decreased wind speed, large decreases in dust emissions (29%) moderate the wintertime land-sea surface air temperature difference and further decrease winds by -0.06 (+/- 0.05) ms(-1) averaged over eastern China. The dust-induced lower winds enhance stagnation of air and account for about 13% of increasing aerosol concentrations over eastern China. Although recent increases in anthropogenic emissions are the main factor causing haze over eastern China, we conclude that natural emissions also exert a significant influence on the increases in wintertime aerosol concentrations, with important implications that need to be taken into account by air quality studies.

Kuang, XM, Scott JA, da Rocha GO, Betha R, Price DJ, Russell LM, Cocker DR, Paulson SE.  2017.  Hydroxyl radical formation and soluble trace metal content in particulate matter from renewable diesel and ultra low sulfur diesel in at-sea operations of a research vessel. Aerosol Science and Technology. 51:147-158.   10.1080/02786826.2016.1271938   AbstractWebsite

Reactive oxygen species, including hydroxyl radicals generated by particles, play a role in both aerosol aging and PM2.5 mediated health effects. We assess the impacts of switching marine vessels from conventional diesel to renewable fuel on the ability of particles to generate hydroxyl radical when extracted in a simulated lung lining fluid or in water at pH 3.5, for samples of engine emissions from a research vessel when operating on ultra-low sulfur diesel ( ULSD) and hydrogenation-derived renewable diesel ( HDRD). Samples were collected during dedicated cruises in 2014 and 2015, including aged samples collected by re-intercepting the ship plume. After normalizing to particle mass, particles generated from HDRD combustion had slightly to significantly ( 5-50%) higher OH generation activity than those from ULSD, a difference that was statistically significant for some permutations of year/fuel/engine speed. Water soluble trace metal concentrations and fuel metal concentrations were similar, and compared to urban Los Angeles samples lower in soluble iron and manganese, but similar for most other trace metals. Because PM mass emissions were higher for HDRD, normalizing to fuel increased this difference. Freshly emitted PM had lower activity than the "plume chase" samples, and samples collected on the ship had lower activity than the urban reference. The differences in OH production correlated reasonably well with redox-active transition metals, most strongly with soluble manganese, with roles for vanadium and likely copper and iron. The results also suggest that atmospheric processing of fresh combustion particles rapidly increases metal solubility, which in turn increases OH production.