Publications

Export 17 results:
Sort by: Author Title [ Year  (Desc)]
2017
Arndt, J, Sciare J, Mallet M, Roberts GC, Marchand N, Sartelet K, Sellegri K, Dulac F, Healy RM, Wenger JC.  2017.  Sources and mixing state of summertime background aerosol in the north-western Mediterranean basin. Atmospheric Chemistry and Physics. 17:6975-7001.   10.5194/acp-17-6975-2017   AbstractWebsite

An aerosol time-of-flight mass spectrometer (ATOFMS) was employed to provide real-time single particle mixing state and thereby source information for aerosols impacting the western Mediterranean basin during the ChArMEx-ADRIMED and SAF-MED campaigns in summer 2013. The ATOFMS measurements were made at a ground-based remote site on the northern tip of Corsica. Twenty-seven distinct ATOFMS particle classes were identified and subsequently grouped into eight general categories: EC-rich (elemental carbon), K-rich, Na-rich, amines, OC-rich (organic carbon), V-rich, Fe-rich and Ca-rich particles. Mass concentrations were reconstructed for the ATOFMS particle classes and found to be in good agreement with other co-located quantitative measurements (PM1, black carbon (BC), organic carbon, sulfate mass and ammonium mass). Total ATOFMS reconstructed mass (PM2.5) accounted for 70-90% of measured PM10 mass and was comprised of regionally transported fossil fuel (EC-rich) and biomass burning (K-rich) particles. The accumulation of these transported particles was favoured by repeated and extended periods of air mass stagnation over the western Mediterranean during the sampling campaigns. The single particle mass spectra proved to be valuable source markers, allowing the identification of fossil fuel and biomass burning combustion sources, and was therefore highly complementary to quantitative measurements made by Particle into Liquid Sampler ion chromatography (PILS-IC) and an aerosol chemical speciation monitor (ACSM), which have demonstrated that PM1 and PM10 were comprised predominantly of sulfate, ammonium and OC. Good temporal agreement was observed between ATOFMS EC-rich and K-rich particle mass concentrations and combined mass concentrations of BC, sulfate, ammonium and low volatility oxygenated organic aerosol (LV-OOA). This combined information suggests that combustion of fossil fuels and biomass produced primary EC- and OC-containing particles, which then accumulated ammonium, sulfate and alkylamines during regional transport. Three other sources were also identified: local biomass burning, marine and shipping. Local combustion particles

2012
Qin, XY, Pratt KA, Shields LG, Toner SM, Prather KA.  2012.  Seasonal comparisons of single-particle chemical mixing state in Riverside, CA. Atmospheric Environment. 59:587-596. Abstract

The Study of Organic Aerosols in Riverside, CA (SOAR) field campaign, conducted in the summer and fall of 2005, focused on developing a stronger understanding of seasonal influences on the sources and processes contributing to some of the highest levels of particulate matter in the United States. On-line single-particle mass spectrometry measurements showed that carbonaceous particles generally dominated the submicron size range (>75% by number), compared to primarily aged sea salt and dust in the supermicron size range. During periods with high PM2.5 (particulate matter <2.5 mu m) mass and number concentrations, hygroscopic water-containing carbonaceous particles internally mixed with sulfate and nitrate extended up into the supermicron size mode. The mixing state of carbonaceous particles changed with season. In the summer, carbonaceous particles were primarily mixed with secondary (oxidized) organic carbon and sulfate; whereas in the fall, they were mixed mostly with ammonium nitrate. During each season, different processes contributed to the highest pollution levels. In the summer, photochemical production of highly aged secondary organic carbon resulted in daily peaks in both number and mass particle concentrations, followed by removal in the afternoon by the arrival of the clean marine air masses from the coast. In contrast, cooler, more stagnant meteorological conditions in the fall season resulted in the buildup over several days of submicron carbonaceous particles mixed with semivolatile ammonium, nitrate, and amines. In addition, Santa Ana wind events in the fall led to dust and biomass burning particles dominating both the submicron and supermicron size ranges. Published by Elsevier Ltd.

2011
Hatch, LE, Creamean JM, Ault AP, Surratt JD, Chan MN, Seinfeld JH, Edgerton ES, Su YX, Prather KA.  2011.  Measurements of Isoprene-Derived Organosulfates in Ambient Aerosols by Aerosol Time-of-Flight Mass Spectrometry - Part 1: Single Particle Atmospheric Observations in Atlanta. Environmental Science & Technology. 45:5105-5111.   10.1021/es103944a   AbstractWebsite

Organosulfate species have recently been identified as a potentially significant class of secondary organic aerosol (SOA) species, yet little is known about their behavior in the atmosphere. In this work, organosulfates were observed in individual ambient aerosols using single particle mass spectrometry in Atlanta, GA during the 2002 Aerosol Nucleation and Characterization Experiment (ANARChE) and the 2008 August Mini-Intensive Gas and Aerosol Study (AMIGAS). Organosulfates derived from biogenically produced isoprene were detected as deprotonated molecular ions in negative-ion spectra measured by aerosol time-of-flight mass spectrometry; comparison to high-resolution mass spectrometry data obtained from filter samples corroborated the peak assignments. The size-resolved, chemical composition measurements revealed that organosulfate species were mostly detected in submicrometer aerosols and across a range of aerosols from different sources, consistent with secondary reaction products. Detection of organosulfates in a large fraction of negative-ion ambient spectra -ca. 90-95% during ANARChE and similar to 65% of submicrometer particles in AMIGAS highlights the ubiquity of organosulfate species in the ambient aerosols of biogenically influenced urban environments.

2009
Pratt, KA, Mayer JE, Holecek JC, Moffet RC, Sanchez RO, Rebotier TP, Furutani H, Gonin M, Fuhrer K, Su YX, Guazzotti S, Prather KA.  2009.  Development and Characterization of an Aircraft Aerosol Time-of-Flight Mass Spectrometer. Analytical Chemistry. 81:1792-1800.   10.1021/ac801942r   AbstractWebsite

Vertical and horizontal profiles of atmospheric aerosols are necessary for understanding the impact of air pollution on regional and global climate. To gain further insight into the size-resolved chemistry of individual atmospheric particles, a smaller aerosol time-of-flight mass spectrometer (ATOFMS) with increased data acquisition capabilities was developed for aircraft-based studies. Compared to previous ATOFMS systems, the new instrument has a faster data acquisition rate with improved ion transmission and mass resolution, as well as reduced physical size and power consumption, all required advances for use in aircraft studies. In addition, real-time source apportionment software allows the immediate identification and classification of individual particles to guide sampling decisions while in the field. The aircraft (A)-ATOFMS was field-tested on the ground during the Study of Organic Aerosols in Riverside, CA (SOAR) and aboard an aircraft during the Ice in Clouds Experiment-Layer Clouds (ICEL). Initial results from ICE-L represent the first reported aircraft-based single-particle dual-polarity mass spectrometry measurements and provide an increased understanding of particle mixing state as a function of altitude. Improved ion transmission allows for the first single-particle detection of species out to similar to m/z 2000, an important mass range for the detection of biological aerosols and oligomeric species. In addition, high time resolution measurements of single-particle mixing state are demonstrated and shown to be important for airborne studies where particle concentrations and chemistry vary rapidly.

2008
Prather, KA, Hatch CD, Grassian VH.  2008.  Analysis of Atmospheric Aerosols. Annual Review of Analytical Chemistry. 1:485-514., Palo Alto: Annual Reviews   10.1146/annurev.anchem.1.031207.113030   Abstract

Aerosols represent an important component of the Earth's atmosphere. Because aerosols are composed of solid and liquid particles of varying chemical complexity size, and phase, large challenges exist in understanding how they impact climate, health, and the chemistry of the atmosphere. Only through the integration of field, laboratory,, and modeling analysis can we begin to unravel the roles atmospheric aerosols play in these global processes. In this article, we provide a brief review of the current state of the science in the analysis of atmospheric aerosols and some important challenges that need to be overcome before they can become fully integrated. It is clear that only when these areas are effectively bridged can we fully understand the impact that atmospheric aerosols have on our environment and the Earth's system at the level of scientific certainty necessary to design and implement sound environmental policies.

2004
Wenzel, RJ, Prather KA.  2004.  Improvements in ion signal reproducibility obtained using a homogeneous laser beam for on-line laser desorption/ionization of single particles. Rapid Communications in Mass Spectrometry. 18:1525-1533.   10.1002/rcm.1509   AbstractWebsite

A major factor limiting on-line single particle mass spectrometry techniques from becoming more quantitative is the large shot-to-shot variability in ion intensities observed in the laser desorption/ionization (LDI) mass spectra. 1,2 In previous work, lab-generated particles showed fluctuations of up to 152% in the absolute ion intensities in averaged spectra of 200-300 'identical' particles.(2) Most of these fluctuations were attributed to inhomogeneities in the laser beam profile, leading to significant differences in the power each particle encountered depending on the position in the LDI laser beam where it underwent analysis. The goal of the work presented herein is to determine whether a fiber optic actually reduces the observed variability in single particle LDI mass spectral data. Initial results are presented for individual single component organic particles composed of 2,4-dihydroxybenzoic acid (2,4-DHB) analyzed using a low-power flat-top laser beam profile created by sending an ultraviolet (266 nm) DI laser through a fiber optic. Relative standard deviations of the total ion intensities for peaks in individual spectra are reduced to 31%. Single particle spectra, compared with and without laser homogenization at the same nominal laser fluence, show a marked enhancement. Specifically, the ion signal patterns of the 2,4-DHB particle spectra obtained using a homogenous LDI beam look identical to one another (i.e. only one particle type was produced with a commonly used neural network grouping algorithm), whereas without beam homogenization 25 different particle types (based on ion intensity patterns) were obtained. Future publications will explore more particle types and matrices but the initial results described herein are quite encouraging. Copyright (C) 2004 John Wiley Sons, Ltd.

2003
Whiteaker, JR, Prather KA.  2003.  Hydroxymethanesulfonate as a tracer for fog processing of individual aerosol particles. Atmospheric Environment. 37:1033-1043.   10.1016/s1352-2310(02)01029-4   AbstractWebsite

Hydroxymethanesulfonate (HMS), an important component in fog and cloud systems, is identified in the negative ion mass spectra of individual particles sampled with an aerosol time-of-flight mass spectrometer (ATOFMS). The peak assignment at mass/charge (m/z)- 1 1 1 is confirmed by analyzing HMS particles produced in the laboratory. Individual particle mass spectra from a field campaign in Bakersfield, California reveal the presence of HMS in the ambient aerosol during isolated time periods near the dissipation phase of fog suggesting fog processing of the aerosol. The lifetime of HMS in the aerosol is limited to less than 12 h. Using the presence of HMS as a tracer for aqueous-phase fog processing, the size distribution indicates that particles with aerodynamic diameters greater than 0.7 mum are most affected by the fog and associated high relative humidity. HMS is predominantly associated with particles containing carbon, ammonium, sulfate, and nitrate. Examination of elemental carbon particles containing HMS shows the presence of organic carbon which most likely enhances the hygroscopicity of these particles. This study demonstrates the ability for real-time measurements of fog processing at the single particle level using a chemical tracer for aqueous-phase reactions and highlights the possibilities for using high temporal resolution measurements to gain unique insights into atmospheric processes. (C) 2003 Elsevier Science Ltd. All rights reserved.

Whiteaker, JR, Prather KA.  2003.  Detection of pesticide residues on individual particles. Analytical Chemistry. 75:49-56.   10.1021/ac025771v   AbstractWebsite

An aerosol time-of-flight mass spectrometer (ATOFMS) is used to analyze the size and composition of individual particles containing pesticides. Pesticide residues are found in the atmosphere as a result of spray drift, volatilization, and suspension of coated soils. The ability of the ATOFMS to identify the presence of these contaminants, on individual particles is assessed for particles created from pure solutions of several commonly used pesticides, as well as pesticides mixed with an organic matrix, and coated on soils. The common names of the pesticides studied are 2,4-D, atrazine, chlorpyrifos, malathion, permethrin, and propoxur. Analysis of the mass spectra produced by single- and two-step laser desorption/ionization of pesticide-containing particles allows for identification of peaks that can be used for detection of pesticide residues in the ambient aerosol. The identified marker peaks are used to approximate detection limits for the pesticides applied to soils, which are on the order of a fraction of a monolayer for individual particles. Results suggest that this technique may be useful for studying the real-time partitioning and distribution of pesticides in the atmosphere immediately following application in agricultural regions.

2002
Bhave, PV, Allen JO, Morrical BD, Fergenson DP, Cass GR, Prather KA.  2002.  A field-based approach for determining ATOFMS instrument sensitivities to ammonium and nitrate. Environmental Science & Technology. 36:4868-4879.   10.1021/es015823i   AbstractWebsite

Aerosol time-of-flight mass spectrometry (ATOFMS) instruments measure the size and chemical composition of individual particles in real-time. ATOFMS chemical composition measurements are difficult to quantify, largely because the instrument sensitivities to different chemical species in mixed ambient aerosols are unknown. In this paper, we develop a field-based approach for determining ATOFMS instrument sensitivities to ammonium and nitrate in size-segregated atmospheric aerosols, using tandem ATOFMS-impactor sampling. ATOFMS measurements are compared with collocated impactor measurements taken at Riverside, CA, in September 1996, August 1997, and October 1997. This is the first comparison of ion signal intensities from a single-particle instrument with quantitative measurements of atmospheric aerosol chemical composition. The comparison reveals that ATOFMS instrument sensitivities to both NH4+ and NO3- decline with increasing particle aerodynamic diameter over a 0.32-1.8 mum calibration range. The stability of this particle size dependence is tested over the broad range of fine particle concentrations (PM1.8 = 17.6 +/- 2.0-127.8 +/- 1.8 mug m(-3)), ambient temperatures (23-35 degreesC), and relative humidity conditions (21-69%), encountered during the field experiments. This paper describes a potentially generalizable methodology for increasing the temporal and size resolution of atmospheric aerosol chemical composition measurements, using tandem ATOFMS-impactor sampling.

2001
Guazzotti, SA, Coffee KR, Prather KA.  2001.  Continuous measurements of size-resolved particle chemistry during INDOEX-Intensive Field Phase 99. Journal of Geophysical Research-Atmospheres. 106:28607-28627.   10.1029/2001jd900099   AbstractWebsite

During the Indian Ocean Experiment intensive Field Phase 99, aerosol time-of-flight mass spectrometry (ATOFMS) was used for on-line characterization of the size and chemical composition of individual particles. High temporal resolution single-particle measurements were made on the Island of Kaashidhoo and on board the Research Vessel Ronald H. Brown during February and March, respectively. Sea-salt and dust particles are the ma or contributors to the aerosol between 1.0 and 2.5 mum. For particles with aerodynamic diameters between 0.2 and 1.0 mum, carbon-containing particles dominated. Differences in the chemical composition of the sampled aerosol were observed for different days and locations, and can be correlated with back trajectory information. For locations north of the Intertropical Convergence Zone (ITCZ), anthropogenic influences on the aerosol chemical composition were indicated by increased contributions from sea-salt particles with non-seasalt (nss) sulfates, dust with sulfates, and, carbon-containing particles with potassium and sulfates. In contrast, in regions close to and south of the ITCZ, the aerosol showed characteristics consistent with a more pristine marine environment. The relative contributions from sulfate-associated particles were evaluated from the single-particle data, as well. The observed sulfate aerosols over the size range analyzed in this study (i.e., aerodynamic diameter between 0.2 and 2.5 mum) consist exclusively of sulfates associated with sea salt, dust, elemental carbon, and/or organic matter. Quantitative contributions from the, different types of sulfate-associated particles are evaluated at different locations during the IFP: southern latitude, midlatitude, northern latitude at the Arabian Sea, and mid/northern latitude at the Bay of Bengal.

2000
Silva, PJ, Prather KA.  2000.  Interpretation of mass spectra from organic compounds in aerosol time-of-flight mass spectrometry. Analytical Chemistry. 72:3553-3562.   10.1021/ac9910132   AbstractWebsite

Organic compounds containing a variety of functional groups have been analyzed using aerosol time-of-flight mass spectrometry, Both positive and negative laser desorption/ionization mass spectra have been acquired for compounds of relevance to ambient air particulate matter, including polycyclic aromatic hydrocarbons, heterocyclic analogues, aromatic oxygenated compounds such as phenols and acids, aliphatic dicarboxylic acids, and reduced nitrogen species such as amines. In many cases, positive ion mass spectra are similar to those found in libraries for 70-eV electron impact mass spectrometry. However, formation of even-electron molecular ions due to adduct formation also plays a major role in ion formation, Negative ion mass spectra suggest that organic compounds largely disintegrate into carbon cluster fragments (C-n(-) and CnH-). However, information about the heteroatoms present in organic molecules, especially nitrogen and oxygen, is carried dominantly by negative ion spectra, emphasizing the importance of simultaneous analysis of positive and negative ions in atmospheric samples.

Silva, PJ, Carlin RA, Prather KA.  2000.  Single particle analysis of suspended soil dust from Southern California. Atmospheric Environment. 34:1811-1820.   10.1016/s1352-2310(99)00338-6   AbstractWebsite

Single particle analysis of soil dust has been performed using aerosol time-of-flight mass spectrometry. The presence of crustal elements is observed in the mass spectra of individual particles. Aluminum and iron constitute the two most commonly detected cations. Other common cations observed in the mass spectra of soil particles include sodium, magnesium, potassium, calcium, titanium, and barium, and also lithium and lanthanide oxides which are not detectable by conventional techniques such as X-ray fluorescence. Silicates make up the bulk of detected anions, although the presence of phosphate is also observed. Characteristic peaks in both the positive and negative ion mass spectra enable us to identify individual dust particles in atmospheric samples and track chemically distinct dust particles in the atmosphere with a temporal resolution of 15 min using aerosol time-of-flight mass spectrometry. (C) 2000 Elsevier Science Ltd. All rights reserved.

1999
Silva, PJ, Liu DY, Noble CA, Prather KA.  1999.  Size and chemical characterization of individual particles resulting from biomass burning of local Southern California species. Environmental Science & Technology. 33:3068-3076.   10.1021/es980544p   AbstractWebsite

The chemical composition and size of individual particles derived from combustion products of several species found in Southern California were obtained using aerosol time-of-flight mass spectrometry. The major inorganic species observed in >90% of all biomass burning particles is potassium, indicated by the atomic ion, as well as clusters containing chloride, nitrate, and sulfate ions in the mass spectra. By obtaining positive and negative ion mass spectra it is possible to identify distinct chemical marker combinations in particles resulting From the burning of plant species, which in turn allows for differentiation from particles produced from other combustion sources such as vehicle emissions. Using these markers, particles derived from biomass burning were identified. in ambient aerosol samples.

1997
Silva, PJ, Prather KA.  1997.  On-line characterization of individual particles from automobile emissions. Environmental Science & Technology. 31:3074-3080.   10.1021/es961063d   AbstractWebsite

This paper presents results from a study showing the first on-line measurement of the size and chemical composition of individual particles emitted in automobile exhaust. Particles sampled directly from the exhaust pipes of a number of vehicles upon startup were analyzed using aerosol time-of-flight mass spectrometry (ATOFMS). Both organic and inorganic chemical species including lead, cerium, platinum, molybdenum, calcium, and sodium were observed in individual exhaust particles. In general, a qualitative correlation exists between particle size and composition, typified by the presence of predominately organic species in particles in the fine size mode (<1 mu m) and inorganic species in particles in the coarse size mode (>1 mu m). This study demonstrates the potential of using ATOFMS for analyzing vehicular exhaust in an on-line matter. Ultimately, ATOFMS can be used as a real-time monitor, characterizing particles produced from vehicles under a variety of well-defined operating conditions that will allow for further development of the understanding of particle formation and reaction processes. Furthermore, determination of chemical tracers in individual exhaust particles will allow for more accurate source allocation of atmospheric particles.

1995
Georgakakos, KP, Bae DH, Cayan DR.  1995.  HYDROCLIMATOLOGY OF CONTINENTAL WATERSHEDS .1. TEMPORAL ANALYSES. Water Resources Research. 31:655-675.   10.1029/94wr02375   AbstractWebsite

The linkage between meteorology/climate and hydrology of temperate latitude catchments on daily to decade time scales is studied. Detailed hydrology is provided by a hydrologic catchment model, adapted from the operational streamflow forecast model of the National Weather Service River Forecast System. The model is tuned to respond to observed daily precipitation and potential evaporation input. Results from the Bird Creek basin with outlet near Sperry, Oklahoma, and from the Boone River basin with outlet at Webster City, Iowa, indicate that the model quite accurately simulates the observed daily discharge over 40 years at each of the two 2000-km(2) basins. Daily cross-correlations between observed and simulated basin outflows were better than 0.8 for both basins over a 40-year historical period. Soil moisture variability over a period of four decades is studied, and an assessment of temporal and spatial (as related to the separation distance of the two basins) scales present in the estimated soil moisture record is made. Negative soil. water anomalies have larger magnitudes than positive anomalies, and comparison of the simulated soil water records of the two basins indicates spatial scales of variability that in several cases are as long as the interbasin distance. The temporal scales of soil water content are considerably longer than those of the forcing atmospheric variables for all seasons and both basins. Timescales of upper and total soil water content anomalies are typically 1 and 3 months, respectively. Linkage between the hydrologic components and both local and regional-to-hemispheric atmospheric variability is studied, both for atmosphere forcing hydrology and hydrology forcing atmosphere. For both basins, crosscorrelation analysis shows that local precipitation strongly forces soil water in the upper soil layers with a 10-day lag. There is no evidence of soil water feedback to local precipitation. However, significant cross-correlation values are obtained for upper soil water leading daily maximum temperature with 5-10 day lags, especially during periods of extremely high or low soil water content. Complementary results of a spatial hydroclimatic analysis are presented in a companion paper (Cayan and Georgakakos, this issue).

Georgakakos, KP, Bae DH, Cayan DR.  1995.  Hydroclimatology of continental watersheds: 1. Temporal Analyses. Water Resources Research. 31:655-675.   10.1029/94wr02375   AbstractWebsite

The linkage between meteorology/climate and hydrology of temperate latitude catchments on daily to decade time scales is studied. Detailed hydrology is provided by a hydrologic catchment model, adapted from the operational streamflow forecast model of the National Weather Service River Forecast System. The model is tuned to respond to observed daily precipitation and potential evaporation input. Results from the Bird Creek basin with outlet near Sperry, Oklahoma, and from the Boone River basin with outlet at Webster City, Iowa, indicate that the model quite accurately simulates the observed daily discharge over 40 years at each of the two 2000-km(2) basins. Daily cross-correlations between observed and simulated basin outflows were better than 0.8 for both basins over a 40-year historical period. Soil moisture variability over a period of four decades is studied, and an assessment of temporal and spatial (as related to the separation distance of the two basins) scales present in the estimated soil moisture record is made. Negative soil. water anomalies have larger magnitudes than positive anomalies, and comparison of the simulated soil water records of the two basins indicates spatial scales of variability that in several cases are as long as the interbasin distance. The temporal scales of soil water content are considerably longer than those of the forcing atmospheric variables for all seasons and both basins. Timescales of upper and total soil water content anomalies are typically 1 and 3 months, respectively. Linkage between the hydrologic components and both local and regional-to-hemispheric atmospheric variability is studied, both for atmosphere forcing hydrology and hydrology forcing atmosphere. For both basins, crosscorrelation analysis shows that local precipitation strongly forces soil water in the upper soil layers with a 10-day lag. There is no evidence of soil water feedback to local precipitation. However, significant cross-correlation values are obtained for upper soil water leading daily maximum temperature with 5-10 day lags, especially during periods of extremely high or low soil water content. Complementary results of a spatial hydroclimatic analysis are presented in a companion paper (Cayan and Georgakakos, this issue).

Georgakakos, KP, Bae DH, Cayan DR.  1995.  Hydroclimatology of continental watersheds: 1. Temporal Analyses. Water Resources Research. 31:655-675.   10.1029/94wr02375   AbstractWebsite

The linkage between meteorology/climate and hydrology of temperate latitude catchments on daily to decade time scales is studied. Detailed hydrology is provided by a hydrologic catchment model, adapted from the operational streamflow forecast model of the National Weather Service River Forecast System. The model is tuned to respond to observed daily precipitation and potential evaporation input. Results from the Bird Creek basin with outlet near Sperry, Oklahoma, and from the Boone River basin with outlet at Webster City, Iowa, indicate that the model quite accurately simulates the observed daily discharge over 40 years at each of the two 2000-km(2) basins. Daily cross-correlations between observed and simulated basin outflows were better than 0.8 for both basins over a 40-year historical period. Soil moisture variability over a period of four decades is studied, and an assessment of temporal and spatial (as related to the separation distance of the two basins) scales present in the estimated soil moisture record is made. Negative soil. water anomalies have larger magnitudes than positive anomalies, and comparison of the simulated soil water records of the two basins indicates spatial scales of variability that in several cases are as long as the interbasin distance. The temporal scales of soil water content are considerably longer than those of the forcing atmospheric variables for all seasons and both basins. Timescales of upper and total soil water content anomalies are typically 1 and 3 months, respectively. Linkage between the hydrologic components and both local and regional-to-hemispheric atmospheric variability is studied, both for atmosphere forcing hydrology and hydrology forcing atmosphere. For both basins, crosscorrelation analysis shows that local precipitation strongly forces soil water in the upper soil layers with a 10-day lag. There is no evidence of soil water feedback to local precipitation. However, significant cross-correlation values are obtained for upper soil water leading daily maximum temperature with 5-10 day lags, especially during periods of extremely high or low soil water content. Complementary results of a spatial hydroclimatic analysis are presented in a companion paper (Cayan and Georgakakos, this issue).