Publications

Export 2 results:
Sort by: Author Title Type [ Year  (Desc)]
2007
Yum, SS, Roberts G, Kim JH, Song KY, Kim DY.  2007.  Submicron aerosol size distributions and cloud condensation nuclei concentrations measured at Gosan, Korea, during the Atmospheric brown clouds - East Asian Regional Experiment 2005. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd008212   AbstractWebsite

Submicron aerosol size distributions, CN and CCN concentrations at a constant supersaturation of 0.6% were measured at a relatively remote coastal site at Gosan in Jeju Island, Korea, during the ABC-EAREX from 11 March to 8 April 2005. The average CN concentrations were 6088 +/- 3988, 5231 +/- 2454 and 3513 +/- 1790 cm(-3), respectively, for the three major air mass types classified by their origins. The corresponding CCN concentrations were 2393 +/- 1156, 2897 +/- 1226 and 1843 +/- 585 cm(-3). The type III air mass was the closest to maritime origins, but these lowest concentrations at Gosan were an order of magnitude higher than those of clean marine boundary layer, indicating that regardless of air mass designation springtime submicron aerosols at Gosan were under steady continental influences. Distinct new particle formation and growth events occurred on 6 d, when clear sky weather conditions prevailed that brought air from northern China, Mongolia or Russia by anticyclonic circulations. Simultaneous occurrence of these events at a western coastal site in the Korean Peninsula 350 km north of Gosan suggests that these events were not local but at least regional-scale events. CCN concentrations were predicted with the aerosol size distributions and the assumption of particles being composed of ( NH(4))(2)SO(4). The predicted to measured CCN concentration ratio was 1.27 +/- 0.29 and the r(2) was 0.77 for the whole measurement period. The type I air mass that has the most continental influences showed a slight tendency to overpredict CCN concentrations but the good agreement overall suggests that springtime Gosan aerosols act almost like ammonium sulfate as far as CCN activity is concerned, almost regardless of air mass origin.

2006
Roberts, G, Mauger G, Hadley O, Ramanathan V.  2006.  North American and Asian aerosols over the eastern Pacific Ocean and their role in regulating cloud condensation nuclei. Journal of Geophysical Research-Atmospheres. 111   10.1029/2005jd006661   AbstractWebsite

[ 1] Measurements of aerosol and cloud properties in the Eastern Pacific Ocean were taken during an airborne experiment on the University of Wyoming's King Air during April 2004 as part of the Cloud Indirect Forcing Experiment (CIFEX). We observed a wide variety of aerosols, including those of long-range transport from Asia, clean marine boundary layer, and North American emissions. These aerosols, classified by their size distribution and history, were found in stratified layers between 500 to 7500 m above sea level and thicknesses from 100 to 3000 m. A comparison of the aerosol size distributions to measurements of cloud condensation nuclei (CCN) provides insight to the CCN activity of the different aerosol types. The overall ratio of measured to predicted CCN concentration (NCCN) is 0.56 +/- 0.41 with a relationship of N-CCN,N- measured = N-CCN, predicted(0.846 +/- 0.002) for 23 research flights and 1884 comparisons. Such a relationship does not accurately describe a CCN closure; however, it is consistent with our measurements that high CCN concentrations are more influenced by anthropogenic sources, which are less CCN active. While other CCN closures have obtained results closer to the expected 1: 1 relationship, the different aerosol types ( and presumably differences in aerosol chemistry) are responsible for the discrepancy. The measured N-CCN at 0.3% supersaturation (S-c) ranged from 20 cm(-3) (pristine) to 350 cm(-3) ( anthropogenic) with an average of 106 +/- 54 cm(-3) over the experiment. The inferred supersaturation in the clouds sampled during this experiment is similar to 0.3%. CCN concentrations of cloud-processed aerosol were well predicted using an ammonium sulfate approximation for S-c <= 0.4%. Predicted N-CCN for other aerosol types (i.e., Asian and North American aerosols) were high compared to measured values indicating a less CCN active aerosol. This study highlights the importance of chemical effects on CCN measurements and introduces a CCN activation index as a method of classifying the efficiency of an aerosol to serve as CCN relative to an ammonium sulfate particle. This index ranged from close to unity for cloud processed aerosols to as low as 0.31 for aged aerosols transported from Asia. We also compare the performance of two CCN instruments ( static thermal diffusion chamber and streamwise continuous flow chamber) on a 45 minute level leg where we observe an aged layer and a nucleation event. More than 50% of the aged aerosol served as CCN at 0.2% S-c, primarily owing to their large size, while CCN concentrations during the nucleation event were close to 0 cm(-3). CCN concentrations from both instruments agreed within instrument errors; however, the continuous flow chamber effectively captured the rapid transition in aerosol properties.