Laboratory Studies of the Cloud Droplet Activation Properties and Corresponding Chemistry of Saline Playa Dust

Abstract

Playas emit large quantities of dust that can facilitate the activation of cloud droplets. Despite the potential importance of playa dusts for cloud formation, most climate models assume that all dust is nonhygroscopic; however, measurements are needed to clarify the role of dusts in aerosol-cloud interactions. Here, we report measurements of CCN activation from playa dusts and parameterize these results in terms of both κ-Koḧler theory and adsorption activation theory for inclusion in atmospheric models. κ ranged from 0.002 ± 0.001 to 0.818 ± 0.094, whereas Frankel-Halsey-Hill (FHH) adsorption parameters of A FHH = 2.20 ± 0.60 and B FHH = 1.24 ± 0.14 described the water uptake properties of the dusts. Measurements made using aerosol time-offlight mass spectrometry (ATOFMS) revealed the presence of halite, sodium sulfates, and sodium carbonates that were strongly correlated with κ underscoring the role that mineralogy, including salts, plays in water uptake by dust. Predictions of κ made using bulk chemical techniques generally showed good agreement with measured values. However, several samples were poorly predicted suggesting that chemical heterogeneities as a function of size or chemically distinct particle surfaces can determine the hygroscopicity of playa dusts. Our results further demonstrate the importance of dust in aerosol−cloud interactions.

Hygroscopic Properties of Saline Mineral Dust From Different Regions in China: Geographical Variations, Compositional Dependence, and Atmospheric Implications

“…Overall, Figures and suggested in a qualitative manner that chemical composition played a key role in hygroscopic properties of saline mineral dust. Similar conclusions were drawn by Gaston et al () for saline mineral dust in North America, who found good correlations between CCN activities and aerosol composition measured using aerosol time‐of‐flight mass spectrometry.…”

“…For example, the measured κ was 0.052 ± 0.004 for one sample (TX Salt Basin Site S3), significantly larger than the predicted value (0.001); on the other hand, κ were measured to be 0.041 ± 0.006 and 0.033 ± 0.004 for another two samples (Great Salt Lake “Puffy Soil” and Great Salt Lake “Salt Crust”), approximately 1 order of magnitude smaller than corresponding predicted values (0.374 and 0.348, respectively). Overall, the agreement between measurement and calculation appeared to be better in our present work, when compared to the study by Gaston et al (). Both studies used the bulk average chemical composition, measured using IC, as input for thermodynamic calculations; however, our work measured hygroscopic growth of bulk samples, whereas Gaston et al () measured the CCN activities of aerosol particles, the chemical composition of which may be different from those for the bulk samples.…”

“…This observation was further supported by laboratory studies which showed that saline mineral dust particles in North America exhibited considerably high hygroscopicity and CCN activity (Gaston et al, ; Koehler et al, ). For example, κ values were measured to be in the range of <0.01 to >0.8 for saline mineral dust particles collected in North America (Gaston et al, ), displaying large geographical variations. In our work we measured hygroscopic growth of saline mineral dust particles in China, and also found that the derived κ values varied from <0.01 to >1.…”

“…Gaston et al () used ISORROPIA‐II to predict κ values for saline mineral dust samples collected in North America, and compared predicted values with those derived from CCN activity measurements. Fairly good agreement between prediction and measurement was found for most of the sample, although large discrepancies also existed for a few samples (Gaston et al, ).…”

“…The calculated mass factors at 90% RH were 31% and 24% smaller than the measured values for XJ-5 and NX, respectively; in contrast, for XJ-6, the calculated mass growth factor at 90% RH was 97% larger than the measured value. Gaston et al (2017) used ISORROPIA-II to predict κ values for saline mineral dust samples collected in North America, and compared predicted values with those derived from CCN activity measurements. Fairly good agreement between prediction and measurement was found for most of the sample, although large discrepancies also existed for a few samples (Gaston et al, 2017).…”