Offline analysis of the chemical composition and hygroscopicity of submicrometer aerosol at an Asian outflow receptor site and comparison with online measurements

Abstract

Abstract. Filter-based offline analysis of atmospheric aerosol hygroscopicity coupled to composition analysis provides information complementary to that obtained from online analysis. However, its application itself and comparison to online analysis have remained limited to date. In this study, daily submicrometer aerosol particles (PM0.95, 50 % cutoff diameter 0.95 µm) were collected onto quartz fiber filters on Okinawa Island, a receptor of East Asian outflow, in the autumn of 2015. The chemical composition of water-soluble matter (WSM) in PM0.95, PM0.95 itself, and their respective hygroscopicities were characterized through the offline use of an aerosol mass spectrometer and a hygroscopicity tandem differential mobility analyzer. Thereafter, results were compared with those obtained from online analyses. Sulfate dominated the WSM mass (59 %), followed by water-soluble organic matter (WSOM, 20 %) and ammonium (13 %). WSOM accounted for most (91 %) of the mass of extracted organic matter (EOM) and the atomic O-to-C ratios (O:C) of WSOM and EOM were high (mean ± standard deviation were 0.84 ± 0.08 and 0.78 ± 0.08, respectively), both of which indicate highly aged characteristics of the observed aerosol. The hygroscopic growth curves showed clear hysteresis for most samples. At 85 % relative humidity (RH), the calculated hygroscopicity parameter κ values of the WSM (κWSM), WSOM, EOM, and PM0.95 (κPM0.95) were 0.50 ± 0.03, 0.22 ± 0.12, 0.20 ± 0.11, and 0.47 ± 0.03, respectively. An analysis using the thermodynamic Extended Aerosol Inorganics Model (E-AIM) shows, on average, that inorganic salts and WSOM contributed 88 % and 12 %, respectively, of the κWSM (or κPM0.95). High similarities were found between offline and online analysis for chemical compositions that are related to particle hygroscopicity (the mass fractions and O:C of organics and the degree of neutralization) and also for aerosol hygroscopicity. As possible factors governing the variation in κWSM, the influences of WSOM abundance and the neutralization of inorganic salts were assessed. At high RH (70 %–90 %), the hygroscopicity of WSM and PM0.95 was affected considerably by the presence of organic components; at low RH (20 %–50 %), the degree of neutralization could be important. This study not only characterized aerosol hygroscopicity at the receptor site of East Asian outflow but also shows that offline hygroscopicity analysis is an appropriate method, at least for aerosols of the studied type. The results encourage further applications to other environments and to more in-depth hygroscopicity analysis, in particular for organic fractions.

The influence of aerosol hygroscopicity on clouds and precipitation over Western Ghats, India

“…It is revealed that κ modulates CDSD (i.e., growth of cloud droplets) from the initial mixing state to the well‐mixed state in conjunction with two modes of aerosols. The numerical simulations propose that hygroscopicity of aerosol particles in the accumulation mode might be more important (Figure 4b,d), which is similar to results from a recent study by Deng et al (2022). The hygroscopicity indicates the activation of smaller droplets, which may help for invigorating the cloud by uplifting below the freezing level due to a strong updraft, influencing the rain intensity.…”

The Influence of Aerosol Hygroscopicity on Clouds and Precipitation over Western Ghats, India

“…manuscript submitted to Journal of Geophysical Research-Atmosphere clearly propose that the hygroscopicity of aerosol particles in the accumulation mode might be more important (Fig.4b,d), which is similar to the recent study byDeng et al (2022). The results from numerical simulations with hygroscopicity indicate the activation of smaller droplets, which may help for the cloud invigoration by uplifting below freezing level due to strong updraft and influence rain intensity.…”

Water Solubility Distribution of Organic Matter Accounts for the Discrepancy in Hygroscopicity among Sub- and Supersaturated Humidity Regimes

“…The calibrated RH values were 81 ± 0.15, 87 ± 0.25, and 94 ± 0.18% for the set of mosquito coil samples and 82 ± 0.17, 88 ± 0.26, and 93 ± 0.22% for the set of tropical peat samples. Further details about HTDMA are presented by Deng et al…”

“…The generated particles passed through two diffusion dryers filled with activated charcoal (granular 6–10 mm, Wako Pure Chemical Industries) and silica gel for removing the remaining solvents (methanol and 1-octanol) in the particles. The particles were introduced to the high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS, Aerodyne Research), hygroscopicity tandem differential mobility analyzer (HTDMA), , and cloud condensation nuclei counter (CCNC, Droplet Measurement Technologies) for further analyses (Figure S3).…”

“…Classification of water-soluble OM (WSOM) and water-insoluble OM (WISOM) has long been employed for investigating the role of water solubility on hygroscopic growth and CCN activity. − WSOM is operationally defined as part of OM that can be extracted by water. , A typical range of water solubility for WSOM varies from 10 –10 to 1 g cm –3 . Theoretical analysis of the Köhler theory considering water solubility suggested that the water solubility of OM needs to be higher than 10 –4 g cm –3 for contributing to CCN activation and that OM with water solubility in the range of 10 –4 –10 –1 g cm –3 is especially critical for CCN activation. , In the case of OM that contains both highly and poorly water-soluble compounds, LLPS plays an important role during the hygroscopic growth process, meaning that the volume fractions of hydrophilic and hydrophobic phases change with RH .…”