Hygroscopic properties of water-soluble matter and humic-like organics in atmospheric fine aerosol

[摘要] Ambient continental-rural fine aerosol(K-puszta, Hungary, PM_1.5) was sampled on quartz fibre filters in winter andsummer 2001. Water-soluble matter (WSM) was extracted in MilliQ-water, and, in a second step, solid phase extraction wasused to isolate the less hydrophilic fraction (ISOM) of the water-soluble organic matter (WSOM) from remaining inorganic saltsand "most" hydrophilic organic matter (MHOM). This approach allowed ISOM, which constitutes the major fraction of WSOM, to beisolated from ambient aerosols and investigated in pure form. Hygroscopic properties of both WSM and ISOM extracts as well as ofaquatic reference fulvic and humic acids were investigated using a Hygroscopicity Tandem Differential Mobility Analyser(H-TDMA). ISOM deliquesced between 30% and 60% relative humidity (RH), andhygroscopic growth factors at 90% RH ranged from 1.08 to 1.17. The hygroscopicity of ISOM is comparable to secondary organicaerosols obtained in smog chamber experiments, but lower than the hygroscopicity of highly soluble organic acids. The hygroscopicbehaviour of investigated fulvic and humic acids had similarities to ISOM, but hygroscopic growth factors were slightly smaller anddeliquescence was observed at higher RH (75-85% and 85-95% RH for fulvic acid and humic acid, respectively). These differencesprobably originate from larger average molecular mass and lower solubility of fulvic and humic acids.

Inorganic composition data, measured ISOM hygroscopicity, and a presumed value for the hygroscopicity of the small remaining MHOMfraction were used to predict hygroscopic growth of WSM extracts. Good agreement between model prediction and measured water uptakewas observed with differences (by volume) ranging from +1% to -18%. While deliquescence properties of WSM extracts weremainly determined by the inorganic salts (42-53 wt % of WSM), the WSOM accounted for a significant fraction of particulatewater. At 90% RH, according to model predictions and measurements, about80-62% of particulate water in the samples are associated with inorganic salts and about20-38% with WSOM. The relative contributions of both distinguished WSOM fractions,ISOM and MHOM, remains uncertain since MHOM was not available in isolated form, but the results suggest that the less abundant MHOMis also important due to its presumably larger hygroscopicity.

[学科分类] 大气科学