TY - JOUR
T1 - Chemical characteristics of cloud water and the impacts on aerosol properties at a subtropical mountain site in Hong Kong SAR
AU - Li, Tao
AU - Wang, Zhe
AU - Wang, Yaru
AU - Wu, Chen
AU - Liang, Yiheng
AU - Xia, Men
AU - Yu, Chuan
AU - Yun, Hui
AU - Wang, Weihao
AU - Wang, Yan
AU - Guo, Jia
AU - Herrmann, Hartmut
AU - Wang, Tao
PY - 2020/1/13
Y1 - 2020/1/13
N2 - To investigate the cloud water chemistry and the effects of cloud processing on aerosol properties, comprehensive field observations of cloud water, aerosols, and gasphase species were conducted at a mountaintop site in Hong Kong SAR in October and November 2016. The chemical composition of cloud water including water-soluble ions, dissolved organic matter (DOM), carbonyl compounds (refer to aldehydes and acetone), carboxylic acids, and trace metals was quantified. The measured cloud water was very acidic with a mean pH of 3.63, as the ammonium (174 μeq L-1) was insufficient for neutralizing the dominant sulfate (231 μeq L-1) and nitrate (160 μeq L-1). Substantial DOM (9.3 mgC L-1) was found in cloud water, with carbonyl compounds and carboxylic acids accounting for 18% and 6% in carbon molar concentrations, respectively. Different from previous observations, concentrations of methylglyoxal (19.1 μM; μM is equal to μmol L-1) and glyoxal (6.72 μM) were higher than that of formaldehyde (1.59 μM). The partitioning of carbonyls between cloud water and the gas phase was also investigated. The measured aqueous fractions of dicarbonyls were comparable to the theoretical estimations, while significant aqueous-phase supersaturation was found for less soluble monocarbonyls. Both organics and sulfate were significantly produced in cloud water, and the aqueous formation of organics was more enhanced by photochemistry and under less acidic conditions. Moreover, elevated sulfate and organics were measured in the cloudprocessed aerosols, and they were expected to contribute largely to the increase in droplet-mode aerosol mass fraction. This study demonstrates the significant role of clouds in altering the chemical compositions and physical properties of aerosols via scavenging and aqueous chemical processing, providing valuable information about gas-cloud-aerosol interactions in subtropical and coastal regions.
AB - To investigate the cloud water chemistry and the effects of cloud processing on aerosol properties, comprehensive field observations of cloud water, aerosols, and gasphase species were conducted at a mountaintop site in Hong Kong SAR in October and November 2016. The chemical composition of cloud water including water-soluble ions, dissolved organic matter (DOM), carbonyl compounds (refer to aldehydes and acetone), carboxylic acids, and trace metals was quantified. The measured cloud water was very acidic with a mean pH of 3.63, as the ammonium (174 μeq L-1) was insufficient for neutralizing the dominant sulfate (231 μeq L-1) and nitrate (160 μeq L-1). Substantial DOM (9.3 mgC L-1) was found in cloud water, with carbonyl compounds and carboxylic acids accounting for 18% and 6% in carbon molar concentrations, respectively. Different from previous observations, concentrations of methylglyoxal (19.1 μM; μM is equal to μmol L-1) and glyoxal (6.72 μM) were higher than that of formaldehyde (1.59 μM). The partitioning of carbonyls between cloud water and the gas phase was also investigated. The measured aqueous fractions of dicarbonyls were comparable to the theoretical estimations, while significant aqueous-phase supersaturation was found for less soluble monocarbonyls. Both organics and sulfate were significantly produced in cloud water, and the aqueous formation of organics was more enhanced by photochemistry and under less acidic conditions. Moreover, elevated sulfate and organics were measured in the cloudprocessed aerosols, and they were expected to contribute largely to the increase in droplet-mode aerosol mass fraction. This study demonstrates the significant role of clouds in altering the chemical compositions and physical properties of aerosols via scavenging and aqueous chemical processing, providing valuable information about gas-cloud-aerosol interactions in subtropical and coastal regions.
UR - http://www.scopus.com/inward/record.url?scp=85078226330&partnerID=8YFLogxK
U2 - 10.5194/acp-20-391-2020
DO - 10.5194/acp-20-391-2020
M3 - Journal article
AN - SCOPUS:85078226330
SN - 1680-7316
VL - 20
SP - 391
EP - 407
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
IS - 1
ER -