title: [Low-molecular-weight organic acids in precipitation in Zunyi City, Guizhou province].
abstract: Formic (HCOOH) and acetic (CH3COOH) acids are ubiquitous in troposphere. Studies on the low-molecular carboxylic acids help shed light on the biogeochemical cycles of carbon, hydrogen and oxygen, as well as on the formation of acid precipitation. As a city with severe acid precipitation, the city Zunyi in north Guizhou province, provide a typical background for gaining insight into the organic geochemistry in the heavily polluted atmospheric environment. We collected the precipitation in the downtown city for a whole year on the event basis, and measured inorganic and organic anions with ion chromatograph and cations with atomic absorption spectroscopy. The data demonstrate an annual average pH of 4.11, a clear indication of the acid atmosphere. The volume-weighted mean concentrations of [HCOO-]T and [CH3COO-]T were 9.29 micromol x L(-1) (ranged from 0.15 micromol x L(-1) to 46.14 micromol x L(-1)) and 6.47 micromol x L(-1) (ranged from 0.02 micromol x L(-1) to 19.11 micromol x L(-1)) respectively, accounting for 4.10% of the total anions. With a coefficient of 0.86, formic is significantly correlated with acetic acid, suggesting that both acids share common sources. The acids often decrease with time in a precipitation event, with occasional increases in the middle and last stages, indicating that the organic acids are primarily scavenged from blow cloud, with limited amount from the long distance transportation. The close range provenance of organic acids is facilitated by the local environmental condition, which is characterized by the mountain-enclosed valley with high humidity, low wind speed, and high atmospheric dust content. Based on the Henry's Law, we proposed the ratio of formic and acetic acids in the precipitation (F/A)aq as the indicator of the sources, and thus found that the anthropogenic sources are responsible for the organic compounds in the Spring and Winter, while vegetation emissions claim the sources in the Summer and Autumn.
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China. jiangwei8255@gmail.com
authors.forename: Wei
authors.initials: W
authors.lastname: Jiang
authors.forename: Xin-qing
authors.initials: XQ
authors.lastname: Lee
authors.forename: Yong
authors.initials: Y
authors.lastname: Zeng
authors.forename: Rong-sheng
authors.initials: RS
authors.lastname: Huang
authors.forename: Ling
authors.initials: L
authors.lastname: Tan
authors.forename: Gang
authors.initials: G
authors.lastname: Xu
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
mesh_terms: D019342:Acetic Acid / Q000032:analysis*; D015258:Acid Rain / Q000032:analysis*; D000393:Air Pollutants / Q000032:analysis*; D002681:China; D004784:Environmental Monitoring; D005561:Formates / Q000032:analysis*; D009930:Organic Chemicals / Q000032:analysis; D011891:Rain
chemical_list: D015258:Acid Rain; D000393:Air Pollutants; D005561:Formates; D009930:Organic Chemicals; C030544:formic acid; D019342:Acetic Acid