Strong Seasonal Transition and Complex Sources of Volatile Organic Compounds at an Urban Site in Guangzhou, China

We report observations of non-methane volatile organic compounds (VOCs) at an urban site in Guangzhou, China, and analyzed the seasonally contrasting composition, diurnal patterns, and sources of VOCs driven by the Asian Monsoon weather. In July, southerly low-level jets and coastal recirculation coincided with a large enhancement of light alkanes and alkenes along with methyl tert-butyl ether from urban transportation. Diurnal profiles of propanal and methyl vinyl ketone followed isoprene and O₃, suggesting a common biogenic origin and fast photochemical production. In October, dominating northerly descending dry air mass led to a 10-fold increase in acetone and methyl ethyl ketone, suggesting a large free tropospheric reservoir and abundant precursors of these ketones. Enhanced source apportionment aided by a comprehensive emission speciation data set identified five classes of VOCs from a much larger pool of local and regional emission sources than reported from previous studies. Seasonal transition of VOCs offers unique natural constraint for the chemistry and sources of VOCs in this and other similar regions, which warrants future long term measurements and advanced modeling and analysis.