A34F-05
Observations of Nitryl Chloride and Modeling its Source and Effect on Ozone in the Planetary Boundary Layer of Southern China
Wednesday, 16 December 2015: 17:00
3010 (Moscone West)
Tao Wang1, Yee Jun Tham2, Likun Xue3, Qinyi LI1, Qiaozhi Zha4, Zhe Wang4, Steven Poon4, Steven S Brown5, William P Dube5, Peter K. K. Louie6, Connie Luk7, Donald Ray Blake8 and Wilson Tsui9, (1)Hong Kong Polytechnic University, Department of Civil and Environmental Engineering, Hong Kong, Hong Kong, (2)Hong Kong Polytechnic University, Hong Kong, Hong Kong, (3)Shandong University, Environment Research Institute, Jinan, China, (4)Hong Kong Polytechnic University, Department of Civil and Environmental Engineering, Hong Kong, China, (5)NOAA Boulder, Boulder, CO, United States, (6)Hong Kong Environmental Protection Department, Hong Kong, China, (7)Environmental Protection Department, Hong Kong, China, (8)University of California Irvine, Irvine, CA, United States, (9)PTC International limited, Hong Kong, China
Abstract:
Nitryl chloride (ClNO2) is produced from heterogeneous reaction of N2O5 on chloride-containing aerosol. ClNO2 can impact the oxidative capacity of the atmosphere by production of highly reactive chlorine radical (Cl) and recycling NOx after its photolysis. Subsequent reactions between Cl and volatile organic compounds may enhance photochemical formation of ozone. Despite the potentially important roles of ClNO2 in atmospheric chemistry, its abundance and effect are not well understood in some parts of the world. In late autumn 2013, ClNO2 was measured with a chemical ionization mass spectrometer (CIMS) at a mountain top (957 m a.s.l) in Hong Kong. During 12 nights with continuous CIMS data, elevated concentrations of ClNO2 (>400 ppbv) or its precursor N2O5 (>1000 pptv) were observed on six nights, with the highest ever reported ClNO2 (4.7 ppbv) and N2O5 (7.7 ppbv) in one case. Backward particle dispersion calculations driven by winds simulated with a mesoscale meteorological model show that the ClNO2/N2O5-laden air at the high-elevation site was due to transport of urban/industrial pollution north of the site. The highest ClNO2/N2O5 case was observed in a later period of the night and was characterized with extensively processed air and with the presence of non-oceanic chloride. A chemical box model with detailed chlorine chemistry was used to assess the possible impact of the ClNO2 in the well-processed regional plume on next-day ozone as the air mass continued to downwind locations. The results show that the ClNO2 could enhance ozone up to 23 ppbv or a 22% increase at the ozone peak in the following day. This study demonstrates the importance of the ClNO2 chemistry in polluted environments and highlights the need to consider this process in photochemical models for prediction of ground-level ozone and haze.
