Atmos. Chem. Phys. Discuss., 10, 21439-21474, 2010
www.atmos-chem-phys-discuss.net/10/21439/2010/
doi:10.5194/acpd-10-21439-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Anthropogenic imprints on nitrogen and oxygen isotopic composition of precipitation nitrate in a nitrogen-polluted city in southern China
Y. T. Fang1,2, K. Koba2, X. M. Wang3, D. Z. Wen1, J. Li1, Y. Takebayashi2, X. Y. Liu2, and M. Yoh2
1South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China
2Tokyo University of Agriculture and Technology, Tokyo 183 8509, Japan
3School of Environmental Sciences and Engineering, Sun Yat-Sen University, \newline Guangzhou 501275, China

Abstract. Nitric acid (HNO3) or nitrate (NO3) is the dominant sink for reactive nitrogen oxides (NOx = NO + NO2) in the atmosphere. In many Chinese cities, HNO3 is becoming a significant contributor to acid deposition. In the present study, we used the denitrifier method to measure nitrogen (N) and oxygen (O) isotopic composition of NO3 in 113 precipitation samples collected from Guangzhou City in southern China over a two-year period (2008 and 2009). We attempted to better understand the spatial and seasonal variability of atmospheric NOx sources and the NO3 formation pathways in this N-polluted city in the Pearl River Delta region. The δ15N values of NO3 (versus air N2) ranged from −4.9 to +10.1‰, and averaged +3.9‰ in 2008 and +3.3‰ in 2009. Positive δ15N values were observed throughout the year, indicating the anthropogenic contribution of NOx emissions, particularly from coal combustion. Different seasonal patterns of δ15N-NO3 were observed between 2008 and 2009, which might reflect different human activities associated with the global financial crisis and the intensive preparations for the 16th Asian Games. Nitrate δ18O values (versus Vienna Standard Mean Ocean Water) varied from +33.4 to +86.5‰ (average +65.0‰ and +67.0‰ in 2008 and 2009, respectively), a range being lower than those reported for high altitude and polar areas. Several δ18O values were observed lower than the expected minimum of 50‰ at our study site. This was likely caused by the reaction of NO with peroxy radicals; peroxy radicals can compete with O3 to convert NO to NO2, thereby donate O atoms with much lower δ18O value than that of O3 to atmospheric NO3. Our results highlight that the influence of human activities on atmospheric chemistry can be recorded by the N and O isotopic composition of atmospheric NO3 in a N-polluted city.

Citation: Fang, Y. T., Koba, K., Wang, X. M., Wen, D. Z., Li, J., Takebayashi, Y., Liu, X. Y., and Yoh, M.: Anthropogenic imprints on nitrogen and oxygen isotopic composition of precipitation nitrate in a nitrogen-polluted city in southern China, Atmos. Chem. Phys. Discuss., 10, 21439-21474, doi:10.5194/acpd-10-21439-2010, 2010.
 
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