Observations of high rates of NO2-HONO [NO subscript 2 - HONO] conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal
Author(s)Yu, Y.; Galle, B.; Panday, Arnico K.; Hodson, Elke Lynn; Prinn, Ronald G.
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Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out in the Kathmandu urban atmosphere during January–February 2003, contributing to the sparse knowledge of nitrous acid in South Asia. The results showed average nocturnal levels of HONO (1.7±0.8 ppbv), NO2 [NO subscript 2] (17.9±10.2 ppbv), and PM10(0.18±0.11 mgm−3 [mg m superscript -3]) in urban air in Kathmandu. Surprisingly high ratios of chemically formed secondary [HONO] to [NO2] [NO subscript 2] (up to 30%) were found, which indicates unexpectedly efficient chemical conversion of NO2 [NO subscript 2] to HONO in Kathmandu. The ratios of [HONO]/[NO2] [NO subscript 2] at night were found to be much higher than previously reported values from measurements in urban air in Europe, North America and Asia. The influences of aerosol surface, ground reactive surface, and relative humidity on NO2-HONO [NO subscript 2 - HONO] chemical conversion were discussed. The high humidity, strong and low inversion layer at night, and high aerosol pollution burden in Kathmandu may explain the particularly efficient conversion of NO2 [NO subscript 2] to HONO.
DepartmentMassachusetts Institute of Technology. Center for Global Change Science; Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Atmospheric Chemistry and Physics
European Geosciences Union / Copernicus
Yu, Y. et al. “Observations of High Rates of NO2 [NO subscript 2]-HONO Conversion in the Nocturnal Atmospheric Boundary Layer in Kathmandu, Nepal.” Atmospheric Chemistry and Physics 9.17 (2009) : 6401-6415. © Author(s) 2009
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