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Long-term atmospheric measurements of C"1-C"5 alkyl nitrates in the Pearl River Delta region of southeast China [An article from: Atmospheric Environment]
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PublisherElsevier
ISBN / ASINB000RR7YPA
ISBN-13978B000RR7YP1
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Mixing ratios of seven C"1-C"5 alkyl nitrates (RONO"2) were measured during a 16-month study (August 2001-December 2002) at Tai O, a coastal site 30km west of central Hong Kong in the Pearl River Delta, the fastest-growing industrial region in the world. The C"3-C"4 (rather than C"1-C"2) RONO"2 were most abundant throughout the study, showing the importance of photochemical (rather than marine) RONO"2 production in the sampled air. A lack of methyl nitrate (MeONO"2) enhancement during summer, when the prevailing winds are from the ocean, indicates that the South China Sea is not a region of strong RONO"2 emissions. By contrast, MeONO"2 levels during pollution episodes (up to 25 parts per trillion by volume (pptv)) were the highest that our group has recorded during urban photochemical RONO"2 production, as opposed to marine emissions or biomass burning. The highest summed RONO"2 level of the study (204pptv) was measured in the afternoon of 7 November 2002, during an intense pollution episode that captured the highest ozone (O"3) level ever recorded in Hong Kong (203ppbv). During pollution episodes, the average ratio of O"3 to summed RONO"2 was roughly 1000:1 in freshly polluted air (ethyne/CO~3-5pptv/ppbv) and 500:1 in very freshly polluted air (ethyne/CO~6-8pptv/ppbv). Ozone and RONO"2 share a common photochemical source, and their good correlation in pollution plumes shows that RONO"2 can be used as a tracer of photochemical O"3 production. Even MeONO"2 showed similar diurnal variations as the C"2-C"5 RONO"2, indicating a strong photochemical source despite its very slow photochemical production from methane oxidation. The decomposition of longer-chain alkoxy radicals also does not explain the high MeONO"2 levels, and rough calculations show that methoxy radical reaction with NO"2 appears to be a viable alternate pathway for MeONO"2 production in polluted atmospheres, though further measurements and modeling are required to confirm this mechanism.
Description:
Mixing ratios of seven C"1-C"5 alkyl nitrates (RONO"2) were measured during a 16-month study (August 2001-December 2002) at Tai O, a coastal site 30km west of central Hong Kong in the Pearl River Delta, the fastest-growing industrial region in the world. The C"3-C"4 (rather than C"1-C"2) RONO"2 were most abundant throughout the study, showing the importance of photochemical (rather than marine) RONO"2 production in the sampled air. A lack of methyl nitrate (MeONO"2) enhancement during summer, when the prevailing winds are from the ocean, indicates that the South China Sea is not a region of strong RONO"2 emissions. By contrast, MeONO"2 levels during pollution episodes (up to 25 parts per trillion by volume (pptv)) were the highest that our group has recorded during urban photochemical RONO"2 production, as opposed to marine emissions or biomass burning. The highest summed RONO"2 level of the study (204pptv) was measured in the afternoon of 7 November 2002, during an intense pollution episode that captured the highest ozone (O"3) level ever recorded in Hong Kong (203ppbv). During pollution episodes, the average ratio of O"3 to summed RONO"2 was roughly 1000:1 in freshly polluted air (ethyne/CO~3-5pptv/ppbv) and 500:1 in very freshly polluted air (ethyne/CO~6-8pptv/ppbv). Ozone and RONO"2 share a common photochemical source, and their good correlation in pollution plumes shows that RONO"2 can be used as a tracer of photochemical O"3 production. Even MeONO"2 showed similar diurnal variations as the C"2-C"5 RONO"2, indicating a strong photochemical source despite its very slow photochemical production from methane oxidation. The decomposition of longer-chain alkoxy radicals also does not explain the high MeONO"2 levels, and rough calculations show that methoxy radical reaction with NO"2 appears to be a viable alternate pathway for MeONO"2 production in polluted atmospheres, though further measurements and modeling are required to confirm this mechanism.
