Measurements of nocturnal nitrogen oxides in the Lower Fraser Valley of British Columbia, Canada
Abstract
It is well established that nitrogen dioxide (NO2) is oxidized at night by ozone (O3) to produce the nitrate radical (NO3) and dinitrogen pentoxide (N2O5). Reaction of N2O5 on aerosol surfaces produces mainly nitric acid (HNO3), whose deposition removes nitrogen oxides (NOx = NO + NO2) from the atmosphere. In the presence of aerosol chloride, however, N2O5 can convert to the NOx reservoir species nitryl chloride (ClNO2). The main fate of ClNO2 is photolysis (after sunrise), which produces chlorine radicals and regenerates NO2. If efficient, the nocturnal formation of ClNO2 can extend the effective lifetime of nitrogen oxides, which can impact air quality. Here, ambient measurements of NO2, NO3, and N2O5 (by cavity ring-down spectroscopy) and ClNO2 (by iodide ion chemical ionization mass spectrometry) in the Lower Fraser Valley of British Columbia are presented. The study was conducted near the Abbotsford International Airport, which is located approximately 35 km from the Pacific Ocean, from 20 Jul to 4 Aug, 2012. At night, O3 was titrated relatively quickly, rationalized by formation of a shallow surface layer and rapid surface deposition. The low nocturnal O3 mixing ratios limited the extent of nocturnal nitrogen oxide chemistry. Mixing ratios of ClNO2 generally peaked 1 - 2 hours after sunrise following the break-up of the nocturnal surface layer. This suggests that ClNO2 formed more efficiently in the residual layer aloft than at the surface.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A13D0240O
- Keywords:
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- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE Troposphere: composition and chemistry;
- 0394 ATMOSPHERIC COMPOSITION AND STRUCTURE Instruments and techniques