Observation of ambient NO3 radicals by LP-DOAS at a rural site in North China Plain

Abstract

NO3 radicals can clean the atmospheric primary contaminants during the night. However, it can also effect the formation of secondary organic aerosol (SOA) and nitrate, which may worsen air quality. We report field observations of NO3 radicals with a home-made long path differential optical absorption spectroscopy (LP-DOAS) at a rural site in the polluted North China Plain in the summer of 2014. The detection limit (1σ) of NO3 with 3.4 km optical path was 3.4 ppt. The observed mean NO3 mixing ratios were 21 ppt with the maximum value of 104 ppt. The average calculated production rates and steady state lifetime of NO3 were 952 ppt/h and 103 s, respectively. The increase of both PM2.5 (>60 μg/m3) and RH (>60%) would result in an increase of the loss of NO3. The proportion of indirect losses rise with the increase of RH (>50%). The fitting kNO3 ranged from 0.0018 to 0.012 s−1 while γN2O5 was 0.0012 to 0.072. The ratios of direct loss ranged from 20.95% to 90.36% with an average of 56.81% during the campaign.