Observation of Nitrate Radical in the Nocturnal Boundary Layer During a Summer Field Campaign in Pearl River Delta, China

From July 4 to 11, 2006 at Back Garden site (23 degrees 28'86 '' N; 113 degrees 02'91 '' E), nighttime nitrate radical (NO3) was measured with a long path differential optical absorption spectroscopy (DOAS) during an intensive field campaign in the Pearl River Delta of China. The NO3 concentration in polluted air masses varied from 3.6 to 82.5 ppt with an average level of 21.8 +/- 1.8 ppt. NO3 at these levels can play a significant role in oxidation of volatile organic compounds (VOCs). The calculated production rate of nitrate radical ranged from 8 x 10(5) to 2.98 x 10(7) cm(-3) s(-1), while its lifetimes spanned from between just several seconds to 650 seconds, with an average of 89 seconds. N2O5 levels were calculated with the average of 620 +/- 93 ppt during this campaign. The possible scavenging processes for the nitrate radical were obtained by using a statistical analysis of the correlation between NO3 and NO levels, NO3 concentration and its production rate, and the NO3 lifetime and NO2 levels, respectively. Results showed that the direct losses were of importance at Back Garden in summer Pearl River Delta, China.