Fast heterogeneous loss of N2O5 leads to significant nighttime NOx removal and nitrate aerosol formation at a coastal background environment of southern China.

Nitrate radical (NO 3) and dinitrogen pentoxide (N 2 O 5) play crucial roles in the nocturnal atmosphere. To quantify their impacts, we deployed a thermal-dissociation chemical ionization mass spectrometry (TD-CIMS), to measure their concentration, as well as ClNO 2 at a coastal background site in the southern of China during the late autumn of 2012. Moderate levels of NO 3 , N 2 O 5 and high concentration of ClNO 2 were observed during the study period, indicating active NO x -O 3 chemistry in the region. Distinct features of NO 3 , N 2 O 5 and ClNO 2 mixing ratios were observed in different airmasses. Further analysis revealed that the N 2 O 5 heterogeneous reaction was the dominant loss of N 2 O 5 and NO 3 , which showed higher loss rate compared to that in other coastal sites. Especially, the N 2 O 5 loss rates could reach up to 0.0139 s−1 when airmasses went across the sea. The fast heterogeneous loss of N 2 O 5 led to rapid NO x loss which could be comparable to the daytime process through NO 2 oxidization by OH, and on the other hand, to rapid nitrate aerosol formation. In summary, our results revealed that the N 2 O 5 hydrolysis could play significant roles in regulating the air quality by reducing NO x but forming nitrate aerosols. Unlabelled Image • N 2 O 5 and NO 3 were observed with distinct features in different airmasses. • The fast hydrolysis of N 2 O 5 dominated the loss of N 2 O 5 and NO 3 , particularly when continental air went across the sea. • The fast loss of N 2 O 5 can contribute to a significant fraction of NO x removal and nitrate aerosol formation. [ABSTRACT FROM AUTHOR]