Fast heterogeneous loss of N 2 O 5 leads to significant nighttime NO x removal and nitrate aerosol formation at a coastal background environment of southern China

Nitrate radical (NO ) and dinitrogen pentoxide (N O ) 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 at a coastal background site in the southern of China during the late autumn of 2012. Moderate levels of NO , N O and high concentration of ClNO were observed during the study period, indicating active NO -O chemistry in the region. Distinct features of NO , N O and ClNO mixing ratios were observed in different airmasses. Further analysis revealed that the N O heterogeneous reaction was the dominant loss of N O and NO , which showed higher loss rate compared to that in other coastal sites. Especially, the N O loss rates could reach up to 0.0139 s when airmasses went across the sea. The fast heterogeneous loss of N O led to rapid NO loss which could be comparable to the daytime process through NO oxidization by OH, and on the other hand, to rapid nitrate aerosol formation. In summary, our results revealed that the N O hydrolysis could play significant roles in regulating the air quality by reducing NO but forming nitrate aerosols.