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 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.