A budget analysis of NO x column losses over the Korean peninsula

Abstract

In this study, the chemical and physical losses of nitrogen oxides (NOx) over the Korean peninsula were discussed in order to better understand the effects of the NOx losses on the tropospheric NO2 columns. Initially, it was found that the physical loss processes due to dry and wet depositions had almost negligible impacts on the NOx loss processes over the Korean peninsula. In contrast, the hourly NOx chemical column losses were large at ∼1014 molecules cm−2 h−1. The amounts of NOx removed for 1 hour account for approximately 33–35% of the episode-averaged tropospheric NO2 columns during summer over the Korean peninsula. The NOx chemical column loss rates were 24.1–70.9 times larger than the NOx physical column loss rates. In a budget analysis of the NOx chemical column losses, HNO3 formation via the reaction of OH + NO2 had the largest contribution toward the NOx chemical losses (42–55% during fall and winter seasons; 76–77% during spring; 92–93% during summer). Large amounts of NOx were also removed by heterogeneous nitrate formation via N2O5 condensation during the cold seasons (42–56%) over the Korean peninsula. The columnar NOx chemical losses took place mainly due to the two chemico-physical reaction processes, and also showed seasonal variations. PAN (Peroxyacetyl Nitrate) is another NO2 reservoir of potential importance. If the influence of the PAN-related chemistry on the NOx budget is considered, it can result in an approximate 69% increase in the NOx chemical column loss during summer. Such increases in the amounts of NOx removed for 1 hour due to the formation of PAN were equivalent to 56–58% of the episode-averaged tropospheric NO2 columns during summer over the Korean peninsula. Such active NOx chemical losses during summer are another main factor for the tropospheric NO2 columns exhibiting their smallest values during summer.