Nocturnal odd‐oxygen budget and its implications for ozone loss in the lower troposphere

Nitrogen oxides are important to the regulation of ozone throughout the Earth's atmosphere. Of particular interest for regional air quality is photochemical production and nocturnal destruction of O 3 in the lower troposphere in high NO x (=NO + NO 2 ) environments. Nocturnal tropospheric odd oxygen (O x ), defined as O 3 + NO 2 + 2NO 3 + 3N 2 O 5 , is used to assess the impact of NO x emissions on nocturnal O 3 loss. Recent aircraft measurements of the components of O x and HNO 3 yield a detailed accounting of the nocturnal O x budget in a regionally polluted environment. The analysis demonstrates the role of NO 3 and N 2 O 5 reactions in nocturnal O 3 destruction and shows that multiple factors, including timing of NO x emissions, hydrocarbon and aerosol loading, seasonality and atmospheric mixing, govern the impact of NO x emissions on regional‐scale air quality.