Influence of nocturnal vertical stability on daytime chemistry: A one-dimensional model study

Nocturnal chemistry can play an important role in determining the initial morning conditions for daytime chemistry in urban areas. However, the impact on daytime O-3 levels is difficult to assess as the suppression of vertical trace gas transport leads to highly altitude dependent nocturnal chemistry, in particular with respect to the removal and conversion of nitrogen oxides (NOx) and volatile organic compounds (VOC). One-dimensional (1-D) chemical transport model calculations for different nighttime vertical stabilities and different ozone formation regimes (i.e. NOx- vs. VOC-sensitive) were performed assuming a 1000 m high daytime boundary layer and a growing nocturnal boundary layer reaching 200 m height at the end of the night. Exclusion of NO3 chemistry from the model leads to daytime O-3 concentration changes from -4% to +16% for different O-3 sensitivities. In all cases strong nocturnal vertical concentration profiles of NOx, O-3, NO3 and N2O5 and a dependence of these profiles on vertical stability were found at night. The nocturnal NOx loss averaged over the lowest 1000 m changes by 9-24% for different vertical stabilities and ozone sensitivities. The impact of nocturnal vertical stability leads to 7-12% difference in O-3 concentration in the morning and similar to 0-2.5% in the afternoon. (C) 2010 Elsevier Ltd. All rights reserved.