Previous zero-dimensional photochemical calculations indicate that multiple tropospheric steady states may exist, in which different NOx(≡NO+NO2) levels could be supported by the same source of NOx. To investigate this possibility more closely, a one-dimensional photochemical model has been used to estimate the rate of removal of atmospheric NOx compounds at different NOx levels. At low NOx levels NOx is photochemically converted to HNO3, which is removed by either wet or dry deposition. At high NOx levels formation of HNO3 is inhibited, and NOx is removed by a variety of other processes, including rainout of N2O4 and N2O5, surface deposition of NO and NO2, and direct dissolution of NO and NO2 in rainwater. Multiple steady states are possible if surface deposition of NOx is relatively inefficient. The NOx source required to trigger high atmospheric NOx levels is approximately 10 to 15 times the present global emission rate-less than half the source strength predicted by the zero-dimensional model. NOx mixing ratios in excess of 10-7 would cause severe damage to the ozone layer and could result in either a climatic warming or cooling, depending upon the amount of NO2 present.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry
- Atmospheric Science