Inferring the lifetime of NOx and aerosol from space based observations

Observations of urban NO₂ and aerosol from space are often used as constraints on emissions. However, the observed burden is also strongly modulated by secondary chemistry and deposition. We explore novel approaches to using space based observations as a constraint on secondary chemistry and removal. For NO_x, we explore the effects of the chemistry of peroxyacetyl nitrate (PAN) while for aerosol we examine secondary production. We explore these ideas in the context of decadal trends in urban OH that we have inferred from space-based NO₂ observations. We also compare the observations to predictions of numerical models.