Towards New Constraints on Ozone Production from Lightning NOx via Satellite Measurements of Peroxyacetyl Nitrate (PAN)

Abstract:

Quantifying the strength and distribution of the source of nitrogen oxide radicals (NO_x) from lightning, and the impact of this source on tropospheric ozone, is critical to understanding the contribution of anthropogenic vs natural sources of ozone as well as feedbacks between climate change and atmospheric chemistry. In the presence of biogenic volatile organic compounds, lightning NO_x may be converted to peroxyacetyl nitrate (PAN). PAN formation acts to sequester NOx and decrease ozone formation, thereby playing an important role in determining the oxidation capacity of the troposphere. However, comprehensive in situ measurements of reactive nitrogen species in the upper troposphere are insufficient for the purpose of validation of the representation of the relevant processes in chemical transport models.

New satellite measurements of PAN from the Aura Tropospheric Emission Spectrometer (TES) provide an opportunity to place new constraints on the influence of lightning NO_x on ozone production. Here we show that TES provides direct observations of enhanced PAN concentrations downwind of convective events over the US in summertime, evaluate the ability of the GEOS-Chem model to reproduce these enhancements and quantify the reduction in ozone formation that would result from the observed PAN. We will also discuss the prospects for PAN retrievals from other nadir-viewing satellite instruments.