Towards New Constraints on the Tropical Ozone Budget: Interannual Variability in Peroxyacetyl Nitrate (PAN) Observations from the Aura Tropospheric Emission Spectrometer

Abstract:

Peroxyacetyl nitrate (PAN) is a thermally unstable reservoir for NO_x that allows NO_x to be transported large distances, enabling ozone formation far downwind from the original source. Sources of PAN precursors include anthropogenic combustion, biomass burning, lightning and biogenic emissions. PAN chemistry plays a key role in determining the global ozone distribution. Until now, available measurements have been sparse and generally limited to intensive field campaigns.

The Tropospheric Emission Spectrometer (TES), flying on the NASA Aura satellite, provides measurements of a range of trace gases that have spectral features in the thermal infrared, including ozone (O₃), carbon monoxide (CO) and PAN. PAN can be retrieved from TES spectra for cases where the volume mixing ratio is above ~0.2 ppbv [Payne et al., 2014].

In this work, we present TES retrievals of PAN and CO in the tropics over the ten-year lifetime of the Aura mission. The TES PAN dataset offers an unprecedented insight into the inter-annual variability of PAN in the tropics. We compare TES retrievals of PAN, CO and O₃ in the tropics to simulations from the GEOS-Chem global chemical transport model for austral spring (peak burning season) of selected years. In the tropics, GEOS-Chem predicts that the dominant sources of PAN are biomass burning and lightning. The version of GEOS-Chem used in this work has been specifically updated to improve the simulation of PAN [Fischer et al., 2014]. Similarities and differences between the TES measurements and the GEOS-Chem simulations are used to infer causes of inter-annual variability of tropical ozone.

References:

E. V. Fischer et al., Atmospheric peroxyacetyl nitrate (PAN): a global budget and source attribution, Atmos. Chem. Phys., 14, 2679-2698, 2014

V. H. Payne et al., Satellite observations of peroxyacetyl nitrate from the Aura Tropospheric Emission Spectrometer, Atmos. Meas. Tech. Discuss., 7, 5347-5379, 2014