ACETONE-PAN: Peroxyacetyl Nitrate and Acetone in the Upper Troposphere: MIPAS Satellite Retrievals and 3D Model Studies
Principal Investigator: Prof Martyn Chipperfield
Co-Investigators: Dr Steve Arnold and Dr Nigel Richards
Sponsor: NERC
Start Date: 1 February 2007
End Date: 31 January 2009
Value to Leeds: £96,800.07
Description
The direct observation of tropospheric composition from space is difficult, though in principle such observations can provide a wealth of new data to test and improve models. This project is a collaboration between the Earth observation group at the University of Leicester (PI: J. Remedios) and the global chemical modelling group in ICAS.
This project studies the distribution of acetone and peroxyacetyl nitrate (PAN) in the upper troposphere (UT) above ~8 km. Acetone is believed to be important in the UT HOx (OH + HO 2) budget. Its photolysis leads to the production of PAN which is a marker of coupled NOx/organic chemistry and plays a key role in O 3 production. Studying both acetone and PAN allows our understanding of these key organic species to be tested more comprehensively than studies of either in isolation.
In this study, concentrations of acetone and PAN are being retrieved from infrared measurements recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) which is currently in orbit on the ENVISAT satellite Recent Leicester work has shown, for the first time, that these compounds are detectable in MIPAS spectra and that, with suitable averaging if necessary, these species are retrievable with an accuracy useful for testing photochemical (chemical-transport) models. These new satellite retrievals will be the first global observations of PAN and acetone, and provide seasonal and latitudinal variations, including the effects of regional enhancements due to transport and uplift processes. They will also fill in the gaps in coverage from existing datasets from sparse aircraft campaigns, include remote regions such as the southern hemisphere (SH) UT, and confirm regional characteristics observed in those campaigns.
Acetone and PAN are important coupled components of the UT organic fraction. However, there is currently considerable uncertainty in the processes which control the abundance of acetone. Models are also untested with respect to the global distribution of PAN and reliant on aircraft comparisons in particular regions with biased sampling dependent on campaign objectives. We will compare the new MIPAS observations with simulations from the TOMCAT 3D chemical transport model (CTM). These will distinguish the relative importance of different processes affecting acetone and PAN. By comparing the seasonal/latitudinal variations, as well as the absolute abundance, we will estimate the best model fit to the data and distinguish, for example, between the role for a much slower photolysis loss of acetone versus a proposed ocean source.
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