A new mechanism for regional tropospheric chemistry modeling
- Fraunhofer Inst. for Atmospheric Environmental Research (IFU), Garmisch-Partenkirchen (Germany)
The authors present a new atmospheric chemical mechanism for the modeling of regional air pollution, the Regional Atmospheric Chemistry Mechanism (RACM). Ozone is produced through the photo-oxidation of nitrogen oxides and volatile organic compounds. The organic chemistry of the RACM mechanism is a significant improvement over existing mechanisms. Since the organic chemistry of the atmosphere is very complicated and computer resources are limited, the RACM mechanism uses grouped organic classes to describe atmospheric organic chemistry. The individual emitted organic species are aggregated into the 32 RACM classes through a reactivity weighting approach. The oxidation schemes of alkanes, alkenes and aromatics were reevaluated and improved through the use of new laboratory data. These improvements include a significant reduction in the ratio of aldehydes to ketones produced from alkanes; the production of relatively large amounts of nitrates from the reactions of unbranched alkenes with NO{sub 3}; the production of HO from alkene ozonolysis; a reduction of cresol production from the oxidation of aromatics and better treatment of unsaturated dicarbonyl species. The peroxyacetyl nitrate chemistry and the organic peroxy radical--peroxy radical reactions were revised which caused a significant reduction in predicted PAN concentrations. For biogenic species, a new isoprene scheme includes an improved representation of methacrolein, isoprene ozonolysis, hydroperoxide production and the carbonitrate production. The new RACM mechanism has been tested against smog chamber data. Predicted ozone profiles and the timing of the ozone peak are well within the uncertainties of experiments. The authors also discuss mechanism and laboratory data uncertainties, future data needs and new plans for the development of improved chemical mechanisms for air quality models.
- OSTI ID:
- 351051
- Report Number(s):
- CONF-970677--
- Country of Publication:
- United States
- Language:
- English
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