Origin of tropospheric NO{sub x} over subarctic eastern Canada in summer
- Harvard Univ., Cambridge, MA (United States)
- Georgia Institute of Technology, Atlanta, GA (United States)
- Univ. of California, Irvine, CA (United States)
- NASA Ames Research Center, Moffett Field, CA (United States)
- Univ. of New Hampshire, Durham, NH (United States)
- NASA Langley Research Center, Hampton, VA (United States)
The origin of NO{sub x} in the summertime troposphere over subarctic eastern Canada is investigated by photochemical modeling of aircraft and ground-based measurements from the Arctic Boundary Layer Expedition (ABLE 3B). It is found that decomposition of peroxyacetyl nitrate (PAN) can account for most of the NO{sub x} observed between the surface and 6.2 km altitude (aircraft ceiling). Forest fires represent the principal source of PAN in the region, implying the same origin for NO{sub x}. There is, however, evidence for an unidentified source of NO{sub x} in occasional air masses subsiding from the upper troposphere. Isoprene emissions from boreal forests maintain high NO{sub x} concentrations in the continental boundary layer over eastern Canada by scavenging OH and NO{sub 3}, thus slowing down conversion of NO{sub x} to HNO{sub 3}, both in the daytime and at night. This effect is partly compensated by the production of CH{sub 3}CO{sub 3} radicals during isoprene oxidation, which slows down the decomposition of PAN subsiding from the free troposphere. The peroxy radical concentrations estimated from concurrent measurements of NO and NO{sub 2} concentrations during ABLE 3B are consistent with values computed from our photochemical model below 4 km, but model values are low at higher altitudes. The discrepancy may reflect either a missing radical source in the model or interferences in the NO{sub 2} measurement. 63 refs., 10 figs., 1 tab.
- OSTI ID:
- 98852
- Journal Information:
- Journal of Geophysical Research, Vol. 99, Issue D8; Other Information: PBD: 20 Aug 1994
- Country of Publication:
- United States
- Language:
- English
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