Atmospheric chemistry in the Arctic and subarctic: Influence of natural fires, industrial emissions, and stratospheric inputs

Authors

  • S. C. Wofsy,

  • G. W. Sachse,

  • G. L. Gregory,

  • D. R. Blake,

  • J. D. Bradshaw,

  • S. T. Sandholm,

  • H. B. Singh,

  • J. A. Barrick,

  • R. C. Harriss,

  • R. W. Talbot,

  • M. A. Shipham,

  • E. V. Browell,

  • D. J. Jacob,

  • J. A. Logan


Abstract

Haze layers with perturbed concentrations of trace gases, believed to originate from tundra and forest wild fires, were observed over extensive areas of Alaska and Canada in 1988. Enhancements of CH4, C2H2, C2H6, C3H8, and C4H10 were linearly correlated with CO in haze layers, with mean ratios (mole hydrocarbon/mole CO) of 0.18 (± 0.04 (1 σ)), 0.0019 (± 0.0001), 0.0055 (± 0.0002), 0.0008 (± 0.0001), and 1.2 × 10−4 (±0.2× 10−4), respectively. Enhancements of NOy, were variable, averaging 0.0056 (± 0.0030) mole NOy/mole CO, while perturbations of NOx were very small, usually undetectable. At least 1/3 of the NOy in the haze layers had been converted to peroxyacetyl nitrate (PAN), representing a potential source of NOx to the global atmosphere; much of the balance was oxidized to nitrate (HNO3 and paniculate). The composition of sub-Arctic haze layers was consistent with aged emissions from smoldering combustion, except for CH4, which appears to be partly biogenic. Inputs from the stratosphere and from biomass fires contributed major fractions of the NOy in the remote sub-Arctic troposphere. Analysis of aircraft and ground data indicates relatively little influence from mid-latitude industrial NOy in this region during summer, possibly excepting transport of PAN. Production of O3 was inefficient in sub-Arctic haze layers, less than 0.1 O3 molecules per molecule of CO, reflecting the low NOx/CO emission ratios from smoldering combustion. Mid-latitude pollution produced much more O3, 0.3 – 0.5 O3 molecules per molecule of CO, a consequence of higher NOx/CO emission ratios.

Ancillary