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

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 CH, CH, CH, CH, and CH 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 (±0.2× 10), respectively. Enhancements of NO, were variable, averaging 0.0056 (± 0.0030) mole NO/mole CO, while perturbations of NO were very small, usually undetectable. At least 1/3 of the NO in the haze layers had been converted to peroxyacetyl nitrate (PAN), representing a potential source of NO to the global atmosphere; much of the balance was oxidized to nitrate (HNO and paniculate). The composition of sub‐Arctic haze layers was consistent with aged emissions from smoldering combustion, except for CH, which appears to be partly biogenic. Inputs from the stratosphere and from biomass fires contributed major fractions of the NO in the remote sub‐Arctic troposphere. Analysis of aircraft and ground data indicates relatively little influence from mid‐latitude industrial NO in this region during summer, possibly excepting transport of PAN. Production of O was inefficient in sub‐Arctic haze layers, less than 0.1 O molecules per molecule of CO, reflecting the low NO/CO emission ratios from smoldering combustion. Mid‐latitude pollution produced much more O, 0.3 – 0.5 O molecules per molecule of CO, a consequence of higher NO/CO emission ratios.