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Dimethyl sulfide (DMS), sulfur dioxide, non-sea-salt sulfate, and various aerosol properties were measured during three field programs (two airborne and one ground-based) near Barrow and Deadhorse (Prudhoe Bay), Alaska. The two airborne sampling programs took place in spring and early summer, and the ground-based measurements spanned an entire summer. DMS concentrations in the Arctic atmosphere ranged from a few parts per trillion by volume (pptv) in spring and fall to higher values in summer (generally a few tens of pptv with occasional peaks of 100 to 300 pptv). In addition, DMS concentrations were measured during the spring near Resolute in seawater below the ice and in ice-algae and kelp cultures. The seawater samples taken from below the ice in spring had DMS concentrations comparable to those in other oceanic regions. Taken together, these measurements show that the Arctic Ocean is potentially a substantial source of DMS, which likely becomes important as sea ice melts in the early summer. Local atmospheric concentrations increased throughout the summer, peaking in August. In regions where accumulation mode aerosols have been scavenged (e.g., by low-level stratus clouds, which are common during the Arctic summer), evidence of rapid new particle production was observed. The seasonal cycle of atmospheric DMS closely resembles that of fine particles observed at Barrow, Alaska, and Alert, Northwest Territories, Canada. This finding indicates that DMS is likely an important precursor to the types of particles that dominate the background arctic aerosol in summertime. These results, together with those from several recently published studies of arctic aerosol, are combined to yield a consistent picture of the role of locally emitted DMS in the production of atmospheric aerosols in the Arctic in summer.

Optical properties of the aerosol from the 1991 Kuwait oil fires are calculated using measured aerosol size distributions and a spectral refractive index based on the measured chemical composition of the particulate matter. At a wavelength of 538 nm the calculated light-scattering coefficient agrees well with measurements, but the calculated single-scattering albedo is systematically higher by about 18% than the measured value. Radiative transfer calculations indicate maximum net daytime heating rates of 94 and 56 K d−1 for smoke 1 and 3 hours downwind of the fires, respectively. In the upper regions of the plume, where the calculated heating rates decrease with height, a radiauve-convective mixed layer developed. There was no significant temperature inversion at the top of this layer, which allowed rapid entrainment of air into the top of the plume, causing it to thicken at an observed rate of ∼0.1 m s−1. In addition, radiative heating of the plume as a whole caused it to lift as a unit at a measured rate of ∼0.1 m s−1 during the first few hours of plume evolution. A theory, based on mixed layer modeling and a scale analysis of the equations of motion, is presented that successfully reproduces the two rates of vertical transport. This model of the dynamics of a radiatively heated plume can be used to predict the evolution and lofting of large composite smoke plumes, such as those from forest fires; it also has implications for the transport, lifetime, and climatic importance of smoke generated on continental scales.

Ozone depletion occurred in the core of the plume of smoke from the Kuwait oil fires within 100 km of the fires, primarily in regions where NOx concentrations were high and ultraviolet flux was near zero. Rapid conversion of NO to NO2 can explain almost all of the ozone loss. Ozone was produced in diffuse regions of the plume, where the ultraviolet flux was higher than in the core. However, due to the relatively high ratio of nonmethane hydrocarbons to NOx, ozone production was slow. Since ozone was produced in a much larger volume than it was depleted, the plume as a whole was a source of ozone on a regional scale.

Airborne measurements in the smoke from the Kuwait oil fires in May and June 1991 indicate that the combined oil and gas emissions were equivalent to the consumption of about 4.6 million barrels of oil per day. The combustion was relatively efficient, with about 96% of the fuel carbon burned emitted as CO{sub 2}. Particulate smoke emissions averaged 2% of the fuel burned, of which about 20% was soot. About two-thirds of the mass of the smoke was accounted for by salt, soot, and sulfate. The salt most likely originated from oil field brines, which were ejected from the wells along with the oil. The salt accounts for the fact that many of the plumes were white. SO{sub 2} and NO{sub x} were removed from the smoke at rates of about 6 and 22% per hour, respectively. The high salt and sulfate contents explain why a large fraction of the particles in the smoke were efficient cloud condensation nuclei. 14 refs., 3 figs., 1 tab.

Total reactive nitrogen oxide (NO{sub y}) and NO were measured at the National Oceanic and Atmospheric Administration Geophysical Monitoring for Climate Change (NOAA GMCC) site at Barrow, Alaska, for 5 weeks during the spring of 1989. The data demonstrate the existance of a complex array of pollution sources which influence arctic air chemistry. During periods when 10-day back-trajectories indicated southerly flow, median NO{sub y} concentrations ranged from 284 to 467 ppt. When 10-day back-trajectories originated in the Arctic, median NO{sub y} concentrations ranged from 617 to 734 ppt., providing evidence for the long-range transport of pollutants to the Arctic known as arctic haze. The NO{sub y} concentrations observed during the spring background periods are significantly higher than previous measurements of NO{sub y} at Barrow taken during summer regardless of where the air mass originated. These observations provide evidence for a greatly increased NO{sub y} lifetime during the colder months over a large region of the background troposphere as well as the presence of much higher NO{sub y} concentrations in the Arctic. During four 12-60 hour events, substantially elevated NO{sub y} were observed in air not impacted by emissions from the town of Barrow. During these four events, peak NO{sub y}more » concentrations of 3 to 16 ppb were observed. Other data, including NO, SO{sub 2}, SO{sub 4}, and meteorology, were used to help identify the source region for the elevated NO{sub y} levels. These data present a consistent picture which indicates that during certain periods, elevated NO{sub y} levels are associated with air coming from the Prudhoe Bay industrial area approximately 300 km to the ESE and demonstrate that this facility is a major source of nitrogen oxides, and possibly other air pollutants, to the Alaskan Arctic.« less

Recent improvements to the carbonate-impregnated filter technique for measuring low-level SO2concentrations have resulted in dramatically improved performance. The improvements are (1) a better cleaning procedure for the paper filter substrates, resulting in approximately 60% reduction of their sulfate blank, (2) the use of an ion-exchange resin to remove the carbonate matrix from the sample extract, resulting in a 100% increase in the signal-to-noise ratio, (3) the use of high-purity glycerol in the filter impregnate, resulting in approximately 10% further reduction of blanks, and (4) improved Chromatographic and standardization procedures for more accurate quantification of sample peaks. Combined, these improvements allow measurements to be made of SO2 concentrations in marine background air with a 2σ uncertainty of ±6 parts per trillion by volume (pptv) and, based on this, a 3σ detection limit of 9 pptv for air volumes of 4 m3 (which can be collected in 15 min aboard our research aircraft). Measurements in polluted air show better than 95% collection efficiency, even at concentrations as high as 100 ppbv. Vertical profiles of SO2 measured during three research flights off the Washington coast (one in clean marine air) showed concentrations ranging from 15 to 86 pptv in the mixed layer and from 40 to 93 pptv in the free troposphere.