Meteorology and haze structure during AGASP-II, Part 1: Alaskan Arctic flights, 2?10 April 1986

Abstract

The second Arctic Gas and Aerosol Sampling Program (AGASP-II) was conducted across the Alaskan and Canadian Arctic in April 1986, to study the in situ aerosol, and the chemical and optical properties of Arctic haze. The NOAA WP-3D aircraft, with special instrumentation added, made six flights during AGASP-II. Measurements of wind, pressure, temperature, ozone, water vapor, condensation nuclei (CN) concentration, and aerosol scattering extinction (b~,) were used to determine the location of significant haze layers. The measurements rhade on the ftrst three flights, over the Arctic Ocean north of Barrow and over the Beaufort Sea north of Barter Island, Alaska are discussed in detail in this report of the first phase of AGASP II. In the Alaskan Arctic the WP-3D detected a large and persistent region of haze between 960 and 750 mb, in a thermally stable layer, on 2, 8, and 9 April 1986. At its most dense, the haze contained CN concentrations >10,000 cm -3 and bsp of 80 × 10 -6 m -1 suggesting active SO2 to H2SO4 gas-to-particle conversion. Calculations based upon observed SO2 concentrations and ambient relative humidities suggest that 104-105 small H2SO4 droplets 18 G.A. HERBERT ET AL.could have been produced in the haze layers. High concentrations of sub-micron H2SO 4 droplets were collected in haze. Ozone concentrations were 5-10 ppb higher in the haze layers than in the surrounding troposphere.Outside the regions of haze, CN concentrations ranged from 100 to 400 cm -3 and bsp values were about (20-40) × 10 -6 m-1. Air mass trajectories were computed to depict the air flow upwind of regions in which haze was observed. In two cases the back trajectories and ground measurements suggested the source to be in central Europe.

Meteorology and haze structure during AGASP-II, Part 2: Canadian Arctic flights, 13?16 April 1986

“…These layers of low aerosol concentrations may represent the condition of the polar air mass prior to a haze event. They may also represent a layer of air where aerosols have been preferentially removed through particle growth and cloud formation processes as mentioned earlier and discussed at length by Herbert et al 1989.…”

Analytical electron microscope studies of size-segregated particles collected during AGASP-II, flights 201?203

“…A possible explanation for the inverse relationship between CN counts and particle loading for these impactor samples is offered here. While the haze layers encountered during AGASP 201 contained large numbers of small particles (sometimes in excess of 60,000 cm -3) (Herbert et al, 1989), they actually contained relatively little aerosol mass. Thornton et al (1989) measured SO2 concentrations of up to 15 ppb in moist haze layers during AGASP 201.…”

“…Thornton et al (1989) measured SO2 concentrations of up to 15 ppb in moist haze layers during AGASP 201. Since unmixed transport of particles in concentrations such as these over several thousand km is unlikely, gas-to-particle conversion of SO2 into H2SO4 along the transport path could explain the high CN concentrations observed (Herbert et al, 1989). If the H2SO4 droplets were still being formed during sampling in the SO2-rich layers, the mean size of these particles would be quite small.…”

Surface aerosol measurements at Barrow during AGASP-II

“…The flight paths, and airborne CN and ¢rsp measurements were discussed by SchneU et al (1989). The large-scale meteorological situation during this time period was discussed by Herbert et al (1989).…”

“…It is clear that Arctic basin air was being sampled throughout the period of AGASP-II and that no rapid transport paths from populated middle-latitude areas to Barrow were active. However, Herbert et al (1989) show that such a transport path existed on 3 April to a location north of Barrow on the aircraft flight path.…”