AIRBORNE OBSERVATIONS RELATED TO OZONE DEPLETION AT POLAR SUNRISE

Airborne observations were conducted in the high Arctic (69 degrees N- 83 degrees N) during April 6-16, 1992, in support of the Polar Sunrise Experiment. Measurements of temperature, O-3, NOx, aerosol particles, inorganic aerosol species, inorganic bromide, alkyl nitrate species, and several organohalogens (including bromoform) were made from an alt itude of 30 m above ground level (agl) up to 7000 m msl (mean sea leve l). The average temperature profile shows a strong surface-based inver sion up to about 500 m, an isothermal region up to about 1.5 km, and s teadily decreasing from 1.5 to 6.8 km. Ozone mixing ratios were freque ntly found to be depleted from the surface up to various altitudes wit hin the boundary layer (maximum altitude for ozone <10 parts per billi on by volume (ppbv) was 375 m). The average ozone profile increases fr om <10 ppbv near the surface up to about 40 ppbv at 1 km, remaining ap proximately constant up to 5 km, and increasing with altitude thereaft er as the stratospheric source becomes evident. NOx, including a possi ble peroxyacetyl nitrate (PAN) interference, was typically <50 +/- 20 parts per trillion by volume (pptv), and frequently below detection li mit (20 pptv). Accumulation-mode aerosol particle number concentration s in the boundary layer were 100-200 cm(-3), and although CN increased low over a polynya, there were indications of an absence of nucleatio n-mode particles in ozone depleted air in the boundary layer compared with the free troposphere. Inorganic gaseous bromide, bromoform (CHBr3 ) and dibromochloromethane (CHClBr2) all exhibited strong anticorrelat ions with O-3. Gaseous nitrate (HNO3 plus possibly some contribution f rom PAN interference) ranged up to 110 ptv but was less than or equal to 40 pptv in 11 of 14 samples. With the exception of 1-propyl nitrate the C-3-C-6 alkyl nitrates correlated positively with ozone, as did t he isomer ratio C-3/C-6. Organohalogens were measured using charcoal c artridges {C} and Tenax cartridges {T}. CHBr3 was similar by both tech niques (medians of 1.83{C} and 1.60{T} pptv), and negative correlation s with O-3 were indicated by both sets of samples (R(2) = 0.75{C} and 0.71{T}). CHClBr2 was also very close in both sets of samples (median of 0.25{C} and 0.22{T} pptv), however, a negative correlation with O-3 was present only in the Tenax samples (R(2) = 0.63). Ln(CHClBr2/CHBr3 ) correlated negatively with ln(CHBr3) with a coefficient of determina tion of 0.75, and with higher ln(CHBr3) approached the value indicated by Li et al. (this issue) for air immediately above seawater at 0 deg rees C (i.e., 0.032). CHClBr2/CHBr3 was higher in the free troposphere than in the boundary layer and possibly less variant with ln(CHBr3), indicating either different source regions for these free troposphere organohalogens and/or, as Li et al. suggest, faster chemical destructi on of CHBr3 relative to CHClBr2 in the free troposphere. The airborne organohalogen data and that from ice camp SWAN (Hopper et al., this is sue) and Alert (Yokouchi et al., this issue) were combined to produce a vertical profile of CHBr3. CHBr3 exhibited a well-defined logarithmi c decrease with increasing altitude, indicating a strong surface sourc e, opposite to the average O-3 profile. In general, the low-level airb orne observations related to O-3 depletion are very consistent with th e observations at Alert, indicating that the many features of this phe nomenon are ubiquitous.