LOWER TROPOSPHERIC MEASUREMENTS OF HALOGENS, NITRATES, AND SULFUR-OXIDES DURING POLAR SUNRISE EXPERIMENT 1992

During the international Polar Sunrise Experiment 1992 at Alert, Northwest Territories, Canada, in the high Arctic, atmospheric chemistry measurements were conducted from January to April to investigate lower tropospheric ozone depletion chemistry. A series of filter-based measurements involving a denuder and multistage filter holders were made to characterize the particulate and gaseous fraction of lower tropospheric SOx, Br, Cl, I, and NO3- relation to O-3 depletion events. Bromine compounds were the only ones of all those measured to show correlations with ozone depletion. All three components of total Br (particulate inorganic, gaseous inorganic, and gaseous organic) increased during O-3 depletion events. Temporal trends in halogens between the dark of January and the complete light of April were in some cases evident. Largely, as a result of more frequently occurring O-3 depletion-related episodes toward April, average concentrations of Br components tended to increase. The sum of inorganic particulate and gaseous Br increased from about 10 to 20 parts per trillion by volume (pptv) and organic gaseous Br increased from 25 to 40 pptv. Total inorganic I concentrations increased from about 0.3 pptv in early March to 1.0 pptv in late April. There was no systematic trend in total inorganic (gas plus particle) Cl with concentrations averaging approximately 40 pptv, while organic Cl trapped on charcoal was much more abundant. SOx concentrations averaged about 1200 pptv, decreasing from a maximum of 6000 pptv in January to 800 pptv in April and were well correlated with anthropogenic V. The fraction of SOx oxidized to SO4= increased progressively from a low of 20 to 30% in January to greater than 80% in April. SO4= concentrations increased from 500 pptv in January/February to 1000 pptv in March and dropped to 700 pptv in April. Inorganic NO3- showed no systematic variation throughout the period. It averaged 50 pptv, which is much less than peroxyacetyl nitrate (PAN) (150 to 600 pptv), and it was predominantly in particles. Judging from denuder observations, a filter combination of Teflon followed by two KOH filters can provide useful estimates of inorganic particulate Br- and NO3- as well as of inorganic gaseous Br-. Inorganic gaseous NO3- measurements from KOH and nylon filters suffer interferences from collection of PAN.