VARIABILITY OF SO4=, TOTAL SULFATE, NO3-, AND TOTAL NITRATE SCAVENGING RATIOS FOR THE FRONTAL BOUNDARY STUDY

Precipitation and air concentration data collected during a U.S. Depar tment of Energy-sponsored Frontal Boundary Study (FBS) were used to ca lculate scavenging ratios. The precipitation data were collected on a 100 km x 100 km surface grid containing 36 sampling sites, while the a ir concentration data were collected by aircraft. Radar and rawinsonde data were used to position the aircraft into the air moss feeding the precipitation. The coordination of the aircraft data with surface pre cipitation data allows the calculation of scavenging ratios. During th e study, three out of seven events sampled allowed the calculation of scavenging ratios for SO4=, total sulfate, NO3-, and total nitrate. Th e 36 precipitation samplers allowed calculation of multiple scavenging ratios to represent an event. From these scavenging ratios, both a ge ometric mean and a geometric standard deviation of the scavenging rati o were calculated for each event. The geometric mean (geometric standa rd deviation) scavenging ratio for total sulfate is 6 x 10(4) (1.1) fo r 10 October 1989, 10 x 10(4) (1.5) for 16-17 October 1989, and 4 x 10 (4) (1.3) for 31 October 1989. For SO4= the scavenging ratios are 10 x 10(5) (1.1) for 10 October 1989, 4 x 10(5) (1.5) for 16-17 October 19 89, and 3 x 10(5) (1.3) for 31 October 1989. The scavenging ratio for NO2- is 3 x 10(6) (1.2) for 10 October 1989, 10 x 10(6) (1.4) for 16-1 7 October 1989, and 0.4 x 10(6) (1.5) for 31 October 1989. The scaveng ing ratio for total nitrate is 2 x 10(6) (1.2) for 10 October 1989, 2 x 10(6) (1.4) For 16-17 October 1989, and 0.2 x 10(6) (1.5) for 31 Oct ober 1989. The most important finding is the small variation of the nu mbers within the events as reflected in the geometric standard deviati ons. These values ranged from 1.1 to 1.5. Based on these results, a si ngle scavenging ratio can be used on a 100 km x 100 km area with a min imum of error. Two other results were found when comparing these scave nging ratios to total precipitation in the sampler. The comparison rev ealed that the variation in the scavenging ratio increased with decrea sing total precipitation. The increase was up to a factor of 2 for les s than 5 mm when compared with greater than 5 mm of total precipitatio n.