Urban-nonurban relationships of halocarbons, SF 6, N 2O, and other atmospheric trace constituents

Abstract

This paper presents the May 1976 northern hemispheric continental United States back-ground concentrations (ppt) of CC1 2F 2 (203.5), CC1 3F (115.6), CHC1 2F (14.2), CC1 2FCC1F 2 (19.9), SF 6 (0.24), CC1 4 (113.9), CHC1 3 (17.1), CH 3C1 (713.0), CH 3I (9.2), CH 3Br (4.7), CH 3CC1 3 (98.8), CC1 2CC1 2 (30.7), CHC1CC1 2 (15.6), COC1 2 (21.7), and N 2O (311.6 × 10 3). The data also indicate that the ambient burden of CC1 2F 2 and CC1 3F increased at an average rate of 1.6 ppt per month (11% per year) and 1.3 ppt per month (15% per year), respectively, during the first half of 1976. In addition, the urban-nonurban relationships of these and other pollutants (NO, NO 2, TNMHC, O 3, CH 4 and CO) have been discussed based on a total of six short-term field studies conducted in California at both urban and clean air locations. Significant concentration gradients of CHC1 3, CH 3C1, CH 3I and CH 3Br between marine and continental air masses suggest a marine source. In the case of CHC1 3 this gradient has been attributed to coastal water contamination. Seasonal variations of CH 3I and probably CH 3Br are found to exist in the marine environment. N 2O and CCI 4 are found to be relatively uniformly distributed with no significant temporal or spatial variation. From our data, the contribution of fluorinated species to the tropospheric chlorine budget (northern hemisphere) in 1976 is found to be about 33% which is comparable to a 28% natural chlorine contribution due solely to CH 3C1.