INTERNAL CONSISTENCY TESTS FOR EVALUATION OF MEASUREMENTS OF ANTHROPOGENIC HYDROCARBONS IN THE TROPOSPHERE

Measurements of tropospheric nonmethane hydrocarbons (NMHCs) made in c ontinental North America should exhibit a common pattern determined by photochemical removal and dilution acting upon the typical North Amer ican urban emissions. We analyze I I data sets collected in the United States in the context of this hypothesis, in most cases by analyzing the geometric mean and standard deviations of ratios of selected NMHCs . in the analysis we attribute deviations from the common pattern to p lausible systematic and random experimental errors, in some cases the errors have been independently verified and the specific causes identi fied. Thus this common pattern provides a check for internal consisten cy in NMHC data sets. Specific tests are presented which should provid e useful diagnostics for all data sets of anthropogenic NMHC measureme nts collected in the United States. Similar tests, based upon the perh aps different emission patterns of other regions, presumably could be developed. The specific tests include(1) a lower limit for ethane conc entrations, (2) specific NMHCs that should be detected if any are, (3) the relatively constant mean ratios of the longer-lived NMHCs with si milar atmospheric lifetimes, (4) the constant relative patterns of fam ilies of NMHCs, and (5) limits on the ambient variability of the NMHC ratios. Many experimental problems are identified in the literature an d the Southern Oxidant Study data sets. The most important conclusion of this paper is that a rigorous field intercomparison of simultaneous measurement ambient NMHCs by different techniques and researchers is of crucial importance to the field of atmospheric chemistry. The tests presented here are suggestive of errors but are not definitive; only a field intercomparison can resolve the uncertainties.