A history of C2-C4 NMHC and related compounds in the atmosphere from firn air cores in the Northern and Southern Hemispheres

Firn air samples were collected at sites in both the northern and southern polar regions for the analysis of a wide range of trace gases. Here we report on concentrations levels and recent trends in light non-methane hydrocarbons (C₂-C₄) and selected organic nitrate and halocarbon gases in these core samples. Sites in the Northern Hemisphere included Devon Island (Canada) and North Greenland (NGRIP). Southern Hemisphere sites included South Pole, Dome C, and Dronning Maud Land. Sites in the different hemispheres suggest increases in atmospheric NMHC up to the mid 1970's or early 1980's, followed by a slow decline. Alkyl nitrate distributions tended to follow the trends observed in parent hydrocarbons, with the exception of anomalous increases of methyl and ethyl nitrate with increasing depth in the northern hemisphere cores. The source of the anomalous alkyl nitrate increases (and some related halocarbon increases) has not been determined. Trends in NMHC will also be compared to trends in selected halocarbons (solvents, HCFCs, etc.) to evaluate similarities and differences in sources and emissions over the time periods of the twentieth century represented by the different firn air cores.