CONCENTRATIONS OF CARBONYL-COMPOUNDS AND THE CARBON ISOTOPY OF FORMALDEHYDE AT A COASTAL SITE IN NOVA-SCOTIA DURING THE NARE SUMMER INTENSIVE

The concentrations of gaseous atmospheric carbonyl compounds have been measured at a coastal site on the southern tip of Nova Scotia during August 1993 as part of the National Oceanic and Atmospheric Administra tion's North Atlantic Regional Experiment (NARE) summer intensive. The DNPH-cartridge technique was used for sampling, with analysis by HPLC with UV absorbance detection. The carbon isotopic content of formalde hyde was measured using a novel collection technique on bisulfite-coat ed fillers followed by accelerator mass spectrometric determination of C-14 content and C-13/C-12 isotopic ratios. Results from this study i ndicate that quantifiable levels above about 100 parts per trillion by volume were found at the Chebogue Point, Nova Scotia, site for severa l carbonyls, formaldehyde, acetaldehyde, acetone, propionaldehyde, met hyl ethyl ketone, and benzaldehyde, for most 6-hour sampling periods. Six-hour averaged formaldehyde levels of <0.5 to about 3.5 parts per b illion were found during periods of local influence and during influen ce of continental air masses crossing eastern Canada and northeastern US. In contrast, background levels of formaldehyde of 200-400 pptv wer e found under conditions of predominantly marine back trajectories. La rge fractions of contemporary carbon (of the order of 80%) were found in collected formaldehyde samples for all transport regimes and formal dehyde concentrations, suggesting that biogenic sources of hydrocarbon precursors to formaldehyde predominated during the summer season.