Sources and sinks of formaldehyde and acetaldehyde: An analysis of Denverʹs ambient concentration data

Four-hour average concentration data for formaldehyde and acetaldehyde have been collected in downtown Denver for each winter since December 1987, and on a year-round basis since October 1991. Carbon monoxide measurements have also been made at the same site since October 1991. These data have been analyzed in an attempt to identify the important sources and sinks for these carbonyl compounds in downtown Denver. We have found that motor vehicle emissions are a major source of these compounds all year. Although we do not find evidence for significant net photochemical production, we do find evidence for photochemical sources and sinks of both compounds. We have applied statistical techniques to ambient concentration data that can extract useful information about these atmospheric sources, sinks and processes, in spite of the large day-to-day variability in the data. Formaldehyde concentrations were found to have increased significantly during three recent winters when at least 2.6% oxygen-content fuel was required compared to two earlier winters when at least 2.0% oxygen-content fuel was required. The increase in formaldehyde concentration coincides with the increase in oxygenate content required in the fuel, but may be due to other causes