Atmospheric formaldehyde sources in an urban winter environment

Formaldehyde is of interest to urban air chemistry because of its dual roles as an air toxic and a principal radical source involved in summertime ozone pollution. Formaldehyde and a number of other volatile organic compounds, (VOCs) trace gases (NOx, NOy, CO, O3) were measured in wintertime from Dec 2008 to January 2009 as part of the Treasure Valley PM2.5 campaign in Boise, Idaho. Formaldehyde and VOCs were measured by a proton transfer reaction mass spectrometer (PTR-MS). Mixing ratios of formaldehyde were as high as 9.5 ppbv during pollution events associated with stagnant conditions. Identifying sources of formaldehyde is typically difficult because of contributions from both primary emissions and secondary sources from biogenic and anthropoengic VOC oxidation. The wintertime study allowed us to assess the formaldehyde primary emissions in the absence of strong secondary production rates. The data were then analyzed by correlating formaldehyde mixing ratios to other measurements of gases and particle made during the study. Strong correlations between formaldehyde and other gases and particle number concentration were observed suggesting a strong contribution from vehicle emissions. Positive Matrix Factorization was also applied to the data to quantify source contribution factors. Comparison of the data to model output and emission inventories used by the regional AIRPACT-3 chemical forecast model will be presented.