Formaldehyde (CH 2 O) is a central component of photooxidation chemistry. The atmospheric sources of CH 2 O involve a complex mixture of biogenic and anthropogenic volatile organic compounds (VOCs). This study explores the geographical and altitudinal variations of CH 2 O production from its precursors over the Eastern U.S. and assesses the contributions from biogenic and anthropogenic VOC emissions to atmospheric CH 2 O.
Measurements of airborne CH 2 O and hydrocarbons over North America and model results were used to evaluate CH 2 O production from its precursors. Source attribution results from a photochemical box model indicate 95% of the CH 2 O arose in various proportions from a mixture of methane, isoprene, methyl hydroperoxide, methanol, and a peroxyacetyl group. Methane on average contributed 32% at altitudes below 2 km to CH 2 O production, 43% in 2-6 km, and 52% in 6-12 km. It was the predominant CH 2 O source in 1-12 km. Isoprene served as a major source of CH 2 O (range 0-72%, average 17%) over the southeastern U.S. region within 0-1-km layer. Methyl hydroperoxide was one of the predominant contributors over the ocean and averaged from 6 to 33% in all layers. Production from the peroxyacetyl group and methanol were 7-17% and 10-14% on average in the layers in 0-12 km, respectively.
A compound specific radiocarbon analysis technique was developed for atmospheric CH 2 O to examine its biogenic and anthropogenic carbon fraction. The method used filter collection, a preparative capillary gas chromatography isolation technique, and AMS detection. Ambient samples were collected on the roof of the CACS building at the Bay Campus of the University of RI, Narragansett, RI. The 14 CH 2 O data, 48-hour back trajectories, and VOC observations from the RI Department of Environmental Management were used to assess the relative contributions of biogenic and fossil precursors to CH 2 O. The results show a large fraction of fossil/industrial carbon in collected CH 2 O samples and imply the precursors of CH 2 O were dominated by fossil/industrial sources even during summer when biogenic sources are expected at their highest. It is suggested that pollutants from upwind coastal cities carried by the southwest sea breeze strongly influenced the site during our limited summer sample collection.
