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The Houston-Galveston Airshed (HGA) is one of the major metropolitan areas inthe US that is classified as a nonattainment area of federal ozone standards.Formaldehyde (HCHO) is a key species in understanding ozone relatedair pollution; some of the highest HCHO concentrations in North America havebeen reported for the HGA. We report on HCHO measurements in the HGA fromsummer 2006. Among several sites, maximum HCHO mixing ratios were observed inthe Houston Ship Channel (HSC), a region with a very high density ofindustrial/petrochemical operations. HCHO levels at the Moody Tower (MT) site close to downtown were dependent onthe wind direction: southerly maritime winds brought in background levels(0.5–1 ppbv) while trajectories originating in the HSC resulted in highHCHO (up to 31.5 ppbv). Based on the best multiparametric linear regressionmodel fit, the HCHO levels at the MT site can be accounted for as follows:38.5±12.3% from primary vehicular emissions (using CO as an index ofvehicular emission), 24.1±17.7% formed photochemically (usingperoxyacetic nitric anhydride (PAN) as an index of photochemical activity)and 8.9±11.2% from industrial emissions (using SO2 as an index ofindustrial emissions). The balance 28.5±12.7% constituted the residualwhich cannot be easily ascribed to the above categories and/or which istransported into the HGA. The CO related HCHO fraction is dominant during themorning rush hour (06:00–09:00 h, all times are given in CDT); on a carbonbasis, HCHO emissions are up to 0.7% of the CO emissions. The SO2 relatedHCHO fraction is significant between 09:00–12:00 h. After 12:00 h HCHO islargely formed through secondary processes. The HCHO/PAN ratios are dependenton the SO2 levels. The SO2 related HCHO fraction at the downtown siteoriginates in the ship channel. Aside from traffic-related primary HCHOemissions, HCHO of industrial origin serves as an appreciable source for OHin the morning

Formaldehyde and its relation to CO, PAN, and SO&lt;sub&gt;2&lt;/sub&gt; in the Houston-Galveston airshed

Formaldehyde and its relation to CO, PAN, and SO<sub>2</sub> in the Houston-Galveston airshed