Emissions of radical precursors and related species from urban highway traffic

Nitrous acid (HONO) and formaldehyde (HCHO) are supposed to be important precursors for radicals and are believed to favor ozone formation significantly. So far only scarce traffic emissions data is available which includes both compounds. However, this knowledge is needed to further refine and validate air quality modeling. Here we will report measurements of HCHO, HONO, CO, CO2, NO/NO2/NOx, peroxyacyl nitrates (PAN), volatile organic compounds (VOCs) and meteorological parameters which were performed in the immediate vicinity of a highway junction in Houston for several months in 2009. Ratios of various trace gas species have been studied with respect to different environmental conditions (e.g. night vs day; low vs high relative humidity; low vs high ambient temperature) and traffic flow. The observational data will be compared to results of currently available mobile emissions models.