Traffic related emissions of HONO and HCHO in Houston, TX

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, 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 a couple of weeks during late summer 2009. Primary purpose of this roadside study was to obtain HCHO/CO and HONO/CO ratios with a focus on time periods with limited photochemical processes, i.e. during nighttimes and rush-hour times. Photochemically active time periods vs time periods with limited photochemical processes were determined by concurrent PAN measurements. CO was used as a marker for traffic related emission processes and thus allowed to determine traffic related emissions of HCHO and HONO. Measurements of nitrogen oxides were used to gain insight into their relationship with HONO. The results of this study are compared to other existing data sets, which were mostly obtained in Europe and are thus based on a car fleet which is different from the US.