Direct Measurements of Nitrous Acid, Nitrogen Dioxide and Formaldehyde in Auto Exhaust by Differential Optical Absorption Spectroscopy

摘要

To identify the sources of HONO which the authors have previously measured in ambient air in the California South Coast Air Basin (CSCAB), the authors have conducted continuous ambient air measurements of nitrous acid (HONO), formaldehyde (HCHO) and NO2 at a site adjacent to the I-10 freeway in Upland, CA, using the SAPRC long pathlength differential optical absorption spectrometer (DOAS) with about 0.5 km pathlength. HONO was observed during daylight hours for the first time in the CSCAB and well defined diurnal profiles were observed for HONO, NO2 and HCHO with concentrations up to 3 ppb, 150 ppb and 10 ppb, respectively. The data obtained defined the exposure to HONO of residents living adjacent to this heavily traveled freeway. In addition, a new open, multiple pass DOAS system was used to obtain direct measurements of HONO, HCHO, NO2, benzaldehyde, and SO2 in light duty motor vehicle (LDMV) exhaust. Eight vehicles were analyzed by placing this 'wall-less' DOAS system about 2 m behind the tailpipe. HONO is directly emitted in the exhaust of certain LDMV with markedly higher levels for older vehicles having limited emission control devices and exhibiting higher NOx emissions. Their results have implications for airshed modeling of photochemical air pollution and for health effects studies (since HONO is an inhalable nitrite), including investigations of the effects of dilute auto exhaust on experimental animals.