Measurement of high concentration of nitrous acid inside automobiles

Nitrous acid concentration levels have been measured inside motor vehicles by using the annular denuder technique. The results indicate that quite high levels of nitrous acid (10–25 ppb) occur inside the autos during transit through polluted areas (urban sites) and that high concentrations persist for many hours even in the cast: where the autos are moved to an unpolluted site. HONO/NO2 ratio has been also measured and found to be much higher inside than outside the autos. The influence of indoor temperature on HONO concentration has been studied and found to be very significant. All these findings confirm the heterogeneous nature of HONO formation reaction and the major role played by the adsorption-desorption mechanism in determining the indoor concentration of this pollutant, whose effects on human health still need to be thoroughly evaluated.