Fast time response measurements of gaseous nitrous acid using a tunable diode laser absorption spectrometer: HONO emission source from vehicle exhausts

Abstract

We present the measurement of gaseous nitrous acid (HONO) using a tunable diode laser absorption spectrometer. This method utilizes one strong absorption feature at 1713.511cm−1, which is free of interference and suitable for ambient HONO measurements. The detection limit for a 1‐second integration time is determined to be better than 200 pptv. The measurement method has been demonstrated by sampling room air over an 11‐day period. HONO mixing ratios ranged from below the detection limit (≤200 pptv) to 4.8 ppbv, with a mean value of 0.73 ppbv. A number of elevated HONO events lasting from several seconds up to hours were observed and have been associated with roadway traffic adjacent to the building where the measurements were performed. The variation in the ratio of HONO/NOx and its anti‐correlation with ambient NOx measurements indicate that the source of HONO in this measurement study is mainly from the direct emission of traffic exhausts and local heterogeneous reactions. The demonstrated application of TDLAS fast response measurement technology is capable of providing new information on the sources and sinks of HONO in the environment.