Development of a Thermal Dissociation Chemiluminescence Instrument for In Situ Detection of HONO

We describe a new method for in situ detection of nitrous acid (HONO) using a combination of thermal dissociation (TD) and chemiluminescent (CL) detection of nitric oxide. A prototype was developed using a commercial NO sensor to evaluate the method. Laboratory tests for possible chemical interferences show that NO2, peroxy nitrates, alkyl nitrates, HNO3, O3 and H2O affect the measurements. A strategy for accounting for these effects is described. Our analyses show that HONO concentration observed using TD-CL will be accurate to ± 20% and that under typical urban conditions the method will have a detection limit of 5ppt.