Detection of aerosol organic nitrate and ammonium nitrate by Thermal Dissociation - Laser Induced Fluorescence

We demonstrate the ability to specifically detect both organic nitrates (R-ONO2) and ammonium nitrate in submicron particles. The technique is based on the well established method of Thermal Dissociation followed by Laser Induced Fluorescence of NO2 (TD-LIF) which has been previously used for detection of total (gas + particle) organic nitrates and nitric acid. In our application an activated carbon denuder is used at the inlet to remove the gas phase nitrates prior to detection yielding a particle only signal. The limit of detection is determined by the mixing ratio of NO2 produced by the thermal dissociation of RONO2 or HNO3, and for the instrument implemented here is 80 ppt NO2 for 10 seconds of signal averaging. This is equivalent to 0.20 µg/m3 of NO3- from ammonium nitrate at standard conditions. Results of chamber experiments are presented which demonstrate the unambiguous quantification of organic nitrates in the aerosol formed from oxidation of biogenic VOC.