Real Time In Situ Detection of Organic Nitrates in Atmospheric Aerosols

A novel instrument is described that quantifies total particle-phase organic nitrates in real time with a detection limit of 0.11 μg m⁻³ min⁻¹, 45 ppt min⁻¹ (−ONO₂). Aerosol nitrates are separated from gas-phase nitrates with a short residence time activated carbon denuder. Detection of organic molecules containing −ONO₂ subunits is accomplished using thermal dissociation coupled to laser induced fluorescence detection of NO₂. This instrument is capable of high time resolution (seconds) measurements of particle-phase organic nitrates, without interference from inorganic nitrate. Here we use it to quantify organic nitrates in secondary organic aerosol generated from high-NO_<i>x</i> photooxidation of limonene, α-pinene, Δ-3-carene, and tridecane. In these experiments the organic nitrate moiety is observed to be 6−15% of the total SOA mass.