A thermal-dissociation-cavity ring-down spectrometer (TD-CRDS) for the detection of organic nitrates in gas and particle phases

Abstract

A thermal-dissociation-cavity ring-down spectrometer (TD-CRDS) was developed to measure NO2, peroxy nitrates (PNs), alkyl nitrates (ANs), and HNO3 in the gas and particle phase, built using a commercial Los Gatos Research NO2 analyzer. The detection limit of the TD-CRDS is 0.66 ppb for ANs, PNs, and HNO3 and 0.48 ppb for NO2. For all four classes of NOy , the time resolution for separate gas and particle measurements is 8 min, and for total gas C particle measurements it is 3 min. The accuracy of the TD-CRDS was tested by comparison of NO2 measurements with a chemiluminescent NOx monitor and aerosolphase ANs with an aerosol mass spectrometer (AMS). N2O5 causes significant interference in the PN and AN channel under high oxidant concentration chamber conditions, and ozone pyrolysis causes a negative interference in the HNO3 channel. Both interferences can be quantified and corrected for but must be considered when using TD techniques for measurements of organic nitrates. This instrument has been successfully deployed for chamber measurements at widely varying concentrations, as well as ambient measurements of NOy.