Abstract
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 + 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 aerosol-phase 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.
Highlights
Nitrogen-oxide-based functional groups are an area of significant interest in atmospheric oxidative chemistry
Organic nitrates are formed through reactions between volatile organic compounds (VOCs), of which the global majority are biogenic in origin (Seinfeld and Pankow, 2003; Perring et al, 2013) and NOx (=NO + NO2) or NO3 (Ng et al, 2017), which is predominantly anthropogenic in origin (Seinfeld and Pandis, 2006)
We included the IUPAC rate constant for a representative RO + O2 (7.2 × 10−14 e−1080/T, IUPAC), and OH wall loss rate from Knopf et al (2015). Based on these rate constants and the assumption that recombination or wall losses are the only fates for dissociated radicals, we found that the peroxy nitrates (PNs) measurement would be the most affected by recombination
Summary
Nitrogen-oxide-based functional groups are an area of significant interest in atmospheric oxidative chemistry. The two major organic-nitrate products of these reactions are alkyl nitrates (ANs) of the form RONO2 and peroxy nitrates (PNs) of the form ROONO2. Equilibrium partitioning of high molecular-weight, low-volatility organic molecules occurs, causing some organics to condense onto existing particles (Jimenez et al, 2009). These secondary organic aerosols (SOAs) consist primarily of the highly oxidized products of VOC + oxidant reactions because of their increased molecular weight and higher polarity. Keehan et al.: TD-CRDS instrument for measurement of organic nitrates ful for the detection of total peroxy and alkyl nitrates ( PNs and ANs, respectively) because they can be dissociated as a class, with identical detection efficiency regardless of the chemical nature of the R group. According to previous studies using charcoal denuders, the denuder removed the majority of particles with diameters < 0.1 μm (Glasius et al, 1999) as well as all semivolatile organic gases
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