Nitrogen oxide measurements

Our group specializes on the quantifcation of nitrogen oxides in ambient abundance. We developed several innovative methods, such as blue diode laser thermal dissociation cavity ring-down spectroscopy (TD-CRDS) for quantification of NO2, total peroxyacyl nitrate (ΣPAN), and total alkyl nitrate (ΣAN) [Paul et al., 2009; Paul and Osthoff, 2010], red diode laser TD-CRDS for measurements of NO3 and N2O5 [Odame-Ankrah and Osthoff, 2011], iodide chemical ionization mass spectrometry (I--CIMS) for ClNO2 and PAN [Mielke et al., 2011; Thaler et al., 2011], and gas chromatography with electron capture detection (GC-ECD) for PAN [Rider et al., 2015; Tokarek et al., 2014]. Most recently, we built a cavity-enhanced absorption spectrometer (CEAS) to quantify HONO and NO2 [Jordan and Osthoff, 2020].

In TD-CRDS, mixing ratios of NO2 are quantified by absorption, and those of other nitrogen oxides are quantified (with uniform sensitivity) by difference following selective and quantitative conversion to NO2 in parallel channels. For example, we convert NO to NO2 by adding high O3 concentrations to the inlet, observing NOx concentrations, and then quantify NO by subtracting NO2 from the observed NOx signal. By heating the inlet, we can quantify HNO3, HONO, NO3-(p) and NO2-(p) [Garner et al., 2020]. The latter was applied to calibrate a scanning mobility particle sizer (SMPS), widely used to measure aerosol size distributions but for which few calibration methods exist. Our flagship blue diode TD-CRDS, called "Improved detection instrument for nitrogen oxide species" (iDinos), currently has 5 parallel detection channels.

Alas, our group has the expertise to quantify all major nitrogen oxides in ambient air, with exception of speciated AN. For an overview of our scientific instruments, please see this link.