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- Title
Comparison of two photolytic calibration methods for nitrous acid.
- Authors
Lindsay, Andrew J.; Wood, Ezra C.
- Abstract
Nitrous acid (HONO) plays an important role in tropospheric oxidation chemistry as it is a precursor to the hydroxyl radical (OH). Measurements of HONO have been difficult historically due to instrument interferences and difficulties in sampling and calibration. The traditional calibration method involves generation of HONO by reacting hydrogen chloride vapor with sodium nitrite followed by quantification by various methods (e.g., conversion of HONO to nitric oxide (NO) followed by chemiluminescence detection). Alternatively, HONO can be generated photolytically in the gas phase by reacting NO with OH radicals generated by H 2 O photolysis. In this work, we describe and compare two photolytic HONO calibration methods that were used to calibrate an iodide adduct chemical ionization mass spectrometer (CIMS). Both methods are based on the water vapor photolysis method commonly used for OH and HO 2 (known collectively as HO x) calibrations. The first method is an adaptation of the common chemical actinometry HO x calibration method, in which HONO is calculated based on quantified values for [O 3 ], [H 2 O], and [O 2 ] and the absorption cross sections for H 2 O and O 2 at 184.9 nm. In the second, novel method HONO is prepared in mostly N 2 ([O 2]=0.040 %) and is simply quantified by measuring the NO 2 formed by the reaction of NO with HO 2 generated by H 2 O photolysis. Both calibration methods were used to prepare a wide range of HONO mixing ratios between ∼400 and 8000 pptv. The uncertainty of the chemical actinometric calibration is 27 % (2σ) and independent of HONO concentration. The uncertainty of the NO 2 proxy calibration is concentration-dependent, limited by the uncertainty of the NO 2 measurements. The NO 2 proxy calibration uncertainties (2σ) presented here range from 4.5 % to 24.4 % (at [HONO] =8000 pptv and [HONO] =630 pptv, respectively) with a 10 % uncertainty associated with a mixing ratio of ∼1600 pptv, typical of values observed in urban areas at night. We also describe the potential application of the NO 2 proxy method to calibrating HO x instruments (e.g., LIF, CIMS) at uncertainties below 15 % (2σ).
- Subjects
NITROUS acid; ABSORPTION cross sections; CALIBRATION; HYDROGEN chloride; TROPOSPHERIC chemistry; HYDROXYL group; TROPOSPHERIC aerosols
- Publication
Atmospheric Measurement Techniques, 2022, Vol 15, Issue 18, p5455
- ISSN
1867-1381
- Publication type
Article
- DOI
10.5194/amt-15-5455-2022