Abstract. Nitrous acid (HONO) plays an important role in troposphericoxidation chemistry as it is a precursor to the hydroxyl radical (OH).Measurements of HONO have been difficult historically due to instrumentinterferences and difficulties in sampling and calibration. The traditionalcalibration method involves generation of HONO by reacting hydrogen chloridevapor with sodium nitrite followed by quantification by various methods(e.g., conversion of HONO to nitric oxide (NO) followed by chemiluminescencedetection). Alternatively, HONO can be generated photolytically in thegas phase by reacting NO with OH radicals generated by H2O photolysis.In this work, we describe and compare two photolytic HONO calibrationmethods that were used to calibrate an iodide adduct chemical ionizationmass spectrometer (CIMS). Both methods are based on the water vaporphotolysis method commonly used for OH and HO2 (known collectively asHOx) calibrations. The first method is an adaptation of the common chemicalactinometry HOx calibration method, in which HONO is calculated based onquantified values for [O3], [H2O], and [O2] and the absorptioncross sections for H2O and O2 at 184.9 nm. In the second, novelmethod HONO is prepared in mostly N2 ([O2]=0.040 %) and issimply quantified by measuring the NO2 formed by the reaction of NOwith HO2 generated by H2O photolysis. Both calibration methodswere used to prepare a wide range of HONO mixing ratios between∼400 and 8000 pptv. The uncertainty of the chemicalactinometric calibration is 27 % (2σ) and independent of HONOconcentration. The uncertainty of the NO2 proxy calibration isconcentration-dependent, limited by the uncertainty of the NO2measurements. The NO2 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 associatedwith a mixing ratio of ∼1600 pptv, typical of valuesobserved in urban areas at night. We also describe the potential applicationof the NO2 proxy method to calibrating HOx instruments (e.g., LIF,CIMS) at uncertainties below 15 % (2σ).
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An investigation into the chemistry of HONO in the marine boundary layer at Tudor Hill Marine Atmospheric Observatory in Bermuda
Abstract. Here we present measurement results of temporal distributions of nitrous acid (HONO) along with several chemical and meteorologicalparameters during the spring and the late summer of 2019 at Tudor Hill Marine Atmospheric Observatory in Bermuda. Large temporal variations inHONO concentration were controlled by several factors including local pollutant emissions, air mass interaction with the island, andlong-range atmospheric transport of HONO precursors. In polluted plumes emitted from local traffic, power plant, and cruise ship emissions,HONO and nitrogen oxides (NOx) existed at substantial levels (up to 278 pptv and 48 ppbv, respectively),and NOx-related reactions played dominant roles in daytime formation of HONO. The lowest concentration of HONO wasobserved in marine air, with median concentrations at ∼ 3 pptv around solar noon and < 1 pptv during thenighttime. Considerably higher levels of HONO were observed during the day in the low-NOx island-influenced air([NO2] < 1 ppbv), with a median HONO concentration of ∼ 17 pptv. HONO mixing ratios exhibiteddistinct diurnal cycles that peaked around solar noon and were lowest before sunrise, indicating the importance of photochemical processes forHONO formation. In clean marine air, NOx-related reactions contribute to ∼ 21 % of the daytime HONOsource, and the photolysis of particulate nitrate (pNO3) can account for the missing source assuming a moderate enhancement factorof 29 relative to gaseous nitric acid photolysis. In low-NOx island-influenced air, the contribution from bothNOx-related reactions and pNO3 photolysis accounts for only ∼ 48 % of the daytime HONOproduction, and the photochemical processes on surfaces of the island, such as the photolysis of nitric acid on the forest canopy, might contributesignificantly to the daytime HONO production. The concentrations of HONO, NOx, and pNO3 were lowerwhen the site was dominated by the aged marine air in the summer and were higher when the site was dominated by North American air in the spring,reflecting the effects of long-range transport on the reactive nitrogen chemistry in background marine environments.
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- PAR ID:
- 10351475
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 22
- Issue:
- 9
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 6327 to 6346
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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