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Abstract. We report on the development, characterization, and fielddeployment of a fast-time-response sensor for measuring ozone (O3) andnitrogen dioxide (NO2) concentrations utilizing chemical ionizationtime-of-flight mass spectrometry (CI-ToFMS) with oxygen anion(O2-) reagent ion chemistry. Wedemonstrate that the oxygen anion chemical ionization mass spectrometer(Ox-CIMS) is highly sensitive to both O3 (180 counts s−1 pptv−1) and NO2 (97 counts s−1 pptv−1), corresponding todetection limits (3σ, 1 s averages) of 13 and 9.9 pptv,respectively. In both cases, the detection threshold is limited by themagnitude and variability in the background determination. The short-termprecision (1 s averages) is better than 0.3 % at 10 ppbv O3 and 4 %at 10 pptv NO2. We demonstrate that the sensitivity of the O3measurement to fluctuations in ambient water vapor and carbon dioxide isnegligible for typical conditions encountered in the troposphere. Theapplication of the Ox-CIMS to the measurement of O3 vertical fluxesover the coastal ocean, via eddy covariance (EC), was tested during the summer of2018 at Scripps Pier, La Jolla, CA. The observed mean ozone depositionvelocity (vd(O3)) was 0.013 cm s−1 with a campaign ensemblelimit of detection (LOD) of 0.0027 cm s−1 at the 95 % confidencelevel, from each 27 min sampling period LOD. The campaign mean and 1standard deviation range of O3 mixing ratios was 41.2±10.1 ppbv. Several fast ozone titration events from local NO emissions weresampled where unit conversion of O3 to NO2 was observed,highlighting instrument utility as a total odd-oxygen (Ox=O3+NO2) sensor. The demonstrated precision, sensitivity, and timeresolution of this instrument highlight its potential for directmeasurements of O3 ocean–atmosphere and biosphere–atmosphere exchangefrom both stationary and mobile sampling platforms.
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Comparison of two photolytic calibration methods for nitrous acid
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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- Award ID(s):
- 2002928
- PAR ID:
- 10401523
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Atmospheric Measurement Techniques
- Volume:
- 15
- Issue:
- 18
- ISSN:
- 1867-8548
- Page Range / eLocation ID:
- 5455 to 5464
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/amt-15-5455-2022
