Interference from HONO in the measurement of ambient air NO2 via photolytic conversion and quantification of NO  

作　　者：Nicholas J.Gingerysty Charles A.Odame-Ankrah Nick Jordan Hans D.Osthoff 

机构地区：[1]Department of Chemistry,University of Calgary,Calgary AB T2N 1N4,Canada [2]Global Analyzer Systems Ltd.,Calgary AB T2E 7L6,Canada

出　　处：《Journal of Environmental Sciences》2021年第9期184-193,共10页环境科学学报（英文版）

基　　金：by the Natural Sciences and Engineering Research Council of Canada (NSERC) through a Discovery grant (to H.D.O.);support by an Alberta Graduate Excellence Scholarship (AGES) award;Global Analyzer Systems for the loan of PhoNOTM photolytic converters。

摘　　要：The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide(NO_(2)) is NO-O_(3) chemiluminescence(CL), in which mixing ratios of nitric oxide(NO) are measured by sampling ambient air directly, and mixing ratios of NO_(x)(= sum of NO and NO_(2))are measured by converting NO_(2) to NO using, for example, heated molybdenum catalyst or,more selectively, photolytic conversion(P-CL).In this work, the nitrous acid(HONO) interference in the measurement of NO_(2) by P-CL was investigated.Results with two photolytic NO2 converters are presented.The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL.The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less.Mixing ratios of NO_(2),NO_(x) and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy(TD-CRDS).Both converters exhibited high NO_(2) conversion efficiency(CF_(NO2);> 90%) and partial conversion of HONO.Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s^(-1) and 2.9 s^(-1) for NO_(2) and 0.25 s^(-1) and 0.10 s^(-1) for HONO at 395 nm and 415 nm, respectively.CFHONOwas larger than predicted from the overlap of the emission and HONO absorption spectra.The results imply that measurements of NO2 by P-CL marginally but systematically overestimate true NO_(2) concentrations,and that this interference should be considered in environments with high HONO:NO_(2) ratios such as the marine boundary layer or in biomass burning plumes.

关 键 词：Photolytic conversion of NO_(2) HONO interference 

分 类 号：X831[环境科学与工程—环境工程]