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Sodium thiosulfate-coated ceramic denuders for ozone removal in ultrafine particle sampling
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DOI：10.5194/amt-19-4035-2026.png)
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Abstract
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Abstract. Ozone (O3) remaining in sampling air can artefactually alter the chemical composition of collected ultrafine particles (UFPs); biasing quantitative analysis of the chemical composition. In this study; we developed and evaluated a sodium-thiosulfate O3 denuder (TSOD) specifically tailored for UFP sampling and assessed its O3 scrubbing efficiency; particle losses; and chemical selectivity. In laboratory tests under controlled relative humidity and inlet O3 levels up to 200 ppbV; the outlet concentration remained consistently below the limit of detection; demonstrating the O3 removal efficiency of the TSOD. During an urban field deployment over 5 d O3 downstream of the TSOD consistently remained below the detection limit while ambient O3 varied between 0 and 65 ppbV. Moreover; for particles with mobility diameters ranging from 10 to 1000 nm; we did not observe any significant losses in particle number concentrations. Using a parallel two-channel UFP sampler (with vs. without upstream TSOD); we quantified O3-driven sampling artefacts in UFP mass focussing on three types of organic markers. (1) Firstly; we targeted polycyclic aromatic hydrocarbons (PAHs); particularly chrysene (Chry); benz[a]anthracene (BaA); benzo[a]pyrene (BaP); indeno[1; 2; 3-cd]pyrene (IcdP); benzo[k]fluoranthene (BkF); and benzo[b]fluoranthene (BbF). Without upstream O3 removal; the individual concentrations of the PAHs were 15 ± 3 %–46 ± 6 % lower. (2) Secondly; for the tire and road wear marker; the antioxidant N-(1; 3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and its oxidation product 6PPD-quinone (6PPDq); we observed in-situ ozonation of 6PPD to 6PPDq with transformation yields of about 13 ± 4 % to 20 ± 8 %. (3) In contrast; biogenic organic acids (bOAs) did not show differences when sampled with or without O3; as their O3 reactivity is much lower than the one of the PAHs. Moreover; this test indicated that the TSOD did not perturb the gas–particle partitioning of these semi-volatile species. Our results demonstrate that the TSOD (i) efficiently scrubs atmospheric O3 at relevant mixing ratios; (ii) does not introduce measurable particle losses across 10–1000 nm; and (iii) preserves semi-volatile partitioning.
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