Comment on egusphere-2023-700

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Fine particulate matter (PM_2.5) samples were collected between November 2020 and October 2021 at the Minzu University of China in Beijing and the <em>n</em>-alkyl nitrate concentrations in the PM_2.5 samples were determined to investigate <em>n</em>-alkyl nitrate pollution and formation mechanisms. C₉&ndash;C₁₆<em>n</em>-alkyl nitrate standards were synthesized and the <em>n</em>-alkyl nitrate concentrations in PM_2.5 were determined by gas chromatography triple quadrupole mass spectrometry. Temporal trends in and correlations between particulate-bound <em>n</em>-alkyl nitrate, ozone, PM_2.5, and nitrogen dioxide concentrations were investigated to assess the relationships between particulate-bound<em> n</em>-alkyl nitrate concentrations and photochemical reactions and identify the <em>n</em>-alkyl nitrate formation mechanisms. The <em>n</em>-alkyl nitrate concentrations in the PM_2.5 samples were 9.67&ndash;2730 pg/m³, and the mean was 578 pg/m³. The <em>n</em>-alkyl nitrate homologue group concentrations increased as the carbon chain length increased, i.e, long-chain <em>n</em>-alkyl nitrates contributed more than short-chain <em>n</em>-alkyl nitrates to the total <em>n</em>-alkyl nitrate concentrations in PM_2.5. The <em>n</em>-alkyl nitrate concentrations clearly varied seasonally and diurnally, the concentrations decreasing in the order winter &gt; spring &gt; autumn &gt; summer and the mean concentrations being higher at night than in the day. The particulate-bound <em>n</em>-alkyl nitrate and ozone concentrations significantly negatively correlated despite gas-phase alkyl nitrate and ozone concentrations previously being found to positively correlate. This indicated that long-chain alkyl nitrates may not be produced during photochemical reactions. The particulate-bound <em>n</em>-alkyl nitrate concentrations followed the same trends as and significantly positively correlated with the PM_2.5 and nitrogen dioxide concentrations. Nitrogen dioxide is an important contributor of nitrates in particulate matter. This indicated that particulate-bound <em>n</em>-alkyl nitrates may form through reactions between alkanes and nitrates on particulate matter surfaces. Particulate-bound <em>n</em>-alkyl nitrates are important components of PM_2.5 during haze events and strongly affect atmospheric visibility. Particulate-bound <em>n</em>-alkyl nitrates are secondary pollutants that strongly influence haze pollution.