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. We present the first real-time composition of submicron particulate matter(PM1) in Old Delhi using high-resolution aerosol mass spectrometry(HR-AMS). Old Delhi is one of the most polluted locations in the world, andPM1 concentrations reached ∼ 750 µg m−3during the most polluted period, the post-monsoon period, where PM1 increasedby 188 % over the pre-monsoon period. Sulfate contributes the largestinorganic PM1 mass fraction during the pre-monsoon (24 %) and monsoon(24 %) periods, with nitrate contributing most during the post-monsoon period(8 %). The organics dominate the mass fraction (54 %–68 %) throughout thethree periods, and, using positive matrix factorisation (PMF) to performsource apportionment analysis of organic mass, two burning-related factorswere found to contribute the most (35 %) to the post-monsoon increase. Thefirst PMF factor, semi-volatility biomass burning organic aerosol (SVBBOA),shows a high correlation with Earth observation fire counts in surroundingstates, which links its origin to crop residue burning. The second is asolid fuel OA (SFOA) factor with links to local open burning due to its highcomposition of polyaromatic hydrocarbons (PAHs) and novel AMS-measured markerspecies for polychlorinated dibenzodioxins (PCDDs) and polychlorinateddibenzofurans (PCDFs). Two traffic factors were resolved: onehydrocarbon-like OA (HOA) factor and another nitrogen-rich HOA (NHOA)factor. The N compounds within NHOA were mainly nitrile species which havenot previously been identified within AMS measurements. Their PAHcomposition suggests that NHOA is linked to diesel and HOA to compressednatural gas and petrol. These factors combined make the largest relativecontribution to primary PM1 mass during the pre-monsoon and monsoonperiods while contributing the second highest in the post-monsoon period. Acooking OA (COA) factor shows strong links to the secondary factor,semi-volatility oxygenated OA (SVOOA). Correlations with co-located volatileorganic compound (VOC) measurements and AMS-measured organic nitrogen oxides(OrgNO) suggest SVOOA is formed from aged COA. It is also found that asignificant increase in chloride concentrations (522 %) from pre-monsoonto post-monsoon correlates well with SVBBOA and SFOA, suggesting that cropresidue burning and open waste burning are responsible. A reduction intraffic emissions would effectively reduce concentrations across most of theyear. In order to reduce the post-monsoon peak, sources such as funeralpyres, solid waste burning and crop residue burning should be consideredwhen developing new air quality policy.

atmospheric chemistry and physics

Seasonal analysis of submicron aerosol in Old Delhi using high-resolution aerosol mass spectrometry: chemical characterisation, source apportionment and new marker identification