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

Abstract

Abstract. 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, and PM1 concentrations reached ∼ 750 µg m−3 during the most polluted period, the post-monsoon period, where PM1 increased by 188 % over the pre-monsoon period. Sulfate contributes the largest inorganic 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 the three periods, and, using positive matrix factorisation (PMF) to perform source apportionment analysis of organic mass, two burning-related factors were found to contribute the most (35 %) to the post-monsoon increase. The first PMF factor, semi-volatility biomass burning organic aerosol (SVBBOA), shows a high correlation with Earth observation fire counts in surrounding states, which links its origin to crop residue burning. The second is a solid fuel OA (SFOA) factor with links to local open burning due to its high composition of polyaromatic hydrocarbons (PAHs) and novel AMS-measured marker species for polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Two traffic factors were resolved: one hydrocarbon-like OA (HOA) factor and another nitrogen-rich HOA (NHOA) factor. The N compounds within NHOA were mainly nitrile species which have not previously been identified within AMS measurements. Their PAH composition suggests that NHOA is linked to diesel and HOA to compressed natural gas and petrol. These factors combined make the largest relative contribution to primary PM1 mass during the pre-monsoon and monsoon periods while contributing the second highest in the post-monsoon period. A cooking OA (COA) factor shows strong links to the secondary factor, semi-volatility oxygenated OA (SVOOA). Correlations with co-located volatile organic compound (VOC) measurements and AMS-measured organic nitrogen oxides (OrgNO) suggest SVOOA is formed from aged COA. It is also found that a significant increase in chloride concentrations (522 %) from pre-monsoon to post-monsoon correlates well with SVBBOA and SFOA, suggesting that crop residue burning and open waste burning are responsible. A reduction in traffic emissions would effectively reduce concentrations across most of the year. In order to reduce the post-monsoon peak, sources such as funeral pyres, solid waste burning and crop residue burning should be considered when developing new air quality policy.

Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes

“…The absence of nighttime oxidation chemistry is further corroborated by a study by Cash et al, which reported a reduction in oxidized aerosol levels in Delhi during the postmonsoon period at night, alongside increased levels of hydrocarbon-like organic aerosol (HOA). 41 Together, these model and measurement observations provide strong evidence for a deviation from the typical nocturnal oxidation chemistry observed in other highly polluted urban atmospheres. More details about the observed VOC concentrations and diel profiles can be found in refs 19 and 42.…”

Chemical Composition and Source Apportionment of Total Suspended Particulate in the Central Himalayan Region

“…Cl − also received a significant contribution from the biomass burning source (~32%), although its mass concentration was generally low. Several studies in India have verified the affinity of chloride with biomass burning sources [92,93]. The high OC/EC ratio of 6.9 in the source profile is indicative of processed BB emissions.…”

Biogenic and anthropogenic sources of isoprene and monoterpenes and their secondary organic aerosol in Delhi, India

“…SO 2 was measured using a 43i SO 2 analyser (Thermo Scientific). High-resolution aerosol mass spectrometry measurements were conducted as outlined in Cash et al (2021). Ion chromatography measurements were undertaken by the experimental approach outlined by as part of an intercomparison study.…”

“…The complex sources of isoprene and monoterpenes in highly polluted urban areas make source identification difficult. As such, the secondary organic aerosol (SOA) markers in this study are referred to as originating from isoprene or monoterpenes, but the emissions are likely from a mixture of biogenic and anthropogenic sources as discussed previously (Cash et al, 2021;Nelson et al, 2021).…”