First real-time source apportioned study quantifies elemental loads in Delhi’s winter pollution

In a first-of-its-kind assessment for Delhi, scientists from IIT-K conducted real-time analyses of ambient air during the two consecutive winters of 2018 and 2019, revealing key sources of polluting elements (metals and non-metals) in PM 10 and PM 2.5. The study calculated the elemental composition of particulate matter and took into account wind direction, to calculate the pollution load at a point. It showed that each element carried fingerprints from a particular industry. 

The dominant PM10 elements were chlorine, sulphur and crustal material (ie, silicon, calcium, titanium, and iron). The elements measured amounted to around 25% of total PM10 in 2018 and around 19% in 2019. To investigate the composition of ambient air, scientists installed a suite of semi-continuous online and online aerosol instruments at the Indian Institute of Technology Delhi (IITD) campus in South Delhi. Punjab and Haryana in the northwest and Uttar Pradesh to the east of Delhi were the most influential source regions for various pollutants, the study stated.

According to the study, the source of chlorine-bromine-selenium (Cl-Br-Se) were likely influenced by sources from Punjab and Haryana as well as local sources within Delhi. Dust, non-exhaust and Solid Fuel Combustion (SFC1) had local origin. Sulphur-rich air and chromium-nickel-manganese (Cr-Ni-Mn) likely originated in Uttar Pradesh (northeast to southeast), the copper-cadmium-lead (Cu-Cd-Pb) from Nepal and Uttar Pradesh (east), while lead-tin-selenium (Pb-Sn-Se) and Solid Fuel Combustion (SFC2) originated in Haryana, Punjab and Pakistan (northwest), the research said. While establishing the northwest and the east as two major corridors for pollutants entering the national capital, the study points specifically at industrial units and thermal power plants for chlorine and sulphur loads in Delhi’s air.

Dust and non-exhaust sources strongly contributed to elemental PM10, while the remaining sources and elements were mostly associated with elemental PM2.5. The study revealed that the concentrations for the chlorine-bromine-selenium (Cl-Br-Se) and lead-tin-selenium (Pb-Sn-Se) decreased with increasing temperature and wind speed and decreasing humidity.

Data for the study was collected every 30 minutes for both PM2.5 and PM10 during the winters of 2018 and 2019 by a team of 15 researchers from the Indian Institute of Technology (IIT)-Kanpur; IIT-Delhi; Laboratory of Atmospheric Chemistry (LAC), Switzerland; Physical Research Laboratory; Ahmedabad; and Laboratoire des Sciences du Climat et de l’environnement, France.

 Hourly data on temperature, wind speed, wind direction, visibility and relative humidity were obtained from the Indira Gandhi International Airport. The mean of total PM10 mass during the campaigns was ~271 μg m-3 in 2018 (20 January–11 March) and ~300 μg m-3 in 2019 (15 January–9 February), whereas the mean of total PM2.5 mass was ~180 μg m-3 during the 2019 campaign. The study said since particle size determines the rate and depth of penetration into the respiratory tract, mitigating health impacts depended on data resolved by particle size. For example, research revealed that reacted chlorine (Cl) was found in PM1.0-0.3, whereas sea/road salt related chlorine resided in PM10-2.5. Similarly, potassium in PM1.0 mostly originates from wood burning, but is attributed to dust in PM10–1.0. The study concluded that to facilitate PM mitigation strategies, pollution sources need to be identified and apportioned.