Abstract:
Urban areas in developing countries are major sources of carbonaceous aerosols and air pollutants, pointing out the need for a
detailed assessment of their levels and origin close to the source. A multi-instrument research campaign was performed in Delhi
during December 2015–February 2016 aimed at exploring the pollution levels and the contribution of various sources to
particulate matter (PM) concentrations, black carbon (BC) aerosols, and trace gases. The weak winds (< 5–6ms−1
) along with
the shallow boundary layer favoured the formation of thick and persistent fog conditions, which along with the high BC (24.4 ±
12.2 μg m−3
) concentrations lead to the formation of smog. Very high pollution levels were recorded during the campaign, with
mean PM10, PM2.5, CO, NO, and O3 concentrations of 245.5 ± 109.8 μg m−3
, 145.5 ± 69.5 μg m−3
, 1.7 ± 0.5 ppm, 7.9 ± 2.3 ppb,
and 31.3 ± 18.4 ppb, respectively. This study focuses on examining the daily/diurnal cycles of the aerosol optical properties
(extinction, scattering, absorption coefficients, single scattering albedo), as well as of PM and other pollutant concentrations,
along with changes in meteorology (mixing-layer height and wind speed). In addition, the hot-spot pollution sources in the
greater Delhi area were determined via bivariate plots and conditional bivariate probability function (CBPF), while the distant
sources were examined via the concentration weighted trajectory (CWT) analysis. The results show that the highest aerosol
absorption and scattering coefficients, PM, and trace gas concentrations are detected for weak winds (< 2 m s−1
) with a preference
for eastern directions, revealing high contribution from local sources and accumulation of pollutants within urban Delhi.
