Study of the carbonaceous aerosol and morphological analysis of fine particles along with their mixing state in Delhi, India: a case study

Because of high emissions of anthropogenic as well as natural particles over the Indo-Gangetic Plains (IGP), it is important to study the characteristics of fine (PM₂.₅) and inhalable particles (PM₁₀), including their morphology, physical and chemical characteristics, etc., in Delhi during winter 2013. The mean mass concentrations of fine (PM₂.₅) and inhalable (PM₁₀) (continuous) was 117.6 ± 79.1 and 191.0 ± 127.6 μg m⁻³, respectively, whereas the coarse mode (PM₁₀–₂.₅) particle PM mass was 73.38 ± 28.5 μg m⁻³. During the same period, offline gravimetric monitoring of PM₂.₅ was conducted for morphological analysis, and its concentration was ~37 % higher compared to the continuous measurement. Carbonaceous PM such as organic carbon (OC) and elemental carbon (EC) were analyzed on the collected filters, and their mean concentration was respectively 33.8 and 4.0 μg m⁻³ during the daytime, while at night it was 41.2 and 10.1 μg m⁻³, respectively. The average OC/EC ratio was 8.97 and 3.96 during the day and night, respectively, indicating the formation of secondary organic aerosols during daytime. Effective carbon ratio was studied to see the effect of aerosols on climate, and its mean value was 0.52 and 1.79 during night and day, indicating the dominance of absorbing and scattering types of aerosols respectively into the atmosphere over the study region. Elemental analysis of individual particles indicates that Si is the most abundant element (~37–90 %), followed by O (oxide) and Al. Circularity and aspect ratio was studied, which indicates that particles are not perfectly spherical and not elongated in any direction. Trajectory analysis indicated that in the months of February and March, air masses appear to be transported from the Middle Eastern part along with neighboring countries and over Thar Desert region, while in January it was from the northeast direction which resulted in high concentrations of fine particles.