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. 2021 Jan 1:750:141461.
doi: 10.1016/j.scitotenv.2020.141461. Epub 2020 Aug 11.

Exceedances and trends of particulate matter (PM2.5) in five Indian megacities

Vikas Singh  1 , Shweta Singh  2 , Akash Biswal  2
Affiliations

Exceedances and trends of particulate matter (PM2.5) in five Indian megacities

Vikas Singh et al. Sci Total Environ. .

Abstract

Fine particulate matter (PM2.5) is the leading environmental risk factor that requires regular monitoring and analysis for effective air quality management. This work presents the variability, trend, and exceedance analysis of PM2.5 measured at US Embassy and Consulate in five Indian megacities (Chennai, Kolkata, Hyderabad, Mumbai, and New Delhi) for six years (2014-2019). Among all cities, Delhi is found to be the most polluted city followed by Kolkata, Mumbai, Hyderabad, and Chennai. The trend analysis for six years for five megacities suggests a statistically significant decreasing trend ranging from 1.5 to 4.19 μg/m3 (2%-8%) per year. Distinct diurnal, seasonal, and monthly variations are observed in the five cities due to the different site locations and local meteorology. All cities show the highest and lowest concentrations in the winter and monsoon months respectively except for Chennai which observed the lowest levels in April. All the cities consistently show morning peaks (~08: 00-10:00 h) and the lowest level in late afternoon hours (~15:00-16:00 h). We found that the PM2.5 levels in the cities exceed WHO standards and Indian NAAQS for 50% and 33% of days in a year except for Chennai. Delhi is found to have more than 200 days of exceedances in a year and experiences an average 15 number of episodes per year when the level exceeds the Indian NAAQS. The trends in the exceedance with a varying threshold (20-380 μg/m3) suggest that not only is the annual mean PM2.5 decreasing in Delhi but also the number of exceedances is decreasing. This decrease can be attributed to the recent policies and regulations implemented in Delhi and other cities for the abatement of air pollution. However, stricter compliance of the National Clean Air Program (NCAP) policies can further accelerate the reduction of the pollution levels.

Keywords: Air quality; Delhi; Emissions; Long-term trends; Pollution episodes; U.S. Embassy & Consulates.

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Conflict of interest statement

Declaration of competing interest The author(s) declare(s) that there is no conflict of interest regarding the publication of this article.

Figures

Unlabelled Image
Graphical abstract
Fig. 1
Fig. 1
Open street maps of the 2 km × 2 km area surrounding the embassy/consulates (red circle) to show the geographical location of the five Indian megacities (a. Chennai, b. Kolkata, c. Hyderabad, d. Mumbai, e. New Delhi). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 2
Fig. 2
Diurnal variation of PM2.5 in different seasons for (a) Chennai, (b) Kolkata, (c) Hyderabad, (d) Mumbai, (e) New Delhi, and (f) Annual diurnal variation across all cities. Scales are different.
Fig. 3
Fig. 3
Monthly variation of PM2.5 for (a) Chennai, (b) Kolkata, (c) Hyderabad, (d) Mumbai, (e) New Delhi, and (f) Annual monthly variation across all cities. Mean (black line) and median (color line) are shown as the line plot, whereas the shaded region shows 5th percentile and 95th percentile of the hourly concentrations across six years for the five cities.
Fig. 4
Fig. 4
STL decomposition and GLS regression of monthly mean PM2:5 for the five Indian megacities over a period of six years (2014–2019). The black line shows the STL trend component and the red line shows GLS fitted slope representing the overall trend in PM2.5. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 5
Fig. 5
Variability of PM2.5 episodes and their related statistics that exceeded the PM2.5 values corresponding to WHO standards (25 μg/m3) and Indian-NAAQS (60 μg/m3) during the 2014–2019 period for the five Indian megacities.
Fig. 6
Fig. 6
Exceedance in terms of the number of exceedances (magenta) and the trend in numbers of exceedances per year (blue) for varying threshold values for five Indian megacities. The shaded blues region shows 90% CI. Vertical red lines represent the WHO (dashed) and Indian NAAQS (dot-dashed) threshold limits. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 7
Fig. 7
Mean back-trajectories for the five megacities during four seasons for the period 2016–2019 classified into 5 trajectory clusters using HYSPLIT.
See this image and copyright information in PMC

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