November 30th, 2023

Research News

The extended crop residue burning episodes in November 2023 & withdrawal of GRAP Stage IV – a bane or boon over Delhi air quality

The Aakash Project at RIHN is carrying out an intensive field campaign to measure PM2.5 and associated chemical species in northwest India in order to monitor the state of air pollution (https://aakash-rihn.org/en/data-set/). In our last three reports (RIHN news episode 1, 2 & 3, 2023), we introduced major pollution occurrences in northwest India as well as the government efforts in Delhi-NCR to reduce PM2.5 levels. This week continue to recorded low PM2.5 levels throughout the key CUPI-G (Compact and Useful PM2.5 Instrument with Gas sensor) sites (Figure 1) as compare to the first days of November. We  notice increasing PM2.5 levels at Faridkot and Sangrur on November 17 and 18, respectively, in conjunction with the rise in detection of fire counts. Maximum fire counts were recorded in the southwest region of Punjab from 15 - 17 November, when PM2.5 levels exceeded 150 µg m-3.

Figure 1: Time series of PM2.5 measured at the CUPI-G sites in Punjab, Haryana and Delhi NCR during 01 Oct to 22 Nov of 2022 and 2023. We also depict the rainfall around the sites in both years by green bars, and the green/red dots are marked on the final day of measurements. Data subjected to final quality control (QA/QC).
Figure 1: Time series of PM2.5 measured at the CUPI-G sites in Punjab, Haryana and Delhi NCR during 01 Oct to 22 Nov of 2022 and 2023. We also depict the rainfall around the sites in both years by green bars, and the green/red dots are marked on the final day of measurements. Data subjected to final quality control (QA/QC).

This year (2023) is witnessing a prolonged crop stubble burning period as compared to the previous years, while the cumulative fire count in 2023 is much lower than those in 2022 - about 25% and 50% lower for Punjab and Haryana, respectively, as of 20 Nov (AAKASH - Active Fire Report). Figure 2 suggests that the number of fire count detections in Punjab and Haryana have decreased steadily during 15-21 Nov. Additionally, the increase in wind speed and shift in wind direction altogether played a significant role in lowering PM2.5 levels during 19 Nov onwards. In general, we find a regional divide in the level of PM2.5 between the region of intense crop residue burning in Punjab and the Delhi NCR, which are separated by the rural areas of Haryana. The dense measurement network covering the rural regions and urban centres of the northwest India by the Aakash Project has helped us to hypothesize about this regional divide.

Figure 2: showing the progression of daily mean PM2.5 at CUPI-G sites (red dots), VIIRS fire counts and rainfall maps, and NCEP-FNL wind vectors at 10 m height. Plots available on regular basis at: https://aakash-rihn.org/en/data-set/
Figure 2: showing the progression of daily mean PM2.5 at CUPI-G sites (red dots), VIIRS fire counts and rainfall maps, and NCEP-FNL wind vectors at 10 m height. Plots available on regular basis at: https://aakash-rihn.org/en/data-set/

With the end of festive season in the third week of Nov, the Commission for Air Quality Management (CAQM) lifted the Graded Response Action Plan (GRAP) IV restrictions after its enforcement until 19 Nov (CAQM, 2023). GRAP IV had a significant impact on reduction of PM2.5 levels in Delhi-NCR during 5-8 Nov to about 250 µg m–3. The daily mean concentration of PM2.5 in the initial days of GRAP IV was > 250 µg m-3 which decreased to 150 µg m-3 on 19 Nov through reduction of primary PM2.5 emissions from constructions and road traffic etc. (Figure 3). However, during the 14 days of GRAP IV enforcement, 10 and 11 Nov were also impacted by the precipitation events, where the maximum decline in PM2.5 concentration (50–60 µg m–3) was observed. We now ask the question whether or not it’s too early to terminate GRAP IV and what would be its impact on Delhi air over the coming days, besides if there are visible impacts of crop residue burning events in northwest India.

Figure 3: PM2.5 & CO concentration over northwest regions (the NCR incorporates the region of Delhi, South-Haryana & Meerut (red)). The yellow dotted line is a marker for Diwali day. The shaded colour blocks represent the starts and terminations of the GRAP Stages.
Figure 3: PM2.5 & CO concentration over northwest regions (the NCR incorporates the region of Delhi, South-Haryana & Meerut (red)). The yellow dotted line is a marker for Diwali day. The shaded colour blocks represent the starts and terminations of the GRAP Stages.

Considering the reduction of PM2.5 level in Delhi-NCR, we further analyse the CUPI-G’s PM2.5 concentration for each site within it (Figure 4). During the high pollution events (2–5 Nov, https://www.chikyu.ac.jp/rihn_e/news/detail/410/) Sonipat (>550 µgm-3) recorded the maximum PM2.5 concentration followed by National Physical Laboratory (NPL) (>350 µg m-3) and the minimum was recorded at Delhi Technological University (DTU) at about 200 µg m-3. With the implementation of GRAP IV the levels of PM2.5 declined in almost all sites of Delhi-NCR. The change in wind direction (south-westerly, 270°) strongly influenced in lowering the PM2.5 levels (100 µg m-3) on 18-19 Nov even though the wind speed remained below 1 m s-1. Future analysis will elucidate the role of lifting GRAP IV on the PM2.5 levels.

Figure
Figure 4: Similar to Figure 3 but for PM2.5 at the different sites in the Delhi-NCR. In addition, wind speed and wind direction (in degree; 90o is from north or northerly).

References

RIHN Research news, episode 1, Very high air pollution event on 2-5 Nov 2023 in Delhi NCR couldn’t be explained by crop residue burning. 08 November 2023; www.chikyu.ac.jp/rihn_e/news/detail/410/

RIHN Research news, episode 2, Government policy to decrease major emission sources led to reduction in PM2.5 in the Delhi NCR during 4-9 November 2023. 14 November 2023; https://www.chikyu.ac.jp/rihn_e/news/detail/414/

RIHN Research news, episode 3, The northwest India gets a respite from high PM2.5 due to rainfall on 10th Nov 2023 but the regional PM2.5 behaviour changed within 2 days. 22 November 2023; https://www.chikyu.ac.jp/rihn_e/news/detail/415/

Commission for Air Quality Management (CAQM). Revocation of Actions under Stage-IV (‘Severe+’ Air Quality) of revised Graded Response Action Plan in Delhi-NCR. 18 Nov 2023; https://caqm.nic.in/index1.aspx?lsid=4168&lev=2&lid=4171&langid=1.

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