Current World Environment

The Short-Lived Climate Pollutants (SLCPs) such as black carbon (BC), tropospheric ozone, methane and hydrofluorocarbons (HFCs) play very important role in climate change.¹¹ Due to their relatively  shorter lifetime in the atmosphere, these are termed as Short-Lived Pollutants. For example black carbon and tropospheric ozone have lifetime of few weeks; methane and HFCs last around two decades. SLCPs adversely impact air quality and can accelerate global warming, sea level rise and other climate change related phenomenon.  

Black carbon, also known as soot, is emitted from incomplete combustion of fossil fuels, biomass and biofuels. It causes dimming and contributes to positive radiative forcing.¹⁰ The BC forms a significant fraction of PM_2.5 and PM₁₀ aerosols having human health effects too. Every year 7 million deaths occur due to air pollution (https://www.ccacoalition.org/en/slcps/black-carbon). Major sources of ozone precursors in the urban areas include automobile and industrial emissions whereas methane is mainly emitted by paddy fields, livestock production, sewage and wetlands. Methane is a greenhouse gas having global warming potential 25 times higher than the carbon dioxide. HFCs are used in air conditioning and refrigeration etc. Their global warming potential is several times greater than other greenhouse gases. 

South Asian region is among one of the most densely populated regions around the world. The region is vulnerable to the impacts of black carbon.^{6, 13} The BC levels in the region pose a major challenge for tackling climate change. Extensive use of various fuels such as biomass, woods, cow dung cake for domestic cooking and tyre burning and other waste burning for wintertime heating purposes along with adulterated fuels and unchecked vehicular pollution emit huge quantities of BC or soot which degrades the air quality and result in hazy atmosphere, further having significant climate change and human health impacts.^{8, 12} The BC also interacts with atmospheric dust forming carbon-dust composites which are deposited on the surfaces and foliage affecting plants, buildings and waterbodies  BC levels have been reported eight times higher in urban atmospheric dust as compared to its corresponding soil⁹ .Soft approaches involving mindset change can help in reducing BC emissions.¹⁴

Furthermore, the tropospheric ozone is a greenhouse gas and contributes to climate change. Generally, it is formed by the reaction of volatile hydrocarbons and nitrogen oxides. Tropospheric ozone is also considered as phytotoxic and affects grassland and tree species^{1, 4, 5}  Recently, ozone levels have been reported higher during COVID 19 pandemic.³ However, during pre-pandemic period (summers of 2019) also, ozone levels were reported higher at the industrial sites in NCR Delhi. This has been explained due to action taken by the Environmental Pollution Control Authority (EPCA) through an implementation of  the total ban on plastic burning and closure of illegal tire oil units in Delhi⁷. This led to reduction in emissions of chlorine and hydrochloric acid which in turn helped in reduced levels of ozone. However, this needs comprehensive investigation across south Asia as the plastic burning activities are common in the region.

Therefore, monitoring based mitigation solutions of SLCPs are required worldwide as well as on regional scale. Promotion of best practices and showcasing the successful global and regional level efforts are also needed.  The UNEP has suggested 16 key measures to reduce methane  and BC emissions, and has started a Climate and Clean Air Coalition (CCAC) programme (https://www.ccacoalition.org/en). In order to achieve goals of the UNEP-CCAC by 2030, SLCP networking is much needed in south Asian region² which can focus upon the following objectives-

To provide a systematic network of SLCP measurements with required QA/QC.

To provide research-based policy development for adaptation and mitigation of SLCPs in the south Asia.

To develop co-ordination and collaboration among the regional researchers and institutions.

To develop capacity building in the region.

References

1. Agrawal M, Rajput M, Singh RK (2003) Use of ethylenediurea to assess the effects of ambient ozone on Vigna radiata. Int J Biotronics 32:35–48 
2. CCAC. 2021. Short-Lived Climate Pollutants (SLCPs). Climate and Clean Air Coalition. https://www.ccacoalition.org/en/content/short-lived-climate-pollutants-slcps. Accessed on April 21, 2024.
3. CSE. 2020. Ozone levels increased during lockdown, says CSE’s new analysis of air pollution levels in 22 cities across India. https://www.cseindia.org/analysis-of-air-pollution-levels-in-22-cities-across-india-10231. Accessed on April 27, 2024.
4. Dentener F. et al. 2020. Lower air pollution during COVID-19 lock-down: improving models and methods estimating ozone impacts on crops. Phil. Trans. R. Soc. A.37820200188. http://doi.org/10.1098/rsta.2020.0188.
   CrossRef
5. Emberson L. 2020. Effects of ozone on agriculture, forests and grasslandsPhil. Trans. R. Soc. A.37820190327http://doi.org/10.1098/rsta.2019.0327.
   CrossRef
6. Kim, S.-W., Cho, C., & Rupakheti, M. 2021. Estimating contributions of black and brown carbon to solar absorption from aethalometer and AERONET measurements in the highly polluted Kathmandu Valley, Nepal. Atmospheric Research, 247: 105164. doi:10.1016/j.atmosres.2020.105164.
   CrossRef
7. Kulshrestha, U. 2020. Reason for High Levels of Ozone in Delhi during COVID-19 Lockdown. NCR Air Pollution, JNU ENVIS RP Newsletter 24 (4), 3-4.
8. Mishra M. and Kulshrestha U.C. 2021. Source Impact Analysis Using Char-EC/Soot-EC Ratios in the Central Indo-Gangetic Plain (IGP) of India. Aerosol and Air Quality Research, 21 (9), https://doi.org/10.4209/aaqr.200628.
   CrossRef
9. Mishra, M. and Kulshrestha, U., 2016. Chemical characteristics and deposition fluxes of dust-carbon mixed coarse aerosols at three sites of Delhi, NCR. Journal of Atmospheric Chemistry, pp.1-23.
   CrossRef
10. Satheesh, S. and Ramanathan, V. 2000. Large Differences in Tropical Aerosol Forcing at the Top of the Atmosphere and Earth’s Surface. Nature. 405: 60–63.
    CrossRef
11. UNEP-WMO, 2011. Integrated Assessment of Black Carbon and Tropospheric Ozone https://www.ccacoalition.org/en/resources/integrated-assessment-black-carbon-and-tropospheric-ozone. Accessed on January 22, 2022.
12. USEPA, 2011. Black Carbon Research And Future Strategies. https://www.epa.gov/sites/default/files/2013-12/documents/black-carbon-fact-sheet_0.pdf. Accessed on April 21, 2024.
13. USEPA, 2012. Reducing Black Carbon Emissions in South Asia: Low Cost Opportunities. https://www.ccacoalition.org/en/resources/reducing-black-carbon-emissions-south-asia-low-cost-opportunities. Accessed on April 21, 2024.
14. Verma K and Kulshrestha U.C. 2021.A Study of Socio-Economic Impact of Soft Approaches of Climate Adaptation using Changing Fuel Practice in Indoor Air at Rural Sites in India. Current World Environment. http://dx.doi.org/10.12944/CWE.16.2.11. 
    CrossRef