Why is it in the news?

• As the southwest monsoon recedes and winter approaches, Delhi’s air quality has significantly deteriorated. Recently, the city and surrounding areas have consistently recorded particulate matter (PM 2.5) levels exceeding 300, categorizing the air quality as ‘very poor.’
• Forecasts indicate that this decline may worsen in the coming days, following the established pattern of increased pollution associated with the seasonal burning of farm stubble, primarily from Punjab.

Contribution of Stubble Burning to Air Pollution

• Stubble burning is the practice of farmers burning remnants of paddy stalks post-harvest, which is often the quickest method for clearing fields. Farmers in Punjab and Haryana face a limited window in October and November to prepare for winter crops, making burning a common choice.
• While the environmental consequences of this practice have been recognized since the 1990s, its significant link to deteriorating air quality in Delhi has only been quantified in recent years.
• Studies using advanced instruments have consistently shown that wind patterns from these states contribute to pollution levels in Delhi, with stubble burning responsible for an estimated 22% to 35% of air quality deterioration during the peak burning period.

Observations on Air Quality Trends

• Research indicates that the transition from monsoon to winter results in reduced wind speeds, causing pollutants to settle closer to the ground instead of dispersing.
• Consequently, even minor sources of pollution, such as stubble burning, can significantly impact the air quality index (AQI) in Delhi.
• It’s noted that nearly 55% of Delhi’s pollution originates from outside its borders, leading to drastic fluctuations in AQI based on external conditions.

Urban Emissions and Their Role

• Although stubble burning is a major contributor, it is not the sole factor affecting air quality. A report by Urban Emissions highlights that from 2016 to 2023, Delhi’s air quality improved overall but consistently remained above the ‘poor’ threshold.
• Despite a dramatic decrease in stubble burning incidents in Punjab and Haryana, Delhi’s AQI has remained in the ‘very poor’ and ‘severe’ categories during winter months when stubble burning ceases. This suggests other significant sources of pollution are at play.

Other Contributing Factors to Pollution

• On October 25, stubble burning accounted for approximately 15% of Delhi’s air pollution, while emissions from transport contributed around 18%.
• Studies show that secondary inorganic aerosols (SIA), which originate from chemical reactions involving sulphur dioxide, nitrogen oxides, and ammonia, account for the majority of PM 2.5 levels in Delhi.
• SIA contributes around 32% to the winter pollution load, with biomass burning accounting for 24% and vehicular emissions for 17%.
• Policymakers have increasingly recognized the need for a coordinated approach across multiple states, advocating for a comprehensive response to tackle the air pollution crisis effectively.