Key Details
The UNDP brief, The Overlooked Pollutant brings together evidence on heat, health and crop losses.
Heatwave exposure: An analysis of 188 heatwave events in India found ozone frequently above the WHO’s peak-season guideline of 60 µg/m³, reaching 85–110 µg/m³ in northern regions.
Wheat losses: Across the Indo-Gangetic Plain districts studied in 2019–2021, ozone exposure was estimated to reduce wheat yields by 9–13%—a production loss of 3.4 million tonnes, valued at nearly US$1 billion.
Health burden: The brief shows a substantial rise in India’s rate of deaths attributable to ambient ozone exposure between 1990 and 2023. Ozone can worsen respiratory illness, particularly during hot weather.
Climate link: Ozone in the lower atmosphere has contributed an estimated 0.23°C to present-day global warming.
Proposed response: Reduce nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) that drive local ozone peaks, alongside methane that contributes to ozone across wider regions.
Hot, Sunny Days Can Conceal a Pollution Risk
Unlike the protective ozone layer high above Earth, ground-level ozone is an air pollutant. It is not emitted directly: it forms when pollutants from sources such as vehicles, industry and fuel use react in sunlight. Higher temperatures can accelerate that process. Ozone may therefore rise during heatwaves even when the air looks clear, adding respiratory risk when people are already exposed to extreme heat.
The Damage Extends from Lungs to Wheat Fields
Ozone enters plant leaves and impairs photosynthesis, reducing growth and yields. The 9–13% wheat-loss estimategives this less visible damage an economic scale for the districts studied; it should not be read as an estimate for all Indian wheat production. The brief also cites modelling that projects greater ozone-related damage to Indian wheat and rice as temperatures rise.
These losses make ozone relevant to farm incomes and food security, not only urban air quality. The brief further notes that ozone can weaken forests’ ability to absorb carbon and disrupt the scent trails insects use to find flowers.
Cutting One Pollutant Is Not Enough
Evidence reviewed by UNDP shows why ozone requires its own strategy: particulate pollution can fall while ozone rises. Local ozone formation depends on the balance of NOₓ and VOC emissions, sunlight and weather. Controls therefore need to reflect local conditions rather than assume that any single emissions cut will produce the same result everywhere. Methane reductions can help lower the wider background level of ozone while also limiting near-term warming.
Policy Relevance
For India, the brief points to a gap between treating ozone as an air-quality reading and addressing its combined effects on heat vulnerability, respiratory health and agriculture. Monitoring ozone alongside its precursor pollutants — and assessing crop exposure as well as urban exposure — would give environment, health and agriculture authorities a clearer basis for action.
The practical choices differ by place. Cities may need coordinated NOₓ and VOC controls across transport and industry, plus health alerts on high-ozone days. Reducing methane from energy, waste and agricultural sources can address ozone over a broader area. UNDP recommends bringing these measures into air-quality plans and climate and adaptation planning.
Follow the Full Policy Brief Here: The Overlooked Pollutant: Turning Ground-Level Ozone Action into Health, Food, Ecosystems and Climate Gains