Jacob Koshy’s new book links nitrogen to India’s pollution crisis

Pollution risks in the Indo-Gangetic Plain

The book examines the pollution crisis within the Indo-Gangetic Plain, a region spanning northern India. This area is a 2,500-kilometre arc that stretches from Pakistan to Bangladesh and supports a population of nearly half a billion people.

Nitrogen's role in India's PM2.5 burden

The same organization found that secondary pollutants account for almost 41% of fine particles in Delhi's air during winter.

Professor Srinidhi Balasubramanian of the Indian Institute of Technology Bombay estimates that 80% to 85% of ammonia in India originates from agriculture, with the remainder from industry and fertiliser plants. Research from 2021 by Professor Balasubramanian indicates that agriculture is responsible for approximately 80% of global ammonia emissions.

According to Professor Balasubramanian, ammonia alone represents about 25% of India's PM2.5, while the total secondary fraction accounts for roughly 55% of the national balance compared to 45% primary.

IIT-K research on aerosol composition

Sachchida Nand Tripathi founded the National Aerosol Facility at the Indian Institute of Technology, Kanpur, in 2003. A 2014 study from this laboratory documented four years of continuous measurements of nitrogen oxides, sulfur dioxide, ozone, and carbon monoxide to establish winter loading patterns in the Indo-Gangetic Plain.

During winter, cold temperatures and a planetary boundary layer compressed below 400 metres trap precursor gases, creating conditions that convert nitrogen oxides into ammonium nitrate particles. While gravimetric monitoring is the international benchmark for measuring particulate matter, it is limited to producing only one or two readings per week.

This mass spectrometer measures non-refractory components of particulate matter, including ammonium, nitrate, chloride, sulphate, and various organic constituents.

Identifying pollution sources via chemical fingerprints

Tripathi explains that researchers distinguish between non-refractory components measured by a mass spectrometer and refractory components, such as soot and metals, measured by a metal monitor. Combining these data sets creates unique chemical fingerprints that allow researchers to identify specific pollution sources. Machine learning models then integrate these unique chemical combinations to deduce the specific source of particulate matter.

Severe pollution events are characterized by secondary organic aerosols from vehicle exhaust along with inorganic aerosols, specifically ammonium nitrate and ammonium chloride. Ammonium chloride accounts for an average of 40% of aerosol liquid water in Delhi, which promotes further secondary aerosol formation and worsens haze through a feedback loop.

Road traffic is identified by a unique combination of soot, organics, nitrogen oxides, and metals like nickel and zirconium, which originate from tyre friction against the road surface. Coal plants are identified by the presence of lead and selenium signatures alongside sulphate and soot, as these metals are present in the coal feedstock.

Agricultural plastic mulch and soil contamination

Agricultural plastic mulch, first introduced in the early 1950s, has seen widespread adoption in modern farming. The United States and Japan were among the first countries to commercially promote polyethylene mulch films for horticultural crops in the 1960s. In China, the area covered by these films expanded from 15,400 hectares in 1981 to approximately 3.3 million hectares in 1990.

Manufacturers produce mulch films by blending polymer feedstocks with additives and colorants, followed by melt plasticization and extrusion processes. Farmers adjust colors such as black, white, or silver to regulate light, suppress weeds, and manage soil temperature. Mechanized film-laying technology has enhanced production efficiency and facilitated widespread adoption. These films improve crop yield and quality by optimizing the soil microenvironment, suppressing evaporative water loss, and improving light interception.

In contrast, organic farming standards prohibit the use of mineral nitrogen fertilizers and include capped nitrogen inputs. A 2025 study by Wang et al. examined water and nitrogen utilization in soybean-maize strip intercropping.

Residues in farmland soil can increase levels of microplastics and phthalate esters, which leads to crop contamination. Residual films also adsorb pesticides and hinder their degradation, facilitating the entry of chemicals into the soil.

A review published on 5 November 2026 analyzed 247 studies on agricultural plastic mulching selected from an initial pool of 2,157 records. A 2025 study by Nie et al. investigated the combined pollution effects of high-density polyethylene and cadmium on nitrogen storage in coastal wetland soil.