Assam’s PM2.5 breaches safety standard, western districts worst hit: IIT Delhi dataset

GUWAHATI, Sept 10: The State-level mean PM2.5 concentration over the 23-year period between 2000 and 2022 stands at 49.5 ìg/m3 in Assam, which is significantly above the national ambient air quality standard (NAAQS) of 40 ìg/m3 for annual PM2.5, according to data derived from satellite-based datasets developed by IIT Delhi.

The spatial map reveals a distinct west-to-east gradient in PM2.5 levels, with higher concentrations (exceeding 60 ìg/m3) observed in the western and southwestern districts, particularly around the border regions. In contrast, the northeastern districts show comparatively lower PM2.5 levels, often below 40 ìg/m3. This spatial pattern is influenced by factors such as proximity to industrial belts, cross-border pollution, vehicular emissions, and prevailing meteorological conditions, a draft report prepared by Climate Trends, PCBA and ASTEC stated.

According to the Central Pollution Control Board (CPCB) guidelines and international best practices, a minimum of one PM2.5 monitoring station per 10 lakh (1 million) population is recommended.

Furthermore, even for districts with a population below 10 lakh, at least one station is essential to ensure adequate spatial representation.

Applying this formula to the district-wise population of Assam, the State as a whole would require 32 PM2.5 monitors. However, when calculated at the district level (ensuring each district has at least one station), the requirement increases to 55 monitors. For example, larger districts such as Nagaon require 3 monitors, whereas smaller districts like Dima Hasao and Chirang require 1 monitor each.

Presently, there are nine Continuous Ambient Air Quality Monitoring Stations (CAAQMS), four of them for Guwahati. There are 63 other AAQM (ambient air quality monitoring) stations, but they cover only 20 districts. Proposals for setting up more stations have not got Central Pollution Control Board response so far, PCBA officials told The Assam Tribune.

“This highlights the gap between current infrastructure and required monitoring capacity, underscoring the need for a phased expansion plan to ensure every district has at least one continuous monitoring station while scaling proportionally with population size,” the report noted.

It stated that air quality management in Assam must begin with the strengthening of the monitoring network, which at present is highly limited to Guwahati and a handful of industrial towns. This urban bias leaves most districts, especially rural and peri-urban regions, unmonitored and invisible in official data. Establishing a comprehensive grid of Continuous Ambient Air Quality Monitoring Stations (CAAQMS) across all district headquarters, along with additional units in hotspots such as Digboi, Bokajan, and the Guwahati-Byrnihat corridor, would provide the backbone of a reliable system. Low-cost sensor networks can complement these stations in rural and forest-fringe areas, capturing community-level variations. The data from ground sensors should be integrated with satellite-based observations, meteorological inputs, and fire-detection tools into a State-level air quality dashboard accessible to decision-makers, researchers, and the public, it recommended.

Assam has been classified among India’s “non-attainment” States under the National Clean Air Programme (NCAP), which obligates targeted reductions in PM2.5 and PM10 concentrations by 20-30 per cent over the 2017 baseline by 2027. However, enforcement at the State and city levels remains weak, with fragmented institutional responsibility and insufficient funding, the report noted.