THIRUVANANTHAPURAM: A two-year study by researchers from the KSCSTE-National Transportation Planning and Research Centre (NATPAC), Thiruvananthapuram, and the Kerala University has found that people spending time near busy traffic junctions during peak afternoon hours face a significantly higher health risk—one that combines the dangers of air pollution and heat stress which together put one’s heart and lungs at risk.
The findings come at a critical time. Kerala is currently experiencing one of its most intense pre-monsoon heatwaves in recent years, with the India Meteorological Department (IMD) issuing alerts across several districts and health authorities advising people to avoid outdoor exposure between 11am and 3pm.
The NATPAC study adds a sobering dimension to that warning—for a large section of the population that simply cannot stay indoors.
The study, conducted across 2022 and 2023 at two monitoring stations in Thiruvananthapuram—Plamoodu, a dense urban traffic junction, and Karyavattom, a more open suburban campus area—tracked PM2.5, the fine particulate matter generated by vehicle exhaust, road dust, and atmospheric chemical reactions, alongside the Heat Index which combines temperature with humidity to reflect how hot conditions actually feel to the human body.
The central finding is that these two stressors amplify each other.
Integrated policy framework suggested
“Heat stress raises breathing rates, increasing inhalation of fine particles. Those particles then trigger inflammation that impairs the body’s ability to regulate temperature, compounding strain on the respiratory and cardiovascular systems,” said Tinku Casper D’Silva, Scientist B, Traffic Engineering andSafety Division, KSCSTE-NATPAC.
To measure this combined burden, researchers developed a Joint Exposure Index, which captures the interaction between heat stress and particulate pollution. At Plamoodu, nearly one in five daytime hours during the pre-monsoon season falls into the high-risk category. At Karyavattom, it is approximately one in 10.
The most dangerous window is consistently between 10am and 3pm, precisely the period flagged by current heat alerts. Though both sites technically meet India’s national air quality standards, PM2.5 concentrations already exceed WHO guidelines by nearly six times, said Salom Gnana Thanga Vincent, Professor and Head, Department of Environmental Sciences, University of Kerala.
Dense buildings at Plamoodu also block incoming sea breezes, trapping heat and pollutants at street level in what the researchers describe as a “pollution bowl”.
The populations most at risk are autorickshaw drivers, bus conductors, delivery riders, roadside vendors, and pedestrians — those for whom the high-risk afternoon window is their working day. Short-term consequences include dehydration, heat cramps, and respiratory distress, while prolonged exposure raises risks of cardiovascular disease and premature mortality.
The study recommends shaded bus bays, green corridors along major junctions, regulated traffic idling during peak hours, and an integrated policy framework that addresses heat stress and air pollution together rather than as separate challenges.
Researchers plan to expand the work by mapping the threat on major roads across the state with the support of the State Disaster Management Authority.
What is Joint Exposure Index (JEI)?
Single risk score that combines two threats: PM2.5 (air pollution) and Heat Index (felt temperature)
Heat stress raises breathing rates, increasing inhalation of fine particles. The particles trigger inflammation that impairs the body’s ability to regulate temperature, compounding strain on the respiratory and cardiovascular systems.
Captures how the two hazards multiply each other
The danger window
Highest risk: 10am to 3pm daily
Worst months: March, April, May