For years, scientists tracking air pollution in Southeast Asia have been reading the wrong map. Now, a team of researchers in Vietnam may have uncovered why cities like Ho Chi Minh City have struggled to pinpoint exactly where their smog is coming from — and the answer lies in a chemical that disappears before anyone can measure it properly.
Levoglucosan is the tracer scientists use to track biomass burning, the combustion of wood, charcoal, and agricultural residues that pumps fine particulate matter (PM2.5) into the air. It's the compound that tells researchers whether a city's haze originates from rural crop fires, home cooking, or something else entirely. But according to a new study by researchers at Osaka Metropolitan University, approximately 88% of levoglucosan is lost before it can be measured, degraded by sunlight and evaporation as it drifts through the atmosphere.
"Conventional analyses that do not account for this loss risk misidentifying emission sources," said Associate Professor Yusuke Fujii of the Graduate School of Sustainable System Sciences. In tropical cities like Ho Chi Minh City, where intense sunlight accelerates chemical breakdown, this loss is especially pronounced — and especially misleading.
When the Osaka team corrected their measurements to account for the missing levoglucosan, the picture of Ho Chi Minh City's pollution sources shifted dramatically. Previous analyses had pointed to crop residue and grass burning from rural areas as the primary culprits. But after factoring in atmospheric degradation, the data told a different story: the city's smog was actually being driven primarily by hardwood and charcoal burning — most notably from cooking.
"In Vietnam, urban air pollution remains a serious concern," said Ngoc Tran, a Vietnamese researcher on the team. "There is a strong need to clarify the detailed contributions of these sources, specifically what is being burned and where, in order to develop effective mitigation strategies."
The implications stretch well beyond Vietnam. If other cities have been misattributing their pollution sources, they may also have been misdirecting the financial resources meant to clean the air. The study, published in the journal ACS Omega, suggests that by integrating atmospheric degradation corrections with local environmental conditions, researchers worldwide can finally distinguish between sources that previously blurred together.
"This approach will contribute to improving the accuracy of source apportionment in urban areas worldwide," Fujii said.
Put simply: better measurements lead to better decisions. For cities grappling with choking smog and finite budgets, knowing exactly what is burning — and where — could reshape how governments invest in cleaner alternatives, from improved cookstoves to updated industrial regulations. The science of clean air just got sharper.