Researchers from the CAS Institute of Earth Environment, Nanjing University and Louisiana State University have found that combustion-derived water vapor CDW might worsen winter air quality. Using isotope distribution as markers in atmospheric physical and chemical data from Xi’an, they found that CDW constituted 6.2% of the atmospheric moisture on average and its fraction was positively correlated with the concentration of particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5) as well as relative humidity during the periods of rising PM2.5 . Feeding these data into models of a typical heavy haze eposide, they concluded that the additionally added PM2.5 by combustion-derived water during a heavy haze episode was 2.8% on average, with the highest percentage of 8%.

The study takes into account CDW from the burning of natural gas, gasoline, or coal but might also be relevant for a future “hydrogen society” where hydrogen cars and hydrogen-based fuel cells increase the water content of the atmosphere.