Research sheds light on the underprediction riddle of biomass burning Oxidized organic aerosol is a major component of ambient particulate matter, substantially impacting climate, human health, and ecosystems. Oxidized aerosol from biomass burning is especially toxic, known to contain a large amount of species that are known carcinogens, mutagens. Inhaling biomass burning particles also cause oxidative stress and cause a wide range of diseases such as heart attacks, strokes, and asthma. Oxidized aerosol primarily forms from the atmospheric oxidation of volatile and semi-volatile compounds emitted by sources like biomass burning, resulting in products that readily form particulate matter. Every model in use today assumes that oxidized aerosol forms in the presence of sunlight, and that it requires days of atmospheric processing to reach the levels observed in the environment. Naturally this implies that oxidized aerosol forms in the daytime and mostly during periods with plentiful sunshine, such as in summer.