Worldwide, air pollution in indoor and outdoor environments results in approximately 8 million human deaths every year. Reducing the adverse human health effects of air pollutants requires a detailed understanding of their sources and fate. Outdoors, most pollutants are secondary – formed from atmospheric oxidation chemistry of primary (emitted) pollutants. Hydroxyl and ozone are the most abundant tropospheric oxidants, but chlorine atoms are much more reactive and can oxidize functional groups or whole molecules that are resistant to the weaker common oxidants. This can increase the formation of harmful secondary pollutants including particulate matter (PM) and ozone. Indoors, cleaning and disinfection with bleach is a main source of chlorine and resulting chemistry. Indoor air quality is especially important considering that we spend approximately 90% of our time indoors.
Ambient measurements conducted by our group in New Delhi, India periodically show extremely high concentrations of particulate chlorine, implying an especially important role of chlorine chemistry in this highly polluted megacity. Laboratory experiments show efficient formation of PM from chlorine-initiated oxidation of different hydrocarbon precursors. Using measurements from a high resolution time of flight chemical ionization mass spectrometer, we are able to track several generations of oxidation chemistry leading to the formation of organic particulate matter, as well as explore the molecular composition of PM. Chlorine-initiated reactions generally form PM at a higher yield than OH-initiated reactions, and the PM formed is often more oxygenated. Organochlorides form from all precursors investigated, even when the initial oxidation occurs via hydrogen-abstraction. In indoor environments we see that bleach cleaning alters gas and particle-phase composition. We are also evaluating the interaction of disinfectants with face masks and resulting inhalation of disinfection byproducts. Overall, our measurements show important impacts of chlorine on air quality in indoor and outdoor environments.
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