| dc.description.abstract | Atmospheric aerosol, liquid or solid particles suspended in air, has profound implications for air quality, climate, and human health. Secondary organic aerosol (SOA) formed from photochemical oxidation of volatile organic compounds (VOCs) represents the dominant constituent of tropospheric fine aerosols. However, the chemical complexity relevant to gaseous oxidation and subsequent gas-to-particle conversion poses enormous challenges in elucidating the formation and impacts of atmospheric particles.
In the first part of this dissertation, we performed experiments by exposing sub-micrometer seed particles to glyoxal or methylglyoxal in the presence/absence of ammonia and formaldehyde inside an environmental chamber. We show significantly more efficient growth and browning of aerosols upon exposure to methylglyoxal than glyoxal under atmospherically relevant concentrations, and non-volatile oligomers and light-absorbing nitrogen-heterocycles are identified as the dominant particle-phase products. The distinct aerosol growth and optical properties are attributed is attributed to carbenium ion-mediated nucleophilic addition, interfacial electric field-induced attraction, and synergetic oligomerization involving organic/inorganic species.
Second, we investigate multi-generation SOA production from toluene and m-xylene by simultaneously tracking the evolutions of gas-phase oxidation and aerosol formation in a reaction chamber. The results reveal that aerosol growth and browning are mainly attributed to earlier generation products consisting of the di-carbonyl and carboxylic functional groups. We conclude that toluene/m-xylene contribute importantly to SOA formation via primarily dicarbonyls and organic acids resulting from their prompt and high yields from oxidation as well as their unique functionalities for participation in particle-phase reactions.
Third, to assess the role of respiratory aerosols in the transmission of infectious diseases, the pandemic trends during the earlier COVID-19 pandemic in several epicenters worldwide and in the United States were analyzed. The transmission and intervention jointly shape the pandemic trends from January to May 2020, showing that airborne transmission and face covering play the dominant role in spreading the virus and flattening the total infection curve, respectively.
Our findings explain atmospheric measurements of rapid SOA formation especially under polluted urban conditions and highlight the importance for functionality-reactivity relationship for SOA production from condensable oxidized organics. Additionally, we show that aerosols play an important role in transmission of infectious diseases. | en |
