Thesis (Ph.D.) - Indiana University, O’Neill School of Public and Environmental Affairs, 2021Hydroxyl (OH), hydroperoxy (HO2), and peroxy (RO2) radicals are key to atmospheric oxidation, critically altering the chemistry of the air we breathe. Radical reactions initiate oxidation of volatile organic compounds (VOCs), which in the presence of nitrogen oxides (NOx) can form ozone and secondary organic aerosols (SOA)—air pollutants affecting human health and welfare in ambient and indoor environments. In ambient environments with high mixing ratios of biogenic VOCs and low mixing ratios of NOx, measurements using our current instrumental technique for radicals have shown discrepancies with modeled predictions. Here, these discrepancies were investigated during the Indiana Radical, Reactivity, and Ozone Production Intercomparison II (IRRONIC II) field campaign. Intercomparisons between different radical measurement techniques were done (1) between their individual calibration techniques and (2) between ambient radical measurements of each instrument. All instruments proved able to measure OH, HO2, and RO2 at levels encountered in forests and agreed with each other within stated uncertainties. The agreement between measurements in this unpolluted, forested area with elevated levels of biogenic emissions instilled confidence in the accuracy of our radical measurement techniques. Previously, there have been few direct measurements of radicals in indoor environments, compared to ambient environments. However, these radicals critically affect mechanisms involving indoor pollutants, e.g., VOCs, ozone, and SOA. In this study, radical chemistry involving terpene-based and bleach cleaners were investigated during HOMEChem (House Observations of Microbial and Environmental Chemistry) and iRACE (Indoor Radical and Aerosol Chemistry Experiments). In iRACE, secondary oxidation products, radicals, and new particle (aerosol) formation were observed immediately after using a terpene-based cleaner. Radical and aerosol concentrations reached levels comparable to outdoor traffic-impacted areas, emulating “indoor smog” for 10–15 minutes and respiratory tract deposition comparable to that from the inhalation of traffic-associated aerosol in an urban street canyon. Meanwhile, in HOMEChem, indoor sunlight was found to induce bleach-initiated radical chemistry and enhance radical production indoors, similar to levels expected outdoors. These developments in our understanding of secondary chemistry-driven indoor air pollution (as opposed to direct emissions) serve to help inform regulations regarding cleaning product formulations and improve our cleaning practices indoors.