The hydroxyl radical (OH) is a primary oxidant in the atmosphere, controlling the lifetimes of many gases that impact both air quality and climate change. For example, the OH radical reacts with volatile organic compounds (VOCs), usually leading to the formation of peroxy radicals, both HO2 and organic peroxy radicals (RO2), which in the presence of nitrogen oxides (NOx), can lead to the production of ozone and secondary organic aerosols (SOA) in the atmosphere, the primary components of photochemical smog. Because of its central role in atmospheric chemistry, measurements of OH and HO2 (together HOx) can provide a critical test of our understanding of this chemistry.
However, the importance of the OH radical in the chemistry and air quality of indoor environments is poorly understood. Given that people spend approximately 90% of their time indoors, improving our understanding of the factors that control indoor air quality is important in order to assess risk factors associated with exposures to indoor air pollutants. Similar to the outdoors, OH can initiate the oxidation of indoor concentrations of VOCs, leading to the production of aldehydes, ketones, acids, and SOA, which can all impact human health and welfare. As a result, the OH radical may be a significant oxidant in indoor environments, converting VOCs into SOA and potentially more toxic compounds.
This project will involve comprehensive measurements of OH and peroxy radical concentrations in a variety of indoor environments designed to improve our understanding of the reactive transformation of chemicals in indoor air, including the production of secondary aerosols. The project will address the following questions:
- What is the spatial distribution (both horizontal and vertical) of radical concentrations inside various indoor rooms, especially in the near-surface environment?
- What is the relative importance of photolytic vs. non-photolytic sources of radicals in different indoor environments?
- How well do we understand total radical sinks in indoor environments?
- How do outdoor concentrations of radical precursors impact indoor radical chemistry?
- How do indoor radical concentrations impact aerosol formation and growth?
Measurements and Instrumentation:
Radical concentrations will be measured using the Indiana University Laser-Induced Fluorescence-Fluorescence Assay by Gas Expansion Instrument (IU-FAGE). In addition to radical concentrations, measurements of several important OH radical precursors, such as nitrous acid (HONO) as well as measurements of the total rate of OH chemical removal, will be done to provide important information on indoor radical sources and sinks. Simultaneous measurements of aerosol formation and growth starting from molecular length scales (< 3 nm in diameter) will also be conducted to provide information on the importance of indoor radical chemistry on the production of SOA.
Initial measurements will be conducted at the Indiana University Research and Teaching Preserve field lab, allowing simultaneous measurements of both indoor and outdoor concentrations. Based on the results of these initial measurements, more detailed experiments will be designed for intensive measurements of radicals and SOA production at the Purdue University Natural Ventilation (NV) Chamber at the Bowen Laboratory, the Living Laboratories (LLs) at the Ray W. Herrick Laboratories, and at the ReNEWW House (Retrofit Net Zero: Energy – Water – Waste). These subsequent experiments would allow more detailed measurements as a function of controlled ventilation and lighting conditions and human occupancy.
The Purdue University NV Chamber exterior (left), the Herrick LLs open-plan office space (middle), and the ReNEWW house (right).
- Philip S. Stevens (PI): James H. Rudy Professor, School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington
- Brandon E. Boor (co-PI): Assistant Professor, Lyles School of Civil Engineering and Division of Environmental and Ecological Engineering, Purdue University