Speaker: Katie Tuite
Institution: UCLA
Abstract:
Air pollution is a global environmental problem that has negative impacts to human health and earth’s climate. Two environments that have particularly high concentrations of pollutants are urban regions and wildfire smoke plumes. Many harmful pollutants, such as ozone and particulate matter, are formed through atmospheric chemistry, which is driven by the hydroxyl radical (OH). Nitrous acid (HONO) is one of the most important OH precursors in the polluted atmosphere. Despite its importance, there remain large uncertainties in the emission and chemical sources of HONO, which leads to an underestimation of HONO and OH concentrations in atmospheric models.
In this talk, HONO observations from two field studies are interpreted to better quantify its sources and impact on OH levels in urban regions and wildfire smoke plumes. We developed a new one-dimensional chemistry and transport model to perform mechanistic studies of HONO chemistry in these complex atmospheric systems. Our results show that surface chemistry at the ground is the dominant source of HONO to the urban boundary layer. HONO photolysis is the main OH source near the surface but this impact decreases with altitude. In young wildfire smoke plumes, high HONO levels are a consequence of large direct emissions, allowing it dominate OH production. HONO is preserved in the plume center due to low photolysis rates, providing a reservoir of HONO downwind of the burning site. Chemical HONO formation on aerosol plays a minor role in young smoke, but its significance as a source increases as the smoke ages.