Collaborative Research: Understanding Emission Sources and Sinks of Nitrous Acid in North American Forests

Indiana University, Bloomington IN

Investigators

Abstract

This project focuses on land-atmosphere interactions and the mechanisms by which nitrous acid (HONO) and other nitrogen oxides emitted from soils influence the oxidizing capacity of the atmosphere. The experimental plans include the use of growth chambers under controlled conditions combined with field data to study the uptake of HONO onto leaves from a range of tree species that dominate major forested regions across North America. Since HONO is not well represented in chemical transport models, improvements in understanding HONO sources and sinks are expected to have important implications for improving air quality models and for determining the lifetime of some greenhouse gases, such as methane, in the atmosphere. This effort combines expertise in atmospheric chemistry, microbial ecology, and modeling with unique analytical capabilities for measuring HONO soil emissions. The central hypothesis of this proposal is that variations in below-canopy hydrogen oxide radical (HOx) cycling and ozone levels in forested regions are driven by the variability of soil emissions of HONO (SHONO) and nitrogen oxide (NO) (SNO), that depend on season, edaphic properties, aboveground vegetation surfaces, and belowground nitrogen cycling that is mediated by microbe-plant interactions. Preliminary data show that high SNO has a significant impact on below canopy HOx in a forested environment, that NOy (the sum of reactive nitrogen oxides) fluxes are linked to forest composition, and that spatial variability in NOy fluxes can be mapped across the continental U.S. using forest inventory plots. The objectives of the research are to: (1) Establish geospatial trends in SHONO across U.S. forests; (2) Carry out field campaigns to measure SHONO in mixed deciduous forests; and (3) Quantify uptake of HONO by leaf and soil surfaces. The project will support a full-time postdoctoral researcher and a graduate student who will receive training in state-of-the science analytical and modeling methods. Undergraduate students will be directly involved in the research as part of Indiana University’s Groups Summer Research Experience Program, which gives entering first-year students research experience and skills to excel in STEM majors. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.