Understanding Nitrous Acid Sources on Atmospherically Relevant Surfaces

EPA Grant Number: F13B10142
Title: Understanding Nitrous Acid Sources on Atmospherically Relevant Surfaces
Investigators: Scharko, Nicole Katherine
Institution: Indiana University - Bloomington
EPA Project Officer: Lee, Sonja
Project Period: August 25, 2014 through August 25, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Environmental Science

Objective:

Despite the importance of HONO, little is known about the mechanisms by which it is formed. Daytime HONO formation is of particular interest because current atmospheric models under-predict daytime HONO concentrations measured in the field. There is speculation that daytime HONO may stem from nocturnal mechanisms. The objectives of this study are to characterize daytime and nocturnal sources of HONO by measuring key parameters, such as reaction efficiencies and uptake coefficients. These parameters are essential for accurate air quality predictions.

Approach:

The project will study a potentially important daytime source of HONO by monitoring the formation of gas phase nitrogen dioxide and HONO from the photolysis of nitric acid and nitrate adsorbed to environmentally relevant surfaces (components of soil, suspended particulate matter and aerosols). Photochemical reaction chambers and flow tubes will be used to study the kinetics and mechanism of this chemistry. Three instrumental techniques will be used: Fourier transform infrared spectroscopy to study oxides of nitrogen adsorbed to surfaces and emitted into the gas phase; chemical ionization mass spectrometry to measure HONO emitted from the surfaces into the air; and cavity-enhanced absorption spectroscopy to measure gas phase nitrogen dioxide and HONO simultaneously. Thermal sources of HONO also will be examined by quantifying the amount of HONO generated by the hydrolysis of nitrogen dioxide on soil as a function of relative humidity, nitrogen dioxide concentration and temperature.

Expected Results:

The kinetics and mechanisms associated with production of HONO from nitrate photolysis on environmentally relevant surfaces will provide important insights into the mechanism of a potentially important daytime source of HONO. As for the nocturnal source, hydrolysis of nitrogen dioxide on surfaces has been attributed to the accumulation of HONO during the night. Uptake coefficients for nitrogen dioxide on soil and the individual components of the soil will be determined; the approach taken will provide a way to eliminate confounding factors associated with studying such complex systems and allow more precise study of the mechanism of HONO production. The approach is unique because previous methods of studying these problems have been limited to working under vacuum and in the absence of air and water. This work is expected to yield more atmospherically relevant results that can be used for predictions of air quality and climate.

Potential to Further Environmental/Human Health Protection

Understanding mechanisms of HONO formation, during both the daytime and nighttime, will improve the atmospheric chemistry models used by policy-makers to create effective air quality control strategies. Effective policy that saves lives and reduces health care costs associated with exposure to air pollution is possible only when the model results are correct for the right reasons.

Supplemental Keywords:

nitrogen dioxide, nitrous acid, photochemistry

Progress and Final Reports:

  • 2015
  • Final