Effects of Ammonia on Secondary Organic Aerosol Formation in a Changing ClimateEPA Grant Number: R835881
Title: Effects of Ammonia on Secondary Organic Aerosol Formation in a Changing Climate
Investigators: Dabdub, Donald , Nizkorodov, Sergey
Institution: University of California - Irvine
EPA Project Officer: Chung, Serena
Project Period: January 1, 2016 through December 31, 2018 (Extended to December 31, 2019)
Project Amount: $701,304
RFA: Particulate Matter and Related Pollutants in a Changing World (2014) RFA Text | Recipients Lists
Research Category: Air , Climate Change
Atmospheric aerosols have a profound effect on climate by scattering and absorbing solar and terrestrial radiation and on air quality by contributing to the mass of PM2.5, a criteria pollutant controlled by EPA. Secondary organic aerosols (SOA), which result from photooxidation of volatile organic compounds (VOC), make the dominant contribution to PM2.5 by mass. The effects of various air pollutants, such as NOx (= NO + NO2), O3, and SO2, on the rate and yield of SOA formation are relatively well constrained in chemical mechanisms and implemented in air-pollution models. However, the effect of ammonia (NH3) on SOA is much less understood. Recent laboratory and field observations suggest that ammonia actively participates in formation of SOA and it also leads to chemical compounds in SOA that have unique optical properties. The main goal of this proposal is to explore systematically the effect of the reactive uptake of ammonia (NH3) by secondary organic aerosols (SOA) on the yield, chemical composition, and optical properties of anthropogenic SOA using both experimental and modeling approaches.
The following are the set of specific project objectives to meet the main goal:
- Study the reactive uptake of NH3 by SOA in chamber experiments and the effects of temperature, humidity, and NH3 levels on the yields of SOA and types of nitrogen-containing organic compounds (NOC) produced
- Conduct box model simulations of chamber experiments on NOC-containing SOA
- Introduce a new mechanism of formation of NOC in the aged SOA in an urban three-dimensional air quality model
- Quantify the effects of changing meteorological conditions and background concentrations due to climate change on SOA and NOC concentrations at urban level
- Introduce a simplified SOA chemical mechanism into a coupled meteorological-air quality model for the entire contiguous United States
- Quantify the effects of changing meteorological conditions and background concentrations due to climate change on SOA and NOC at the continental scale and estimate the feedback effects of aged SOA on meteorological conditions
We propose targeted laboratory experiments in which SOA are prepared under controlled conditions in a smog chamber, aged by ammonia, and examined with a suite of instruments that measure SOA yield, detailed molecular level composition, and optical absorption coefficient of SOA. We also propose implementation of the results of these observations into a box model that replicates chamber experiments, and into two state-of-the-art air pollution models: (1) an urban model that will evaluate the effects of ammonia and climate change on SOA with a comprehensive chemical mechanism for SOA formation, and (2) a coupled meteorological-air quality model that will evaluate the effects of ammonia and climate change on SOA formation and its feedbacks on meteorological conditions for the entire US.
Ammonia emissions are expected to increase worldwide because of the intensifying agricultural use of ammonia-based fertilizers and because of increasing temperatures. At the same time, emissions of VOC precursors are also expected to increase because of the rising trends in the global temperatures. The combination of these two trends is likely to lead to significant changes in the mass-concentrations and chemical composition of SOA. There are three major expected results: (i) elucidate the fundamental science related to ammonia and SOA dynamics; (ii) develop and implement the new science into computer code to be used by modelers; and (iii) quantify climate changes effects on SOA and brown carbon concentrations in the atmosphere.