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Research: Atmospheric Chemistry and Deposition

Pollutants released into the air can impact air quality, as well as terrestrial and aquatic ecosystems when the pollutants deposit to Earth. The Nation spends tens of billions of dollars each year to reduce air pollution in order to protect human health and the environment. Effective targeting of air pollution controls depends on having good scientific understanding of which sources, which pollutants, and which regions are contributing to the problems.

ARL conducts a world-class research program that provides information and products that directly support air quality decision-makers, air quality forecasters, and the research community. Specifically, we focus on improving measurements and monitoring the exchange of pollutants between the air and the Earth's surface and on developing and applying the next generation of forecasting and assessment tools.

ARL scientist conducting ammonia study in animal barn
ARL scientist installing instruments to measure ammonia-nitrogen concentrations in a barn populated by Angus beef cattle. Ammonia emissions from animal waste can contribute to formation of particulate matter in the air and, through atmospheric deposition processes, contribute to excessive nitrogen (a nutrient) loadings to terrestrial and aquatic environments. Photo: NOAA

What We Do

Air-Surface Exchange of Pollutants
Particles and gases released into the air are exchanged with the Earth's surface — termed air-surface exchange. ARL focuses on specific chemicals, including nitrogen, sulfur, and mercury compounds, which can have a significant impact on our environment — and in the case of mercury — human health.

Acid Rain and Nitrogen Fertilization
Sulfur and nitrogen compounds contribute to the acidification of freshwater systems, and in the case of nitrogen, to the over-fertilization of coastal and estuarine waters. In coordination with the National Atmospheric Deposition Program (NADP), we conduct long-term, research-grade deposition monitoring of these and other compounds. Our research network, called the Atmospheric Integrated Research Monitoring Network, or AIRMoN, provides data to better undertand the sources of these compounds and to evaluate the effectiveness of existing regulatory emission controls. To complement the research monitoring, we conduct short-term field studies that test emerging chemical measurement technologies and improve the understanding of the atmospheric and terrestrial processes and factors (i.e., wind, temperature, surface roughness) controlling air-surface exchange of these compounds. Data from both the AIRMoN and our field studies are used to improve and evaluate modeling products.

Mercury Contamination
Mercury is known to adversely affect the nervous system, particularly those of fetuses and young children. People are exposed to mercury primarily by eating contaminated fish and shellfish. This contamination occurs primarily from atmospheric mercury entering into aquatic ecosystems, which is then taken up by fish and other aquatic organisms. Terrestrial animals are also exposed to mercury. In coordination with the NADP, we operate long-term intensive ambient air mercury monitoring stations. These are part of a national monitoring network designed to address total mercury deposition across the country. We also conduct short-term intensive studies at select locations around the world. Data collected are also used to interpret and evaluate our mercury modeling system—a special version of the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) Model—which tracks mercury emission sources, transport, and deposition.

The HYSPLIT-Hg model starts with a mercury emissions inventory; then utilizes meteorological data to estimate the atmospheric dispersion of mercury from each source. Chemical reactions in the air, phase- partitioning of the mercury, and wet and dry deposition are then simulated by the model. A key feature of HYSPLIT-Hg is that it can estimate the overall atmospheric concentrations and deposition arising from mercury emissions and at the same time keep track of the individual contributions of each source to the overall totals.

Air Quality Forecast Products
Although air quality has improved dramatically in the U.S., about forty percent of the population still live in areas affected by air pollution. The primary air quality problems are elevated levels of ground-level ozone (O3) and fine particulate matter (PM2.5 ) which can lead to respiratory and cardiovascular problems and tens of thousands of premature deaths each year. Accurate air quality forecasts enable communities to take actions that can reduce the severity of episodes of poor air quality and also enable individuals to take protective actions that limit their own exposure to unhealthy air.

ARL scientists evaluate and improve air quality models used by NOAA's National Weather Service (NWS) to operationally predict concentrations of O3 and PM2.5. ARL performs rigorous comparisons of model predictions with actual atmospheric measurements. Based on the knowledge gained from these evaluations, ARL adds or enhances specific model processes or input data sets to better represent emissions of air pollutants and the physical and chemical complexities that occur in the atmosphere. The continuous model evaluation and improvement cycle conducted by ARL scientists leads to better NWS operational air quality forecast products. This work supports air quality planners and managers, air quality forecasters, and the research community.

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Modified: August 4, 2016
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