The U.S. Environmental Protection Agency (U.S. EPA) is embracing a whole-of-Agency approach to understand and address cumulative impacts-the totality of exposures to both chemical and non-chemical stressors-to meet its mission to protect human health and the environment, and to fulfill Executive Orders aimed at advancing environmental justice.
An introduction to atmospheric chemical mechanisms: development, usage, and future needs.
For many decades, ground-level ozone has been recognized as a pollutant that causes adverse human health effects and damages crops and ecosystems. Scientific understanding about the ambient concentrations at which such damages occur has evolved, triggering several revisions to the National Ambient Air Quality Standard (NAAQS) for ozone that gradually reduced critical thresholds. Grid-based photochemical air quality modeling systems (AQM) such as the Community Multiscale Air Quality (CMAQ)1 model and the Comprehensive Air Quality Model with Extensions (CAMx)2 have long been used to develop air quality management strategies aimed at reducing emissions of precursor species (nitrogen oxides and volatile organic compounds) for areas exceeding the ozone NAAQS. As the NAAQS became more stringent, processes considered in AQM were expanded from representing photochemistry causing elevated ozone levels in highly polluted urban airsheds such as the Los Angeles basin to also considering regional aspects such as the multi-state transport of ozone and its precursors and the effects of long-range international transport.
Long-term monitoring of ambient air quality and deposition is necessary to characterize trends in human and ecosystem exposure and to gauge the effectiveness of air pollution control programs. Such datasets are rare because of the difficulty and capital required to consistently and accurately collect and analyze samples over time from a spatially adequate number of regionally representative sites. Most of the national air pollutant monitoring networks producing these datasets were established in the 1970s and 1980s and focused on the human health-based National Ambient Air Quality Standards (NAAQS) criteria pollutants (e.g. sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), particulate matter < 2.5 μm (PM2.5)) or reporting acid rain trends and visibility impairment.
Models that accurately predict atmospheric composition and correctly respond to tested policy scenarios aid air quality managers in the development of effective strategies to protect human health. Controllable emissions from human activity interact with natural emissions from plants and trees from the biosphere through complex chemistry to form ozone (O3) and organic fine particulate matter (PM2.5), criteria air pollutants that induce a variety of adverse health effects. While organic gases emitted from plants and trees are natural, some fraction of the subsequent O3 and PM2.5 is not. Accurate assessment of the extent to which human activity and natural emissions interact to form pollution can be achieved when models are constructed from first principle chemical and physical laws, and tested and evaluated with laboratory and field observations. In the summer of 2013, hundreds of scientists descended on the southeast U.S. to coordinate an atmospheric chemistry campaign with the ultimate goal of understanding complex biosphere-atmosphere interactions, the subsequent formation of O3 and PM2.5, and accurate incorporation of the chemistry into atmospheric models. A main finding from the campaign is that anthropogenic emissions facilitate formation of organic PM2.5 derived from biogenic VOCs. This fraction of PM2.5 is controllable pollution. Mechanistic insight from that campaign was recently incorporated into EPA's air quality model, improving the model representation of the atmospheric modeling and informing air quality management strategies for PM2.5. Emission reductions in SO2 and NOx in the southeast U.S. are found to reduce non-fossil, presumably biogenic, organic PM2.5 mass concentrations, suggesting existing Federal rules have been more successful than anticipated. Additional potential feedback mechanisms may become important as emissions reductions bring the atmosphere into new chemical regimes.
Atmospheric deposition, both wet and dry, can be an important contributor to nitrogen and sulfur loading to ecosystems. Excessive deposition can cause acidification and eutrophication which can lead to harmful effects such as algal blooms, decreases in forest growth, loss of species richness, and shifts in species distribution. In more moderate amounts, atmospheric deposition can be a source of nutrients reducing the need for fertilization of agricultural areas. Quantifying the amount of atmospheric deposition is therefore a critical activity for both the US and Canada.
s are being solicited on the following topics: AERMOD • Long-range Transport Modeling • Modeling of Secondary Pollutant Formation, PM2.5, and Ozone • Background Concentrations • Meteorological Data Issues • Wind Tunnel and Computational Fluid Dynamics • and Revisions of the Guideline and Regulatory Application of Models. Please see the website at www.awma.org/aqmodels for complete submittal details. Abstracts due October 15, 2018. Air Quality Measurement Methods and Technology April 2-4, 2019 • Sheraton Imperial Hotel, Raleigh-Durham Airport Explore advances in measurement technology, data quality assurance, and data uses at this popular specialty conference covering air quality issues related to emerging pollutants, stationary source compliance, ambient monitoring, fugitive and area source air emissions, and quality assurance, and how they can be used to improve models, emission inventories, and policy decisions. Suggested topics: Ambient Air Monitoring • Coarse and Fine Particulate Matter • Stationary Sources • Data Quality • Mobile Monitoring Platforms • Optical and Optical Remote Monitoring • Low-cost Sensors • Passive Measurements and Fence Line Monitoring • Air Toxics Measurement Methods • Continuous HAP Monitoring, and more. Abstracts are due October 22, 2018. Find complete details online at www.awma.org/measurements.s are due October 22, 2018. Find complete details online at www.awma.org/measurements. Share your work, advance the industry, learn the latest, and make new connections.
The CMAQ model (Version 5.2) contains a lightning NOx algorithm that uses observed lightning flashes along with an assumed NOx production per flash and a scheme to distribute the NOx in the vertical atmosphere. A CMAQ simulation for summer 2011 shows that the LNOx to total NOx emission ratio are highest in the Southeast and Rocky Mountains regions. The addition of lightning NOx emissions reduces the daily CMAQ low bias for maximum 8-hr O3 by as much as 5 ppbv in the Rocky Mountains region. The lightning source of NOx should be included in regional air quality models.
