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Critical Review

A&WMA's 117th Annual Conference & Exhibition: Emissions Reductions for Sustainable Energy Futures, June 24-27, 2024, Calgary, AB

The 54th Annual A&WMA Critical Review

Atmospheric Reduced Nitrogen: Sources, Transformations, Effects, and Management


Authors: Charles Driscoll, Syracuse University; Jana Milford and Daven Henze, University of Colorado; Michael Bell, U.S. National Park Service
 

Charles T. Driscoll Charles T. Driscoll, Lead Author and Presenter, University Professor of Environmental Systems and Distinguished Professor, Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY
 
Jana Milford Jana Milford, Professor Emerita of Mechanical Engineering, Department of Mechanical Engineering, University of Colorado, Boulder
Daven Henze Daven Henze, Associate Professor of Mechanical Engineering, Department of Mechanical Engineering, University of Colorado, Boulder
Michael Bell Michael Bell, Ecologist, U.S. National Park Service, Air Resources Division, Lakewood, CO

Nitrogen is an essential macronutrient in organisms and biotic processes, and commonly a growth limiting nutrient for primary producers in many terrestrial and marine ecosystems.   Over the past century, increased production of human-generated reactive nitrogen has greatly altered the global nitrogen cycle with diverse and profound benefits and many adverse health and environmental effects. Among these are a deterioration of air quality associated with emissions of nitrogen oxides, ammonia, and other forms of reduced nitrogen. In the 54th Annual A&WMA Critical Review, the authors examine current science on sources, processes, effects, and management of ammonia, focusing primarily on the United States with comparative insights from Europe and China.

 
Human activities emit ammonia into the atmosphere from vehicles, livestock, wastes, and fertilizer use. Concerns about perturbation of the nitrogen cycle and environmental consequences of ammonia emissions have been recognized for decades. In contrast to nitrogen oxides and other air pollutants of concern for which emissions have stabilized or declined over the past five decades, emissions of ammonia in the United States are increasing and projected to continue to increase in coming decades. In part, this ongoing pattern is because ammonia emissions, which derive mainly from the agricultural sector, are largely unregulated. Voluntary programs and U.S. Department of Agriculture incentives have had limited impact in mitigating emissions.
 
The critical review considers the processing and effects of ammonia on terrestrial and aquatic ecosystems and associated critical loads. Effects on human health, visibility, and climate are discussed. It covers recent developments in estimating emissions and modeling the contribution of ammonia to fine particulate matter and nitrogen deposition, including the use of satellite observations. The authors show that ongoing climate change and decreases in sulfur and nitrogen oxides emissions have implications for gas-particle partitioning and deposition patterns. Available methods to mitigate ammonia emissions and the history and status of emissions management efforts are described. The critical review concludes with recommendations for how the U.S. Environmental Protection Agency, other federal agencies, and states could enhance efforts to address ammonia emissions, and describes research needs to help design, implement, and track new efforts to mitigate emissions of ammonia.
 
The full-length paper will appear in the June 2024 issue of the Journal of the Air & Waste Management Association (JA&WMA) and its conclusions will be presented live as part of the 2024 A&WMA Annual Conference & Exhibition in Calgary, Alberta, Canada. Following the review presentation, a panel of invited experts will critique the presentation and offer their own views on the topic. Invited discussants will represent key stakeholder groups, including federal and state agencies; researchers; industry experts; NGOs; and community action groups. Comments also will be solicited from the floor during a live question-and-answer sequence to end the session. To complete the review process, the Critical Review Committee Chair will synthesize all of the discussion points into a single Discussion Paper that will be published in the October 2024 issue of JA&WMA.
About the Critical Review
For more than 50 years, A&WMA has solicited and published in the Journal of the Air & Waste Management Association (JA&WMA) an Annual Critical Review on a topic of critical importance to the air and waste management fields. Each year, the review author presents the Annual Critical Review during A&WMA’s Annual Conference & Exhibition. The Critical Review Committee, which is a subcommittee of the Publications Committee, selects the review topics, solicits the authors/presenters, offers editorial guidance and critiques to the review authors, reviews the final manuscript before publication, and selects the participants for the panel discussion that follows the review presentation. 

Complete list of past Critical Reviews
A&WMA Critical Review Committee Charter and Manual of Operations
A&WMA Critical Review Committee