Satellite-detected ammonia changes in the United States: Natural or anthropogenic impacts

Modeling ammonia emissions from manure in conventional, organic, and grazing dairy systems and practices to mitigate emissions

Almost 60% of all ammonia (NH3) emissions are from livestock manure. Understanding the sources and magnitude of NH3 emissions from manure systems is critical to implement mitigation strategies. This study models 13 archetypical conventional (5 farms), organic (5 farms), and grazing (3 farms) dairy farms to estimate NH3 emissions from manure at the barn, storage, and after land application. Mitigation practices related to management of the herd, crop production, and manure are subsequently modeled to quantify the change in NH3 emissions from manure by comparing archetypical practices with these alternative practices. A mass balance of nutrients is also conducted. Emissions per tonne of excreted manure for the manure system (barn, storage, and land application) range from 3.0 to 4.4 g of NH3 for conventional farms, 3.5 to 4.4 g of NH3 for organic farms, and 3.4 to 3.9 g of NH3 for grazing farms. For all farm types, storage and land application are the main sources of NH3 emissions from manure. In general, solid manures have higher emission intensities due to higher pH during storage (pH = 7.4 for liquid, 7.8 for slurry, and 8.5 for solid manure) and lower infiltration rates after land application when compared with slurry and liquid manures. The most effective management practices to reduce NH3 emissions from manure systems are combining solid-liquid separation with manure injection (up to 49% reduction in NH3 emissions), followed by injection alone, and reducing crude protein in the dairy ration, especially in organic and grazing farms that have grazing and forages as the main component of the dairy ration. This study also shows that the intensity of NH3 emissions from manure depends significantly on the functional unit and presents results per manure excreted, total solids in excreted manure, animal units, and fat- and protein-corrected milk.

Atmospheric ammonia in China: Long-term spatiotemporal variation, urban-rural gradient, and influencing factors

In recent years, atmospheric ammonia (NH₃) concentrations have increased in China. Ammonia control has become one of the next hot topics in air pollution mitigation with the increasing cost of acid gas emission reduction. In this study, using Infrared Atmospheric Sounding Interferometer (IASI) satellite observations, we analyzed the spatiotemporal distribution, the urban-rural gradient of the vertical column densities (VCDs) of NH₃ and the contribution of influencing factors (meteorology, social, atmospheric acid gases, and NH₃ emissions) in China from 2008 to 2019 using hotspot analysis, circular gradient analysis, geographical and temporal weighted regression, and some other methods. Our results showed that NH₃ VCDs in China have significantly increased (31.88 %) from 2008 to 2019, with the highest occurring in North China Plain. The average NH₃ VCDs in urban areas were significantly higher than those in rural areas, and the urban-rural gap in NH₃ VCDs was widening. The results of circular gradient analysis showed an overall decreasing trend in NH₃ VCDs along the urban-rural gradient. We used a geographically and temporally weighted regression model to analyze the contribution of various influencing factors to NH₃ VCDs: meteorology (30.13 %), social (27.40 %), atmospheric acid gases (23.20 %), and NH₃ emissions (19.28 %) factors. The results showed substantial spatiotemporal differences in the influencing factors. Atmospheric acid gas was the main reason for the increase in NH₃ VCDs from 2008 to 2019. A more thorough understanding of the spatiotemporal distribution, urban-rural variations, and factors influencing NH₃ in China will aid in developing control strategies to reduce PM_2.5.

Is the key-treatment-in-key-areas approach in air pollution control policy effective? Evidence from the action plan for air pollution prevention and control in China

The "Action Plan for Air Pollution Prevention and Control from 2013 to 2017" (APAPPC) establishes the key treatment for key areas in Beijing-Tianjin-Hebei and its surroundings (BTH), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD) in China. Is the key-treatment-in-key-areas approach effective? Except the targeted pollutants, does there exist the synergistic effects of other air pollutants? Are there differences between the north and the south about the effectiveness of this approach? To answer these new and key questions, this study uses the difference-in-difference (DID) model to evaluate whether it is more effective to implement key treatment policies for two targeted pollutants, PM_2.5 and PM_coarse (PM_2.5-PM₁₀), and verifies the synergistic emission-reduction effects of the policies on eight other emissions: SO₂, NO_X, VOC, CO, NH₃, BC, OC, and CO₂. At the same time, the policy effects are evaluated nationwide, in the north, and in the south using data from 2008 to 2017. The results show the following: (1) The APAPPC's establishment of the key treatment in key areas significantly reduces PM_2.5 and PM_coarse by 7.25 % and 10.49 %, respectively, compared with non-key areas nationwide. (2) The key-treatment-in-key-areas policy has synergistic effects on six other emissions: SO₂, NO_X, CO, BC, OC, and CO₂. (3) If viewing the north and the south separately, BTH beats other counterparts in the north by a large margin, while there is no significant difference among provinces and/or areas in the south. This margin is much larger than the one between key areas and other provinces nationwide. Therefore, this paper suggests that key treatment policies in key areas should continue to be implemented, especially for cities that have not dropped, but rather increased, their PM_2.5 concentrations. Additionally, air pollution goals should incorporate China's carbon peaking and neutrality goals to reduce air pollutants and greenhouse gas emissions.

Human Mobility to Parks Under the COVID-19 Pandemic and Wildfire Seasons in the Western and Central United States

In 2020, people's health suffered a great crisis under the dual effects of the COVID-19 pandemic and the extensive, severe wildfires in the western and central United States. Parks, including city, national, and cultural parks, offer a unique opportunity for people to maintain their recreation behaviors following the social distancing protocols during the pandemic. However, massive forest wildfires in western and central US, producing harmful toxic gases and smoke, pose significant threats to human health and affect their recreation behaviors and mobility to parks. In this study, we employed the geographically and temporally weighted regression (GTWR) Models to investigate how COVID-19 and wildfires jointly shaped human mobility to parks, regarding the number of visits per capita, dwell time, and travel distance to parks, during June - September 2020. We detected strong correlations between visitations and COVID-19 incidence in southern Montana, western Wyoming, Colorado, and Utah before August. However, the pattern was weakened over time, indicating the decreasing trend of the degree of concern regarding the pandemic. Moreover, more park visits and lower dwell time were found in parks further away from wildfires and less air pollution in Washington, Oregon, California, Colorado, and New Mexico, during the wildfire season, suggesting the potential avoidance of wildfires when visiting parks. This study provides important insights on people's responses in recreation and social behaviors when facing multiple severe crises that impact their health and wellbeing, which could support the preparation and mitigation of the health impacts from future pandemics and natural hazards.