Satellite-based aerosol optical depth estimates over the continental U.S. during the 2020 wildfire season: Roles of smoke and land cover.

Wildfires produce smoke that can affect an area >1000 times the burn extent, with far-reaching human health, ecologic, and economic impacts. Accurately estimating aerosol load within smoke plumes is therefore crucial for understanding and mitigating these impacts. We evaluated the effectiveness of the latest Collection 6.

Source characterization of volatile organic compounds at Carlsbad Caverns National Park.

Carlsbad Caverns National Park (CAVE), located in southeastern New Mexico, experiences elevated ground-level ozone (O) exceeding the National Ambient Air Quality Standard (NAAQS) of 70 ppbv. It is situated adjacent to the Permian Basin, one of the largest oil and gas (O&G) producing regions in the US. In 2019, the Carlsbad Caverns Air Quality Study (CarCavAQS) was conducted to examine impacts of different sources on ozone precursors, including nitrogen oxides (NO) and volatile organic compounds (VOCs).

Complexities in Modeling Organic Aerosol Light Absorption.

Aerosol particles dynamically evolve in the atmosphere by physicochemical interactions with sunlight, trace chemical species, and water. Current modeling approaches fix properties such as aerosol refractive index, introducing spatial and temporal errors in the radiative impacts. Further progress requires a process-level description of the refractive indices as the particles age and experience physicochemical transformations.

Wintertime haze and ozone at Dinosaur National Monument.

Dinosaur National Monument (DINO) is located near the northeastern edge of the Uinta Basin and often experiences elevated levels of wintertime ground-level ozone. Previous studies have shown that high ozone mixing ratios in the Uinta Basin are driven by elevated levels of volatile organic compounds (VOCs) and nitrogen oxides (NO) from regional oil and gas development coupled with temperature inversions and enhanced photochemistry from persistent snow cover. Here, we show that persistent snow cover and temperature inversions, along with abundant ammonia, also lead to wintertime haze in this region.

Ammonia Dry Deposition in an Alpine Ecosystem Traced to Agricultural Emission Hotpots.

Elevated reactive nitrogen (N) deposition is a concern for alpine ecosystems, and dry NH deposition is a key contributor. Understanding how emission hotspots impact downwind ecosystems through dry NH deposition provides opportunities for effective mitigation. However, direct NH flux measurements with sufficient temporal resolution to quantify such events are rare.

Persistent Nonagricultural and Periodic Agricultural Emissions Dominate Sources of Ammonia in Urban Beijing: Evidence from N Stable Isotope in Vertical Profiles.

Ammonia (NH) emission reduction is key to limiting the deadly PM pollution globally. However, studies of long-term source apportionment of vertical NH are relatively limited. On the basis of the one-year measurements of weekly vertical profiles of N-NH at 5 heights (2, 15, 102, 180, and 320 m) on a 325-m meteorological tower in urban Beijing, we found that vertical profiles of NH concentrations generally remained stable with height.

A review of measurements of air-surface exchange of reactive nitrogen in natural ecosystems across North America.

This review summarizes the state of the science of measurements of dry deposition of reactive nitrogen (Nr) compounds in North America, beginning with current understanding of the importance of dry deposition at the U.S. continental scale followed by a review of micrometeorological flux measurement methods.

Inorganic nitrogen wet deposition gradients in the Denver-Boulder metropolitan area and Colorado Front Range - Preliminary implications for Rocky Mountain National Park and interpolated deposition maps.

For the first time in the 40-year history of the National Atmospheric Deposition Program/National Trends Network (NADP/NTN), a unique urban-to-rural transect of wet deposition monitoring stations was operated as part of the NTN in 2017 to quantify reactive inorganic nitrogen wet deposition for adjacent urban and rural, montane regions. The transect of NADP stations (sites) was used to collect continuous precipitation depth and weekly wet-deposition samples in the Denver - Boulder, Colorado, urban corridor. Gradients in reactive inorganic nitrogen (Nr) concentrations and wet deposition were identified along the transect, which included Rocky Mountain National Park.

Impact of Front Range sources on reactive nitrogen concentrations and deposition in Rocky Mountain National Park.

Human influenced atmospheric reactive nitrogen (RN) is impacting ecosystems in Rocky Mountain National Park (ROMO). Due to ROMO's protected status as a Class 1 area, these changes are concerning, and improving our understanding of the contributions of different types of RN and their sources is important for reducing impacts in ROMO. In July-August 2014 the most comprehensive measurements (to date) of RN were made in ROMO during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ).

Quantum Yields of Nitrite (NO) from the Photolysis of Nitrate (NO) in Ice at 313 nm.

Photochemical reactions of nitrate in snow release reactive nitrogen species via two channels, which produce (1) nitrogen dioxide (NO) and hydroxyl radical (OH) and (2) nitrite (NO) and oxygen atom (O(P)). Quantum yields (Φ) for these channels are generally well characterized, except for channel 2 in ice. In this study, we quantify Φ(NO) in water ices and examine the impacts of pH and organic scavengers of OH.

Quantum Yield of Nitrite from the Photolysis of Aqueous Nitrate above 300 nm.

Photolysis of nitrate (NO) produces reactive nitrogen and oxygen species via three different channels, forming: (1) nitrogen dioxide (NO) and hydroxyl radical (OH), (2) nitrite (NO) and oxygen atom (O(P)), and (3) peroxynitrite (ONOO). These photoproducts are important oxidants and reactants in surface waters, atmospheric drops, and snowpacks. While the efficiency of the first channel, to form NO, is well documented, a large range of values have been reported for the second channel, nitrite, above 300 nm.

Aerosol species concentrations and source apportionment of ammonia at Rocky Mountain National Park.

Changes in ecosystem function at Rocky Mountain National Park (RMNP) are occurring because of emissions of nitrogen and sulfate species along the Front Range of the Colorado Rocky Mountains, as well as sources farther east and west. The nitrogen compounds include both oxidized and reduced nitrogen. A year-long monitoring program of various oxidized and reduced nitrogen species was initiated to better understand their origins as well as the complex chemistry occurring during transport from source to receptor.