Search for: All records

The first 5 hours of aging in biomass burning plumes can strongly affect ozone photochemistry. We examine how volatile organic compounds (VOCs), nitrogen oxides, and nitrous acid influence hydroxyl radical, ozone, and peroxyacetyl nitrate (PAN) based on three aircraft campaigns over the United States. Our analyses reveal variable, highly elevated hydroxyl radical concentrations in the first 2 hours, resulting in evident fire-to-fire variability in VOCs oxidation and in ozone and PAN production. About 40 to 70% of the variability is explained by chemical aging. Ozone production in the plumes is usually VOC-limited for the first 2 hours and then nitrogen oxide limited downwind. Box model results for hydroxyl radical, ozone, and most VOCs, using the full, explicit Master Chemical Mechanism (MCM) mechanism, suggest no major gaps in the current best knowledge of gas-phase chemistry. However, the MCM sometimes overestimates PAN due to underestimated nitrogen oxide sinks. GEOS-Chem, a widely used chemical transport model with a reduced mechanism, generally underperforms because of incomplete VOC representation. We identify these critical pathways to guide future model development. 

The geosciences have the lowest racial and ethnic diversity of all STEM fields at all levels of higher education, and atmospheric science is emblematic of this discrepancy. Despite a growing awareness of the problem, Black, Indigenous, people of color, persons with disabilities, women, and LGBTQIA+ persons continue to be largely absent in academic programs and in the geoscience workforce. There is a desire and need for new approaches, new entry points, and higher levels of engagement to foster a diverse community of researchers, scholars, and practitioners in atmospheric science. One challenge among many is that diversity, equity, and inclusion efforts are often siloed from many aspects of the scientific process, technical training, and scientific community. We have worked toward bridging this gap through the development of a new atmospheric science course designed to break down traditional barriers for entry into diversity, equity, and inclusion engagement by graduate students, so they emerge better prepared to address issues of participation, representation, and inclusion. This article provides an overview of our new course, focused on social responsibility in atmospheric science. This course was piloted during Fall 2021 with the primary objective to educate and empower graduate students to be “diversity champions” in our field. We describe 1) the rationale for a course of this nature within a graduate program, 2) course design and content, 3) service-learning projects, 4) impact of the course on students, and 5) scalability to other atmospheric science graduate programs. 

Abstract Ammonia (NH₃) from animal feeding operations (AFOs) is an important source of reactive nitrogen in the US, but despite its ramifications for air quality and ecosystem health, its near‐source evolution remains understudied. To this end, Phase I of the Transport and Transformation of Ammonia (TRANS²Am) field campaign was conducted in the northeastern Colorado Front Range in summer 2021 and characterized atmospheric composition downwind of AFOs during 10 research flights. Airborne measurements of NH₃, nitric acid (HNO₃), and a suite of water‐soluble aerosol species collected onboard the University of Wyoming King Air research aircraft present an opportunity to investigate the sensitivity of particulate matter (PM) formation to AFO emissions. We couple the observations with thermodynamic modeling to predict the seasonality of ammonium nitrate (NH₄NO₃) formation. We find that during TRANS²Am northeastern Colorado is consistently in the NH₃‐rich and HNO₃‐limited NH₄NO₃formation regime. Further investigation using the Extended Aerosol Inorganics Model reveals that summertime temperatures (mean: 23°C) of northeastern Colorado, especially near the surface, inhibit NH₄NO₃formation despite high NH₃concentrations (max: ≤114 ppbv). Finally, we model spring/autumn and winter conditions to explore the seasonality of NH₄NO₃formation and find that cooler temperatures could support substantially more NH₄NO₃formation. Whereas NH₄NO₃only exceeds 1 μg m⁻³∼10% of the time in summer, modeled NH₄NO₃would exceed 1 μg m⁻³61% (88%) of the time in spring/autumn (winter), with a 10°C (20°C) temperature decrease relative to the campaign. 

Abstract. Agricultural emissions, including those from concentrated animal feeding operations (CAFOs) for beef and dairy cattle, make up a large portion of the United States' total greenhouse gas (GHG) emissions. However, many CAFOs reside in areas where methane (CH4) from oil and natural gas (ONG) complicates the quantification of CAFO emissions. Traditional approaches to quantify emissions in such regions often relied on inventory subtraction of other known sources. We compare the results of two approaches to attribute the CAFO CH4 emission rate from the total CH4 emission rate derived from an aircraft mass balance technique. These methods make use of the mixing ratio data of CH4, ethane (C2H6), and ammonia (NH3) that were collected simultaneously in-flight downwind of CAFOs in northeastern Colorado. The first approach, the subtraction method (SM), is similar to inventory subtraction, except the amount to be removed is derived from the observed C2H6 to CH4 ratio rather than an inventory estimate. The results from this approach showed high uncertainty, primarily due to how error propagates through subtraction. Alternatively, multivariate regression (MVR) can be used to estimate CAFO CH4 emissions using the NH3 emission rate and an NH3 to CH4 ratio. These results showed significantly less uncertainty. We identified criteria to determine the best attribution method; these criteria can support attribution in other regions. The final emission estimates for the CAFOs presented here were 13 ± 3 g of CH4 per head per hour and 13 ± 2 g of NH3 per head per hour. These estimates are higher than the inventory of the US Environmental Protection Agency (EPA) and previous studies highlighting the need for more measurements of CH4 and NH3 emission rates. 

Abstract Phase One of the Transportation and Transformation of Ammonia (TRANS²Am) field campaign took place in northeastern Colorado during the summer of 2021. One of the goals of TRANS²Am was to measure ammonia (NH₃) emissions from cattle feedlots and dairies. Most of these animal husbandry facilities are co‐located within oil and gas development, an important source of methane (CH₄) and ethane (C₂H₆) in the region. Phase One of TRANS²Am included 12 near‐source research flights. We present estimates of NH₃emissions ratios with respect to CH₄(NH₃EmR), with and without correction of CH₄from oil and gas, for 29 feedlots and dairies in the region. The data shows larger emissions ratios than previously reported in the literature with a large range of values (i.e., 0.1–2.6 ppbv ppbv⁻¹). Facilities housing cattle and dairy had a mean (std) of 1.20 (0.63) and 0.29 (0.08) ppbv ppbv⁻¹, respectively. We also found that only 15% of the total ammonia (NH_x) is in the particle phase (i.e., ) near major sources during the warm summertime months. We examined the evolution of NH₃in one plume that was sampled at different distances and altitudes up to 25 km downwind and estimated the NH₃lifetime against deposition and partitioning to the particle phase to be 87–120 min. Finally, we calculated estimates of NH₃emission rates from four optimally sampled facilities. These ranged from 4 to 29 g NH₃ · h⁻¹ · hd⁻¹. 

Key Points Smoke is most prevalent in the atmospheric column over the United States in the mid to late growing season months of July and August Smoke‐induced increases in the average diffuse fraction (DF) of surface‐level photosynthetically active radiation are greatest on clear‐sky days Ground and satellite observations show that DF increases and total irradiance decreases with increasing smoke optical depth