On-Road Ammonia Emissions Characterized by Mobile, Open-Path Measurements

Ammonia (NH₃) is a key precursor species to atmospheric fine particulate matter with strong implications for regional air quality and global climate change. NH₃ from vehicles accounts for a significant fraction of total emissions of NH₃ in urban areas. A mobile platform is developed to measure NH₃, CO, and CO₂ from the top of a passenger car. The mobile platform conducted 87 h of on-road measurements, covering 4500 km in New Jersey and California. The average on-road emission factor (EF) in CA is 0.49 ± 0.06 g NH₃ per kg fuel and agrees with previous studies in CA (0.3–0.8 g/kg). The mean on-road NH₃:CO emission ratio is 0.029 ± 0.005, and there is no systematic difference between NJ and CA. On-road NH₃ EFs increase with road gradient by an enhancement of 53 mg/kg fuel per percentage of gradient. On-road NH₃ EFs show higher values in both stop-and-go driving conditions and freeway speeds with a minimum near 70 km/h. Consistent with prior studies, the on-road emission ratios suggest a highly skewed distribution of NH₃ emitters. Comparisons with existing NJ and CA on-road emission inventories indicate that there may be an underestimation of on-road NH₃ emissions in both NJ and CA. We demonstrate that mobile, open-path measurements provide a unique tool to help quantitatively understand the on-road NH₃ emissions in urban and suburban settings

Effluent Gas Flux Characterization during Pyrolysis of Chicken Manure

Pyrolysis is a viable option for the production of renewable energy and agricultural resources from diverted organic waste streams. This high temperature thermochemical process yields material with beneficial reuses, including bio-oil and biochar. Gaseous forms of carbon (C) and nitrogen (N) are also emitted during pyrolysis. The effluent mass emission rates from pyrolysis are not well characterized, thus limiting proper evaluation of the environmental benefits or costs of pyrolysis products. We present the first comprehensive suite of C and N mass emission rate measurements of a biomass pyrolysis process that uses chicken manure as the feedstock to produce biochar and bio-oil. Two chicken manure fast pyrolysis experiments were conducted at controlled temperature ranges of 450–485 °C and 550–585 °C. Mass emission rates of nitrous oxide (N₂O), nitric oxide (NO), carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), and ammonia (NH₃) were measured using trace gas analyzers. Based on the system mass balance, 23–25% of the total mass of the manure feedstock was emitted as gas, while 52–55% and 23% were converted to bio-oil and biochar, respectively. CO₂ and NH₃ were the dominant gaseous species by mass, accounting for 58–65% of total C mass emitted and 99% of total reactive N mass emitted, respectively. Temperature variations within the two set of temperature ranges had a perfunctory effect on bio-oil production and gaseous emissions, but the higher temperature range process produced more bio-oil and slightly less emissions. However, a larger effect on the relative amounts of CO and CO₂ produced were observed between the different temperature regimes. These results have important implications for greenhouse gas and reactive N life cycle assessments of biochar and bio-oil

Near-Field Characterization of Methane Emission Variability from a Compressor Station Using a Model Aircraft

A model aircraft equipped with a custom laser-based, open-path methane sensor was deployed around a natural gas compressor station to quantify the methane leak rate and its variability at a compressor station in the Barnett Shale. The open-path, laser-based sensor provides fast (10 Hz) and precise (0.1 ppmv) measurements of methane in a compact package while the remote control aircraft provides nimble and safe operation around a local source. Emission rates were measured from 22 flights over a one-week period. Mean emission rates of 14 ± 8 g CH₄ s^–1 (7.4 ± 4.2 g CH₄ s^–1 median) from the station were observed or approximately 0.02% of the station throughput. Significant variability in emission rates (0.3–73 g CH₄ s^–1 range) was observed on time scales of hours to days, and plumes showed high spatial variability in the horizontal and vertical dimensions. Given the high spatiotemporal variability of emissions, individual measurements taken over short durations and from ground-based platforms should be used with caution when examining compressor station emissions. More generally, our results demonstrate the unique advantages and challenges of platforms like small unmanned aerial vehicles for quantifying local emission sources to the atmosphere

Vehicle Emissions as an Important Urban Ammonia Source in the United States and China

Ammoniated aerosols are important for urban air quality, but emissions of the key precursor NH₃ are not well quantified. Mobile laboratory observations are used to characterize fleet-integrated NH₃ emissions in six cities in the U.S. and China. Vehicle NH₃:CO₂ emission ratios in the U.S. are similar between cities (0.33–0.40 ppbv/ppmv, 15% uncertainty) despite differences in fleet composition, climate, and fuel composition. While Beijing, China has a comparable emission ratio (0.36 ppbv/ppmv) to the U.S. cities, less developed Chinese cities show higher emission ratios (0.44 and 0.55 ppbv/ppmv). If the vehicle CO₂ inventories are accurate, NH₃ emissions from U.S. vehicles (0.26 ± 0.07 Tg/yr) are more than twice those of the National Emission Inventory (0.12 Tg/yr), while Chinese NH₃ vehicle emissions (0.09 ± 0.02 Tg/yr) are similar to a bottom-up inventory. Vehicle NH₃ emissions are greater than agricultural emissions in counties containing near half of the U.S. population and require reconsideration in urban air quality models due to their colocation with other aerosol precursors and the uncertainties regarding NH₃ losses from upwind agricultural sources. Ammonia emissions in developing cities are especially important because of their high emission ratios and rapid motorizations