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Concentrated animal feeding operations (CAFOs) are major emitters of both ammonia (NH3) and methane (CH4). However, current emission inventories have limited temporal resolution and use data derived from a small subset of farms. To this end, we deployed three mobile laboratories during the DISCOVER-AQ campaign in summer 2014 with a focus on northeastern Colorado. Observations of NH3 and CH4 plumes downwind of 43 CAFOs were used to investigate the diurnal and site-to-site variability of emissions with an inverse area source plume modeling approach. Ammonia emissions scaled to all permitted animals in Weld, Morgan, and Larimer counties were estimated at 1.9 Gg month-1, 50% greater than the U.S. NEI 2014 and 360% greater than EDGAR for the month of August. Methane emissions were likewise estimated at 10.6 Gg month-1, consistent with the U.S. GHGI but 99% greater than EDGAR. Significant differences between individual CAFOs with repeat observations were also observed for both CH4 and NH3 emissions. The large subfarm, site-to-site, and diurnal variabilities observed show the importance of measurements taken across these scales in order to derive representative emission factors.

Atmospheric emissions from animal husbandry are important to both air quality and climate, but are hard to characterize and quantify as they differ significantly due to management practices and livestock type, and they can vary substantially throughout diurnal and seasonal cycles. Using a new mobile laboratory, ammonia (NH3), methane (CH4), nitrous oxide (N2O), and other trace gas emissions were measured from four concentrated animal feeding operations (CAFOs) in northeastern Colorado. Two dairies, a beef cattle feedlot, and a sheep feedlot were chosen for repeated diurnal and seasonal measurements. A consistent diurnal pattern in the NH3 to CH4 enhancement ratio is clearly observed, with midday enhancement ratios approximately four times greater than nighttime values. This diurnal pattern is similar, with slight variations in magnitude, at the four CAFOs and across seasons. The average NH3 to CH4 enhancement ratio from all seasons and CAFOs studied is 0.17 (+0.13/–0.08) mol/mol, in agreement with statewi...

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.

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.