Use of an Unmanned Aircraft System to Quantify NO_x Emissions from a Natural Gas Boiler

Aerial emission sampling of four natural gas boiler stack plumes was conducted using an unmanned aerial system (UAS) equipped with a light-weight sensor/sampling system (the “Kolibri”) for measurement of nitrogen oxide (NO), and nitrogen dioxide (NO2), carbon dioxide (CO2), and carbon monoxide (CO). Flights (n = 22) ranged from 11 to 24 minutes duration at two different sites. The UAS was maneuvered into the plumes with the aid of real-time CO2 telemetry to the ground operators and, at one location, a second UAS equipped with an infrared/visible camera. Concentrations were collected and recorded at 1 Hz. The maximum CO2, CO, NO, and NO2 concentrations in the plume measured were 10,000 ppm, 7 ppm, 27 ppm, and 1.5 ppm, respectively. Comparison of the NOx emissions between the stack continuous emission monitoring systems and the UAS/Kolibri for three boiler sets showed an average of 5.6 % and 3.5 % relative percent difference for the run-weighted and carbon-weighted average emissions, respectively.

An assessment of the performance of the Monitor for AeRosols and GAses in ambient air (MARGA): a semi-continuous method for soluble compounds

Ambient air monitoring as part of the US Environmental Protection Agency's (US EPA's) Clean Air Status and Trends Network (CASTNet) currently uses filter packs to measure weekly integrated concentrations. The US EPA is interested in supplementing CASTNet with semi-continuous monitoring systems at select sites to characterize atmospheric chemistry and deposition of nitrogen and sulfur compounds at higher time resolution than the filter pack. The Monitor for AeRosols and GAses in ambient air (MARGA) measures water-soluble gases and aerosols at hourly temporal resolution. The performance of the MARGA was assessed under the US EPA Environmental Technology Verification (ETV) program. The assessment was conducted in Research Triangle Park, North Carolina from 8 September–8 October 2010 and focused on gaseous SO2, HNO3 and NH3 and aerosol SO4−, NO3− and NH4+. Precision of the MARGA was evaluated by calculating the median absolute relative percent difference (MARPD) between paired hourly results from duplicate MARGA units (MUs), with a performance goal of <25%. The accuracy of the MARGA was evaluated by calculating the median absolute relative percent difference (MARPD) for each MU relative to the average of the duplicate denuder/filter pack concentrations, with a performance goal of ≤40%. Accuracy was also evaluated by using linear regression, where MU concentrations were plotted against the average of the duplicate denuder/filter pack concentrations. From this, a linear least squares line of best fit was applied. The goal was for the slope of the line of best fit to be between 0.8 and 1.2. The MARGA performed well in comparison to the denuder/filter pack for SO2, SO42− and NH4+, with all three compounds passing the accuracy and precision goals by a significant margin. The performance of the MARGA in measuring NO3− could not be evaluated due to the different sampling efficiency of coarse NO3− by the MUs and the filter pack. Estimates of "fine" NO3− were calculated for the MUs and the filter pack. Using this and results from a previous study, it is concluded that if the MUs and the filter pack were sampling the same particle size, the MUs would have good agreement in terms of precision and accuracy. The MARGA performed moderately well in measuring HNO3 and NH3, though neither met the linear regression slope goals. However, recommendations for improving the measurement of HNO3 and NH3 are discussed. It is concluded that SO42−, SO2, NO3−, HNO3, NH4+ and NH3 concentrations can be measured with acceptable accuracy and precision when the MARGA is operated in conjunction with the recommendations outlined in the manuscript.

Refinement of the λ/2 contribution to CCD detector data

A new method is proposed to improve structure modeling by taking into account the half-wavelength contribution (λ/2) to X-ray data measured on CCD and image-plate diffractometers. Such an effect arises because the reflection intensities contain contributions associated with both the λ and the λ/2 wavelengths. The ratiowof these two contributions is a new parameter refined using the full-matrix least-squares techniques. The new method does not require any additional measurement or information. According to the tests performed, proper account of the λ/2 contribution lowers thewR2(|F|2) factors by a relative percent difference of 4–14% and the atomic displacement parameters by ∼1–4 s.u. Other effects are analyzed that might correlate with the λ/2 contribution, such as absorption, charge-density redistribution, thermal diffuse scattering and extinction. Strong correlation was found betweenwand the other parameters, but a fixed λ/2 correction reduces this difficulty. The value ofwis found to be both characteristic of the diffractometer and a general indicator of the refinement quality (similar toRfactors).