Ethane-Based Chemical Amplification Measurement Technique for Atmospheric Peroxy Radicals

Peroxy radicals play important roles in the atmospheric oxidation of organic compounds and the formation of ozone and secondary organic aerosol. There are few peroxy radical measurement techniques; the most common, chemical amplification using CO and NO, requires the use of toxic reagents, and its calibration factor is very sensitive to relative humidity. We present a new method for quantifying atmospheric peroxy radicals, ECHAMP (Ethane CHemical AMPlifier). Sampled air is mixed with NO and C₂H₆ (rather than CO), effecting a series of reactions that ultimately produces 25 molecules of NO₂ per sampled peroxy radical under dry conditions. This “amplification” factor decreases to 17 at a relative humidity of 50%, yielding a 1σ precision for 90 s average measurements of 0.8–2.5 ppt depending on the atmospheric variability of ozone. We demonstrated the utility of the new technique with measurements in Bloomington, IN, in July 2015

Direct measurement of volatile organic compound emissions from industrial flares using real-time online techniques: Proton Transfer Reaction Mass Spectrometry and Tunable Infrared Laser Differential Absorption Spectroscopy

During the 2010 Comprehensive Flare Study a suite of analytical instrumentation was employed to monitor and quantify in real-time the volatile organic compound (VOC) emissions emanating from an industrial chemical process flare burning either propene/natural gas or propane/natural gas. To our knowledge this represents the first time the VOC composition has been directly measured as a function of flare efficiency on an operational full-scale flare. This compositional information was obtained using a suite of proton-transfer-reaction mass spectrometers (PTR-MS) and quantum cascade laser tunable infrared differential absorption spectrometers (QCL-TILDAS) to measure the unburned fuel and associated combustion byproducts. Methane, ethyne, ethene, and formaldehyde were measured using the QC-TILDAS. Propene, acetaldehyde, methanol, benzene, acrolein, and the sum of the C₃H₆O isomers were measured with the PTR-MS. A second PTR-MS equipped with a gas chromatograph (GC) was operated in parallel and was used to verify the identity of the neutral components that were responsible for producing the ions monitored with the first PTR-MS. Additional components including 1,3-butadiene and C₃H₄ (propyne or allene) were identified using the GC/PTR-MS. The propene concentrations derived from the PTR-MS were found to agree with measurements made using a conventional GC with a flame ionization detector (FID). The VOC product (excludes fuel components) speciation profile is more dependent on fuel composition, propene versus propane, than on flare type, air-assisted versus steam-assisted, and is essentially constant with respect to combustion efficiency for combustion efficiencies >0.8. Propane flares produce more alkenes with ethene and propene accounting for approximately 80% (per carbon basis) of the VOC combustion product. The propene partial combustion product profile was observed to contain relatively more oxygenated material where formaldehyde and acetaldehyde are major contributors and account for ∼20 - 25% of VOC product carbon. Steam-assisted flares produce less ethyne and benzene than air-assisted flares. This observation is consistent with the understanding that steam assisted flares are more efficient at reducing soot, which is formed via the same reaction mechanisms that form benzene and ethyne

On-Road Measurement of Gas and Particle Phase Pollutant Emission Factors for Individual Heavy-Duty Diesel Trucks

Pollutant concentrations in the exhaust plumes of individual diesel trucks were measured at high time resolution in a highway tunnel in Oakland, CA, during July 2010. Emission factors for individual trucks were calculated using a carbon balance method, in which pollutants measured in each exhaust plume were normalized to measured concentrations of carbon dioxide. Pollutants considered here include nitric oxide, nitrogen dioxide (NO₂), carbon monoxide, formaldehyde, ethene, and black carbon (BC), as well as optical properties of emitted particles. Fleet-average emission factors for oxides of nitrogen (NO_<i>x</i>) and BC respectively decreased 30 ± 6 and 37 ± 10% relative to levels measured at the same location in 2006, whereas a 34 ± 18% increase in the average NO₂ emission factor was observed. Emissions distributions for all species were skewed with a small fraction of trucks contributing disproportionately to total emissions. For example, the dirtiest 10% of trucks emitted half of total NO₂ and BC emissions. Emission rates for NO₂ were found to be anticorrelated with all other species considered here, likely due to the use of catalyzed diesel particle filters to help control exhaust emissions. Absorption and scattering cross-section emission factors were used to calculate the aerosol single scattering albedo (SSA, at 532 nm) for individual truck exhaust plumes, which averaged 0.14 ± 0.03

Application of the Carbon Balance Method to Flare Emissions Characteristics

The destruction and removal efficiency (DRE) computation of target hydrocarbon species in the flaring process is derived using carbon balance methodologies. This analysis approach is applied to data acquired during the Texas Commission on Environmental Quality 2010 Flare Study. Example DRE calculations are described and discussed. Carbon balance is achieved to within 2% for the analysis of flare vent gases. Overall method uncertainty is evaluated and examined together with apparent variability in flare combustion performance. Using fast response direct sampling measurements to characterize flare combustion parameters is sufficiently accurate to produce performance curves on a large-scale industrial flare operating at low vent gas flow rates

Chemical Composition of Gas-Phase Organic Carbon Emissions from Motor Vehicles and Implications for Ozone Production

Motor vehicles are major sources of gas-phase organic carbon, which includes volatile organic compounds (VOCs) and other compounds with lower vapor pressures. These emissions react in the atmosphere, leading to the formation of ozone and secondary organic aerosol (SOA). With more chemical detail than previous studies, we report emission factors for over 230 compounds from gasoline and diesel vehicles via two methods. First we use speciated measurements of exhaust emissions from on-road vehicles in summer 2010. Second, we use a fuel composition-based approach to quantify uncombusted fuel components in exhaust using the emission factor for total uncombusted fuel in exhaust together with detailed chemical characterization of liquid fuel samples. There is good agreement between the two methods except for products of incomplete combustion, which are not present in uncombusted fuels and comprise 32 ± 2% of gasoline exhaust and 26 ± 1% of diesel exhaust by mass. We calculate and compare ozone production potentials of diesel exhaust, gasoline exhaust, and nontailpipe gasoline emissions. Per mass emitted, the gas-phase organic compounds in gasoline exhaust have the largest potential impact on ozone production with over half of the ozone formation due to products of incomplete combustion (e.g., alkenes and oxygenated VOCs). When combined with data on gasoline and diesel fuel sales in the U.S., these results indicate that gasoline sources are responsible for 69–96% of emissions and 79–97% of the ozone formation potential from gas-phase organic carbon emitted by motor vehicles

Combustion and Destruction/Removal Efficiencies of In-Use Chemical Flares in the Greater Houston Area

Alkene emissions from the petrochemical industry contribute significantly to ozone production in the greater Houston area but are underestimated in emission inventories. It is not well-known which processes (e.g., fugitive emissions, chemical flare emissions, etc.) are responsible for these underreported emissions. We use fast time response and ground-based mobile measurements of numerous trace gas species to characterize alkene plumes from three identified chemical flares in the greater Houston area. We calculate the combustion efficiency and destruction and removal efficiency (DRE) values of these flares using the carbon balance method. All three flares were operating at DRE values lower than required by regulation. An examination of photochemistry in flare exhaust plumes indicates that the impact of direct formaldehyde emissions from flares on ozone formation is small as compared to the impact of alkene emissions

Ethylene Glycol Emissions from On-road Vehicles

Ethylene glycol (HOCH₂CH₂OH), used as engine coolant for most on-road vehicles, is an intermediate volatility organic compound (IVOC) with a high Henry’s law coefficient. We present measurements of ethylene glycol (EG) vapor in the Caldecott Tunnel near San Francisco, using a proton transfer reaction mass spectrometer (PTR-MS). Ethylene glycol was detected at mass-to-charge ratio 45, usually interpreted as solely coming from acetaldehyde. EG concentrations in bore 1 of the Caldecott Tunnel, which has a 4% uphill grade, were characterized by infrequent (approximately once per day) events with concentrations exceeding 10 times the average concentration, likely from vehicles with malfunctioning engine coolant systems. Limited measurements in tunnels near Houston and Boston are not conclusive regarding the presence of EG in sampled air. Previous PTR-MS measurements in urban areas may have overestimated acetaldehyde concentrations at times due to this interference by ethylene glycol. Estimates of EG emission rates from the Caldecott Tunnel data are unrealistically high, suggesting that the Caldecott data are not representative of emissions on a national or global scale. EG emissions are potentially important because they can lead to the formation of secondary organic aerosol following oxidation in the atmospheric aqueous phase