7 research outputs found
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 C<sub>2</sub>H<sub>6</sub> (rather than CO), effecting
a series of reactions that ultimately produces 25 molecules of NO<sub>2</sub> 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 C<sub>3</sub>H<sub>6</sub>O 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 C<sub>3</sub>H<sub>4</sub> (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 (NO<sub>2</sub>), 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<sub><i>x</i></sub>) 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 NO<sub>2</sub> 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 NO<sub>2</sub> and BC emissions. Emission rates for
NO<sub>2</sub> 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 (HOCH<sub>2</sub>CH<sub>2</sub>OH), 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