BTEX exposures in an area impacted by industrial and mobile sources: Source attribution and impact of averaging time

<p>The impacts of emissions plumes from major industrial sources on black carbon (BC) and BTEX (benzene, toluene, ethyl benzene, xylene isomers) exposures in communities located >10 km from the industrial source areas were identified with a combination of stationary measurements, source identification using positive matrix factorization (PMF), and dispersion modeling. The industrial emissions create multihour plume events of BC and BTEX at the measurement sites. PMF source apportionment, along with wind patterns, indicates that the observed pollutant plumes are the result of transport of industrial emissions under conditions of low boundary layer height. PMF indicates that industrial emissions contribute >50% of outdoor exposures of BC and BTEX species at the receptor sites. Dispersion modeling of BTEX emissions from known industrial sources predicts numerous overnight plumes and overall qualitative agreement with PMF analysis, but predicts industrial impacts at the measurement sites a factor of 10 lower than PMF. Nonetheless, exposures associated with pollutant plumes occur mostly at night, when residents are expected to be home but are perhaps unaware of the elevated exposure. Averaging data samples over long times typical of public health interventions (e.g., weekly or biweekly passive sampling) misapportions the exposure, reducing the impact of industrial plumes at the expense of traffic emissions, because the longer samples cannot resolve subdaily plumes. Suggestions are made for ways for future distributed pollutant mapping or intervention studies to incorporate high time resolution tools to better understand the potential impacts of industrial plumes.</p> <p><i>Implications</i>: Emissions from industrial or other stationary sources can dominate air toxics exposures in communities both near the source and in downwind areas in the form of multihour plume events. Common measurement strategies that use highly aggregated samples, such as weekly or biweekly averages, are insensitive to such plume events and can lead to significant under apportionment of exposures from these sources.</p

Secondary Organic Aerosol Formation from Intermediate-Volatility Organic Compounds: Cyclic, Linear, and Branched Alkanes

Intermediate volatility organic compounds (IVOCs) are an important class of secondary organic aerosol (SOA) precursors that have not been traditionally included in chemical transport models. A challenge is that the vast majority of IVOCs cannot be speciated using traditional gas chromatography-based techniques; instead they are classified as an unresolved complex mixture (UCM) that is presumably made up of a complex mixture of branched and cyclic alkanes. To better understand SOA formation from IVOCs, a series of smog chamber experiments was conducted with different alkanes, including cyclic, branched, and linear compounds. The experiments focused on freshly formed SOA from hydroxyl (OH) radical-initiated reactions under high-NO_<i>x</i> conditions at typical atmospheric organic aerosol concentrations (<i>C</i>_OA). SOA yields from cyclic alkanes were comparable to yields from linear alkanes three to four carbons larger in size. For alkanes with equivalent carbon numbers, branched alkanes had the lowest SOA mass yields, ranging between 0.05 and 0.08 at a <i>C</i>_OA of 15 μg m^–3. The SOA yield of branched alkanes also depends on the methyl branch position on the carbon backbone. High-resolution aerosol mass spectrometer data indicate that the SOA oxygen-to-carbon ratios were largely controlled by the carbon number of the precursor compound. Depending on the precursor size, the mass spectrum of SOA produced from IVOCs is similar to the semivolatile-oxygenated and hydrocarbon-like organic aerosol factors derived from ambient data. Using the new yield data, we estimated SOA formation potential from diesel exhaust and predict the contribution from UCM vapors to be nearly four times larger than the contribution from single-ring aromatics and comparable to that of polycyclic aromatic hydrocarbons after several hours of oxidation at typical atmospheric conditions. Therefore, SOA from IVOCs may be an important contributor to urban OA and should be included in SOA models; the yield data presented in this study are suitable for such use

Urban Organic Aerosol Exposure: Spatial Variations in Composition and Source Impacts

We conducted a mobile sampling campaign in a historically industrialized terrain (Pittsburgh, PA) targeting spatial heterogeneity of organic aerosol. Thirty-six sampling sites were chosen based on stratification of traffic, industrial source density, and elevation. We collected organic carbon (OC) on quartz filters, quantified different OC components with thermal-optical analysis, and grouped them based on volatility in decreasing order (OC1, OC2, OC3, OC4, and pyrolyzed carbon (PC)). We compared our ambient OC concentrations (both gas and particle phase) to similar measurements from vehicle dynamometer tests, cooking emissions, biomass burning emissions, and a highway traffic tunnel. OC2 and OC3 loading on ambient filters showed a strong correlation with primary emissions while OC4 and PC were more spatially homogeneous. While we tested our hypothesis of OC2 and OC3 as markers of fresh source exposure for Pittsburgh, the relationship seemed to hold at a national level. Land use regression (LUR) models were developed for the OC fractions, and models had an average <i>R</i>² of 0.64 (SD = 0.09). The paper demonstrates that OC2 and OC3 can be useful markers for fresh emissions, OC4 is a secondary OC indicator, and PC represents both biomass burning and secondary aerosol. People with higher OC exposure are likely inhaling more fresh OC2 and OC3, since secondary OC4 and PC varies much less drastically in space or with local primary sources

Characterizing the Spatial Variation of Air Pollutants and the Contributions of High Emitting Vehicles in Pittsburgh, PA

We used a mobile measurement platform to characterize a suite of air pollutants (black carbon (BC), particle-bound polycyclic aromatic hydrocarbons (PB–PAH), benzene, and toluene) in the city of Pittsburgh and surrounding areas. More than 270 h of data were collected from forty-two sites which were selected based on analysis in the geographic information system (GIS). Mobile measurements were performed during three different times of day (mornings, afternoons/evenings, and overnight) in both winter (November 2011 to February 2012) and summer (June 2012 to August 2012). Pollutant concentrations were elevated in river valleys by 9% (benzene) to 30% (PB–PAH) relative to upland areas. Traffic had strong impacts on measured pollutants. PB–PAH and BC concentrations at high traffic sites were a factor of 2 and 30% higher than at low traffic sites, respectively. Pollutant concentrations were highest in the morning sessions due to a combination of traffic and meteorological conditions. The highly time-resolved data indicated that elevated pollutant concentrations at high traffic sites were due to short duration plume events associated with high emitting vehicles. High emitting vehicles contributed up to 70% of the near road PB–PAH and 30% of BC; emissions from these vehicles drove substantial spatial variations in BC and PB–PAH concentrations. Many high emitting vehicles were presumably diesel trucks or buses, because plumes were strongly correlated with truck traffic volume. In contrast, PB–PAH and BC in the nonplume background air was weakly correlated with traffic, and their spatial patterns were more influenced by terrain and point source emissions. The spatial variability in contributions of high emitting vehicles suggests that the effect of potential control strategies vary for different pollutants and environments

Estimating ambient particulate organic carbon concentrations and partitioning using thermal optical measurements and the volatility basis set

<p>We introduce a new method to estimate the mass concentration of particulate organic carbon (POC) collected on quartz filters, demonstrating it using quartz-filter samples collected in greater Pittsburgh. This method combines thermal-optical organic carbon and elemental carbon (OC/EC) analysis and the volatility basis set (VBS) to quantify the mass concentration of semi-volatile POC on the filters. The dataset includes ambient samples collected at a number of sites in both summer and winter as well as samples from a highway tunnel. As a reference we use the two-filter bare-Quartz minus Quartz-Behind-Teflon (Q-QBT) approach to estimate the adsorbed gaseous fraction of organic carbon (OC), finding a substantial fraction in both the gas and particle phases under all conditions. In the new method we use OC fractions measured during different temperature stages of the OC/EC analysis for the single bare-quartz (BQ) filter in combination with partitioning theory to predict the volatility distributions of the measured OC, which we describe with the VBS. The effective volatility bins are consistent for data from both ambient samples and primary organic aerosol (POA)-enriched tunnel samples. Consequently, with the VBS model and total OC fractions measured over different heating stages, particulate OC can be determined by using the BQ filter alone. This method can thus be applied to all quartz filter-based OC/EC analyses to estimate the POC concentration without using backup filters.</p> <p>© 2016 American Association for Aerosol Research</p

Methane Emissions from Conventional and Unconventional Natural Gas Production Sites in the Marcellus Shale Basin

There is a need for continued assessment of methane (CH₄) emissions associated with natural gas (NG) production, especially as recent advancements in horizontal drilling combined with staged hydraulic fracturing technologies have dramatically increased NG production (we refer to these wells as “unconventional” NG wells). In this study, we measured facility-level CH₄ emissions rates from the NG production sector in the Marcellus region, and compared CH₄ emissions between unconventional NG (UNG) well pad sites and the relatively smaller and older “conventional” NG (C_<i>v</i>NG) sites that consist of wells drilled vertically into permeable geologic formations. A top-down tracer-flux CH₄ measurement approach utilizing mobile downwind intercepts of CH₄, ethane, and tracer (nitrous oxide and acetylene) plumes was performed at 18 C_<i>v</i>NG sites (19 individual wells) and 17 UNG sites (88 individual wells). The 17 UNG sites included four sites undergoing completion flowback (FB). The mean facility-level CH₄ emission rate among UNG well pad sites in routine production (18.8 kg/h (95% confidence interval (CI) on the mean of 12.026.8 kg/h)) was 23 times greater than the mean CH₄ emissions from C_<i>v</i>NG sites. These differences were attributed, in part, to the large size (based on number of wells and ancillary NG production equipment) and the significantly higher production rate of UNG sites. However, C_<i>v</i>NG sites generally had much higher production-normalized CH₄ emission rates (median: 11%; range: 0.3591%) compared to UNG sites (median: 0.13%, range: 0.011.2%), likely resulting from a greater prevalence of avoidable process operating conditions (e.g., unresolved equipment maintenance issues). At the regional scale, we estimate that total annual CH₄ emissions from 88 500 combined C_<i>v</i>NG well pads in Pennsylvania and West Virginia (660 Gg (95% CI: 500 to 800 Gg)) exceeded that from 3390 UNG well pads by 170 Gg, reflecting the large number of C_<i>v</i>NG wells and the comparably large fraction of CH₄ lost per unit production. The new emissions data suggest that the recently instituted Pennsylvania CH₄ emissions inventory substantially underestimates measured facility-level CH₄ emissions by >1040 times for five UNG sites in this study

Gas-Particle Partitioning of Primary Organic Aerosol Emissions: (2) Diesel Vehicles

Experiments were performed to investigate the gas-particle partitioning of primary organic aerosol (POA) emissions from two medium-duty (MDDV) and three heavy-duty (HDDV) diesel vehicles. Each test was conducted on a chassis dynamometer with the entire exhaust sampled into a constant volume sampler (CVS). The vehicles were operated over a range of driving cycles (transient, high-speed, creep/idle) on different ultralow sulfur diesel fuels with varying aromatic content. Four independent yet complementary approaches were used to investigate POA gas-particle partitioning: artifact correction of quartz filter samples, dilution from the CVS into a portable environmental chamber, heating in a thermodenuder, and thermal desorption/gas chromatography/mass spectrometry (TD-GC-MS) analysis of quartz filter samples. During tests of vehicles not equipped with diesel particulate filters (DPF), POA concentrations inside the CVS were a factor of 10 greater than ambient levels, which created large and systematic partitioning biases in the emissions data. For low-emitting DPF-equipped vehicles, as much as 90% of the POA collected on a quartz filter from the CVS were adsorbed vapors. Although the POA emission factors varied by more than an order of magnitude across the set of test vehicles, the measured gas-particle partitioning of all emissions can be predicted using a single volatility distribution derived from TD-GC-MS analysis of quartz filters. This distribution is designed to be applied directly to quartz filter data that are the basis for existing emissions inventories and chemical transport models that have implemented the volatility basis set approach

Fuel Composition and Secondary Organic Aerosol Formation: Gas-Turbine Exhaust and Alternative Aviation Fuels

A series of smog chamber experiments were performed to investigate the effects of fuel composition on secondary particulate matter (PM) formation from dilute exhaust from a T63 gas-turbine engine. Tests were performed at idle and cruise loads with the engine fueled on conventional military jet fuel (JP-8), Fischer–Tropsch synthetic jet fuel (FT), and a 50/50 blend of the two fuels. Emissions were sampled into a portable smog chamber and exposed to sunlight or artificial UV light to initiate photo-oxidation. Similar to previous studies, neat FT fuel and a 50/50 FT/JP-8 blend reduced the primary particulate matter emissions compared to neat JP-8. After only one hour of photo-oxidation at typical atmospheric OH levels, the secondary PM production in dilute exhaust exceeded primary PM emissions, except when operating the engine at high load on FT fuel. Therefore, accounting for secondary PM production should be considered when assessing the contribution of gas-turbine engine emissions to ambient PM levels. FT fuel substantially reduced secondary PM formation in dilute exhaust compared to neat JP-8 at both idle and cruise loads. At idle load, the secondary PM formation was reduced by a factor of 20 with the use of neat FT fuel, and a factor of 2 with the use of the blend fuel. At cruise load, the use of FT fuel resulted in no measured formation of secondary PM. In every experiment, the secondary PM was dominated by organics with minor contributions from sulfate when the engine was operated on JP-8 fuel. At both loads, FT fuel produces less secondary organic aerosol than JP-8 because of differences in the composition of the fuels and the resultant emissions. This work indicates that fuel reformulation may be a viable strategy to reduce the contribution of emissions from combustion systems to secondary organic aerosol production and ultimately ambient PM levels

Particulate Matter and Organic Vapor Emissions from a Helicopter Engine Operating on Petroleum and Fischer–Tropsch Fuels

Particle and gaseous emissions from a T63 gas-turbine engine were characterized using three fuels: standard military jet fuel (JP-8), Fischer–Tropsch (FT) synthetic fuel, and a 50:50 blend of each. Primary emissions were sampled using a dilution tunnel and sampling trains with both filters and sorbent tubes. Primary particulate matter (PM) and gaseous emissions for the neat FT and blend fuels were reduced relative to emissions when using JP-8 fuel at both idle and cruise loads. At idle load, PM mass emissions are reduced by 65% with neat FT fuel and by 50% for the 50:50 blend compared to neat JP-8 fuel. The JP-8/FT blend thus decreases emissions beyond the linear average of the emissions for the individual fuels. At idle load, FT fuel reduced total hydrocarbon emissions by 20%, while the blend showed no significant change compared to neat JP-8. At cruise load, neat FT fuel resulted in an 80% reduction in primary PM emissions and a 30% reduction in total hydrocarbon emissions compared to neat JP-8. Decreases in PM emissions at idle load come from lower elemental carbon (EC) and primary organic aerosol (POA), while at cruise load emissions, reductions are driven mainly by EC. Gas chromatography–mass spectrometry (GC–MS) and thermo-optical analysis of filter samples indicate that engine oil comprises a significant fraction of the POA emissions. When using FT fuel, POA emissions appear to be largely engine oil, but emissions with JP-8 fuel have a large fraction of partially oxidized organic material. The differences in POA composition may be due to both the presence of partially oxidized fuel as well as greater EC/soot levels when using JP-8 fuel. Thermodenuder and GC–MS measurements indicate that the POA emissions are semi-volatile; therefore, dynamic gas–particle partitioning will alter the contribution of primary emissions to ambient PM. Total gas-phase hydrocarbon emissions greatly outweigh POA emissions, and applying even moderate yields of secondary organic aerosol (SOA) will dominate over POA emissions. A high abundance of unsaturated volatile organic compounds (VOCs) in the gaseous emissions will enhance oxidation chemistry in the exhaust plume and promote the formation of SOA

Reduced Ultrafine Particle Concentration in Urban Air: Changes in Nucleation and Anthropogenic Emissions

Nucleation is an important source of ambient ultrafine particles (UFP). We present observational evidence of the changes in the frequency and intensity of nucleation events in urban air by analyzing long-term particle size distribution measurements at an urban background site in Pittsburgh, Pennsylvania during 2001–2002 and 2016–2017. We find that both frequency and intensity of nucleation events have been reduced by 40–50% over the past 15 years, resulting in a 70% reduction in UFP concentrations from nucleation. On average, the particle growth rates are 30% slower than 15 years ago. We attribute these changes to dramatic reductions in SO₂ (more than 90%) and other pollutant concentrations. Overall, UFP concentrations in Pittsburgh have been reduced by ∼48% in the past 15 years, with a ∼70% reduction in nucleation, ∼27% in weekday local sources (e.g., weekday traffic), and 49% in the regional background. Our results highlight that a reduction in anthropogenic emissions can considerably reduce nucleation events and UFP concentrations in a polluted urban environment