Sonya Collier

Real-time black carbon emission factor measurements from light duty vehicles.

Eight light-duty gasoline low emission vehicles (LEV I) were tested on a Chassis dynamometer using the California Unified Cycle (UC) at the Haagen-Smit vehicle test facility at the California Air Resources Board in El Monte, CA during September 2011. The UC includes a cold start phase followed by a hot stabilized running phase. In addition, a light-duty gasoline LEV vehicle and ultralow emission vehicle (ULEV), and a light-duty diesel passenger vehicle and gasoline direct injection (GDI) vehicle were tested on a constant velocity driving cycle. A variety of instruments with response times ≥0.1 Hz were used to characterize how the emissions of the major particulate matter components varied for the LEVs during a typical driving cycle. This study focuses primarily on emissions of black carbon (BC). These measurements allowed for the determination of BC emission factors throughout the driving cycle, providing insights into the temporal variability of BC emission factors during different phases of a typical driving cycle.

Regional Influence of Aerosol Emissions from Wildfires Driven by Combustion Efficiency: Insights from the BBOP Campaign

Wildfires are important contributors to atmospheric aerosols and a large source of emissions that impact regional air quality and global climate. In this study, the regional and nearfield influences of wildfire emissions on ambient aerosol concentration and chemical properties in the Pacific Northwest region of the United States were studied using real-time measurements from a fixed ground site located in Central Oregon at the Mt. Bachelor Observatory (∼2700 m a.s.l.) as well as near their sources using an aircraft. The regional characteristics of biomass burning aerosols were found to depend strongly on the modified combustion efficiency (MCE), an index of the combustion processes of a fire. Organic aerosol emissions had negative correlations with MCE, whereas the oxidation state of organic aerosol increased with MCE and plume aging. The relationships between the aerosol properties and MCE were consistent between fresh emissions (∼1 h old) and emissions sampled after atmospheric transport (6-45 h), suggesting that biomass burning organic aerosol concentration and chemical properties were strongly influenced by combustion processes at the source and conserved to a significant extent during regional transport. These results suggest that MCE can be a useful metric for describing aerosol properties of wildfire emissions and their impacts on regional air quality and global climate.

Real-time emission factor measurements of isocyanic acid from light duty gasoline vehicles.

Exposure to gas-phase isocyanic acid (HNCO) has been previously shown to be associated with the development of atherosclerosis, cataracts and rheumatoid arthritis. As such, accurate emission inventories for HNCO are critical for modeling the spatial and temporal distribution of HNCO on a regional and global scale. To date, HNCO emission rates from light duty gasoline vehicles, operated under driving conditions, have not been determined. Here, we present the first measurements of real-time emission factors of isocyanic acid from a fleet of eight light duty gasoline-powered vehicles (LDGVs) tested on a chassis dynamometer using the Unified Driving Cycle (UC) at the California Air Resources Board (CARB) Haagen-Smit test facility, all of which were equipped with three-way catalytic converters. HNCO emissions were observed from all vehicles, in contrast to the idealized laboratory measurements. We report the tested fleet averaged HNCO emission factors, which depend strongly on the phase of the drive cycle; ranging from 0.46 ± 0.13 mg kg fuel(-1) during engine start to 1.70 ± 1.77 mg kg fuel(-1) during hard acceleration after the engine and catalytic converter were warm. The tested eight-car fleet average fuel based HNCO emission factor was 0.91 ± 0.58 mg kg fuel(-1), within the range previously estimated for light duty diesel-powered vehicles (0.21-3.96 mg kg fuel(-1)). Our results suggest that HNCO emissions from LDGVs represent a significant emission source in urban areas that should be accounted for in global and regional models.

Organic PM Emissions from Vehicles: Composition, O/C Ratio, and Dependence on PM Concentration

A suite of real-time instruments was used to sample vehicle emissions at the California Air Resources Board Haagen-Smit facility. Eight on-road, spark-ignition gasoline and three alternative vehicles were tested on a chassis dynamometer and the emissions were diluted to atmospherically relevant concentrations (0.5–30 μg/m3). An Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-MS) characterized the real-time behavior of the nonrefractory organic and inorganic particulate matter (PM) in vehicle emissions. It was found that the emission of particulate organic matter (POM) was strongly affected by engine temperature and engine load and that the emission concentrations could vary significantly by vehicle. Despite the small sample size, consistent trends in chemical characteristics were observed. The composition of vehicle POM was found to be related to overall PM mass concentration where the oxygen-to-carbon (O/C) ratio tended to increase at lower concentration and had an average value of 0.057 ± 0.047, with a range from 0.022 to 0.15. The corresponding fraction of particle-phase CO2+, or f44, ranged from 1.1% to 8.6% (average = 2.1%) and exhibited a linear variation with O/C. The average mass spectrum from all vehicles tested was also compared to those of hydrocarbon-like organic aerosol (HOA) observed in ambient air and the agreement is very high. The results of these tests offer the vehicle emissions community a first glimpse at the real-time chemical composition and variation of vehicle PM emissions for a variety of conditions and vehicle types at atmospherically relevant conditions and without chemical interferences from other primary or secondary aerosol sources. Copyright 2015 American Association for Aerosol Research

Volatility of Primary Organic Aerosol Emitted from Light Duty Gasoline Vehicles

Primary organic aerosol (POA) emitted from light duty gasoline vehicles (LDGVs) exhibits a semivolatile behavior in which heating the aerosol and/or diluting the aerosol leads to partial evaporation of the POA. A single volatility distribution can explain the median evaporation behavior of POA emitted from LDGVs but this approach is unable to capture the full range of measured POA volatility during thermodenuder (TD) experiments conducted at atmospherically relevant concentrations (2-5 μg m(-3)). Reanalysis of published TD data combined with analysis of new measurements suggest that POA emitted from gasoline vehicles is composed of two types of POA that have distinctly different volatility distributions: one low-volatility distribution and one medium-volatility distribution. These correspond to fuel combustion-derived POA and motor oil POA, respectively. Models that simultaneously incorporate both of these distributions are able to reproduce experimental results much better (R(2) = 0.94) than models that use a single average or median distribution (R(2) = 0.52). These results indicate that some fraction of POA emitted from LDGVs is essentially nonvolatile under typical atmospheric dilution levels. Roughly 50% of the vehicles tested in the current study had POA emissions dominated by fuel combustion products (essentially nonvolatile). Further testing is required to determine appropriate fleet-average emissions rates of the two POA types from LDGVs.

Wintertime water-soluble aerosol composition and particle water content in Fresno, California

The composition and concentrations of water-soluble gases and ionic aerosol components were measured from January to February 2013 in Fresno, CA, with a particle-into-liquid sampler with ion chromatography and annular denuders. The average (±1σ) ionic aerosol mass concentration was 15.0 (±9.4) µg m−3, and dominated by nitrate (61%), followed by ammonium, sulfate, chloride, potassium, nitrite, and sodium. Aerosol-phase organic acids, including formate and glycolate, and amines including methylaminium, triethanolaminium, ethanolaminium, dimethylaminium, and ethylaminium were also detected. Although the dominant species all came from secondary aerosol formation, there were primary sources of ionic aerosols as well, including biomass burning for potassium and glycolate, sea spray for sodium, chloride, and dimethylamine, and vehicles for formate. Particulate methanesulfonic acid was also detected and mainly associated with terrestrial sources. On average, the molar concentration of ammonia was 49 times greater than nitric acid, indicating that ammonium nitrate formation was limited by nitric acid availability. Particle water was calculated based on the Extended Aerosol Inorganics Model (E-AIM) thermodynamic prediction of inorganic particle water and κ-Kohler theory approximation of organic particle water. The average (±1σ) particle water concentration was 19.2 (±18.6) µg m−3, of which 90% was attributed to inorganic species. The fractional contribution of particle water to total fine particle mass averaged at 36% during this study and was greatest during early morning and night and least during the day. Based on aqueous-phase concentrations of ions calculated by using E-AIM, the average (±1σ) pH of particles in Fresno during the winter was estimated to be 4.2 (±0.2).

Influences of upwind emission sources and atmospheric processing on aerosol chemistry and properties at a rural location in the Northeastern U.S.

Continuous real-time measurements of atmospheric aerosol with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer coupled with a fast temperature-stepping thermodenuder were carried out in summer 2011 at Brookhaven National Laboratory (BNL, 40.871°N, 72.89°W) during the Department of Energy Aerosol Life Cycle Intensive Operational Period campaign. BNL was frequently downwind of emissions from the New York metropolitan area and was exposed to various combinations of anthropogenic, biogenic, and marine emissions based on air mass history. The average concentration of submicrometer aerosol (PM1) during this study was 12.6 µg m−3 with 64% of the mass being organic. Organic aerosol (OA) at BNL was found to be overwhelmingly secondary, consisting of (1) a fresher, semivolatile oxygenated organic aerosol (SV-OOA; oxygen-to-carbon ratio (O/C) = 0.54; 63% of OA mass) that was strongly influenced by transported urban plumes; (2) a regional, more aged, low-volatility OOA (LV-OOA; O/C = 0.97; 29% of OA mass) influenced by aqueous-phase processing; and (3) a nitrogen-enriched OA (NOA; nitrogen-to-carbon ratio (N/C) = 0.185; 8% of OA mass) likely composed of amine salts formed from acid-base reactions in industrial emissions. Urban emissions from the New York metropolitan areas to the W and SW in particular led to elevated PM1 mass concentration and altered aerosol composition at BNL. Transported urban plumes and local biogenic emissions likely interacted to enhance secondary organic aerosol production, primarily represented by SV-OOA. These results suggest an important role that urban anthropogenic emissions play in affecting ambient PM concentration, composition, and physical-chemical properties at rural areas in the Northeast U.S.

Influence of emissions and aqueous processing on particles containing black carbon in a polluted urban environment: Insights from a soot particle – aerosol mass spectrometer

Inorganic and organic coatings on black carbon (BC) particles can enhance light absorption and affect atmospheric lifetimes of BC-containing particles and thus have significant implications for climate. To study the physical and chemical characteristics of atmospheric BC and BC-associated coatings, a soot-particle aerosol mass spectrometer (SP-AMS) was deployed during the winter of 2014-2015 in Fresno, a city located in the San Joaquin Valley of California, to selectively analyze BC-containing particles. Comparing SP-AMS measurements to those from the collocated single particle soot photometer (SP2) and high resolution aerosol mass spectrometer (HR-AMS), we found that 17% of total submicrometer aerosol mass was associated with BC-containing particles, suggesting that a majority of the fine particles in Fresno contained no BC. Most BC-containing particles appeared to be associated with residential wood burning and vehicular traffic. These particles typically had a bulk-average mass ratio of coating-to-BC (Rcoat/rBC) less than 2. However, during periods of persistent fog larger Rcoat/rBC values were observed, with the coatings primarily composed of secondary inorganic and organic components that likely resulted from aqueous-phase processing. Specifically, compared to periods with less fog, the BC coating increased in concentration and contained a larger fraction of nitrate and oxidized organic matter. The size distributions of BC and associated organic coating were generally centered around 300 nm in vacuum aerodynamic diameter. However, during foggy periods BC had an additional peak at ~ 400 nm and organics and nitrate displayed a prominent mode in the accumulation size range.