Nathan M. Kreisberg

On-road measurement of fine particle and nitrogen oxide emissions from light- and heavy-duty motor vehicles

Abstract An updated assessment of fine particle emissions from light- and heavy-duty vehicles is needed due to recent changes to the composition of gasoline and diesel fuel, more stringent emission standards applying to new vehicles sold in the 1990s, and the adoption of a new ambient air quality standard for fine particulate matter (PM2.5) in the United States. This paper reports the measurement of emissions from vehicles in a northern California roadway tunnel during summer 1997. Separate measurements were made of uphill traffic in two tunnel bores: one bore carried both light-duty vehicles and heavy-duty diesel trucks, and the second bore was reserved for light-duty vehicles. Ninety-eight percent of the light-duty vehicles were gasoline-powered. In the tunnel, heavy-duty diesel trucks emitted 24, 37, and 21 times more fine particle, black carbon, and sulfate mass per unit mass of fuel burned than light-duty vehicles. Heavy-duty diesel trucks also emitted 15–20 times the number of particles per unit mass of fuel burned compared to light-duty vehicles. Fine particle emissions from both vehicle classes were composed mostly of carbon; diesel-derived particulate matter contained more black carbon (51±11% of PM2.5 mass) than did light-duty fine particle emissions (33±4%). Sulfate comprised only 2% of total fine particle emissions for both vehicle classes. Sulfate emissions measured in this study for heavy-duty diesel trucks are significantly lower than values reported in earlier studies conducted before the introduction of low-sulfur diesel fuel. This study suggests that heavy-duty diesel vehicles in California are responsible for nearly half of oxides of nitrogen emissions and greater than three-quarters of exhaust fine particle emissions from on-road motor vehicles.

Effects of anthropogenic emissions on aerosol formation from isoprene and monoterpenes in the southeastern United States

Significance Atmospheric secondary organic aerosol has substantial impacts on climate, air quality, and human health. However, the formation mechanisms of secondary organic aerosol remain uncertain, especially on how anthropogenic pollutants (from human activities) control aerosol formation from biogenic volatile organic compounds (emitted by vegetation) and the magnitude of anthropogenic influences. Although possible mechanisms have been proposed based on laboratories studies, a coherent understanding of anthropogenic−biogenic interactions in ambient environments has not emerged. Here, we provide direct observational evidence that secondary organic aerosol formed from biogenic isoprene and monoterpenes is greatly mediated by anthropogenic SO2 and NOx emissions based on integrated ambient measurements and laboratory studies. Secondary organic aerosol (SOA) constitutes a substantial fraction of fine particulate matter and has important impacts on climate and human health. The extent to which human activities alter SOA formation from biogenic emissions in the atmosphere is largely undetermined. Here, we present direct observational evidence on the magnitude of anthropogenic influence on biogenic SOA formation based on comprehensive ambient measurements in the southeastern United States (US). Multiple high-time-resolution mass spectrometry organic aerosol measurements were made during different seasons at various locations, including urban and rural sites in the greater Atlanta area and Centreville in rural Alabama. Our results provide a quantitative understanding of the roles of anthropogenic SO2 and NOx in ambient SOA formation. We show that isoprene-derived SOA is directly mediated by the abundance of sulfate, instead of the particle water content and/or particle acidity as suggested by prior laboratory studies. Anthropogenic NOx is shown to enhance nighttime SOA formation via nitrate radical oxidation of monoterpenes, resulting in the formation of condensable organic nitrates. Together, anthropogenic sulfate and NOx can mediate 43–70% of total measured organic aerosol (29–49% of submicron particulate matter, PM1) in the southeastern US during summer. These measurements imply that future reduction in SO2 and NOx emissions can considerably reduce the SOA burden in the southeastern US. Updating current modeling frameworks with these observational constraints will also lead to more accurate treatment of aerosol formation for regions with substantial anthropogenic−biogenic interactions and consequently improve air quality and climate simulations.

An In-Situ Instrument for Speciated Organic Composition of Atmospheric Aerosols: Thermal Desorption Aerosol GC/MS-FID (TAG)

We introduce a new in-situ instrument, Thermal desorption Aerosol GC/MS-FID (TAG), capable of hourly measurements of speciated organic compounds in atmospheric aerosols. Aerosol samples are collected into a thermal desorption cell by means of humidification and inertial impaction. The sample is thermally desorbed and transferred with helium carrier gas into a gas chromatography (GC) column, with subsequent detection by both quadrupole mass spectrometer (MS) and a flame ionization detector (FID). The collection and analysis steps are automated, yielding around the clock speciation. This approach builds on the extensive body of knowledge available for quantification and source apportionment of organic aerosols from past research using filter-based GC/MS analyses, but it is the first instrument to achieve in-situ time resolved measurements for an essentially unlimited number of samples, making it possible to analyze changes in organic aerosol speciation over timescales ranging from hours to seasons.

Ultrafine particle concentrations and exposures in seven residences in northern California

UNLABELLED Human exposures to ultrafine particles (UFP) are poorly characterized given the potential associated health risks. Residences are important sites of exposure. To characterize residential exposures to UFP in some circumstances and to investigate governing factors, seven single-family houses in California were studied during 2007-2009. During multiday periods, time-resolved particle number concentrations were monitored indoors and outdoors and information was acquired concerning occupancy, source-related activities, and building operation. On average, occupants were home for 70% of their time. The geometric mean time-average residential exposure concentration for 21 study subjects was 14,500 particles per cm(3) (GSD = 1.8; arithmetic mean ± standard deviation = 17,000 ± 10,300 particles per cm(3)). The average contribution to residential exposures from indoor episodic sources was 150% of the contribution from particles of outdoor origin. Unvented natural-gas pilot lights contributed up to 19% to exposure for the two households where present. Episodic indoor source activities, most notably cooking, caused the highest peak exposures and most of the variation in exposure among houses. Owing to the importance of indoor sources and variations in the infiltration factor, residential exposure to UFP cannot be characterized by ambient measurements alone. PRACTICAL IMPLICATIONS Indoor and outdoor sources each contribute to residential ultrafine particle (UFP) concentrations and exposures. Under the conditions investigated, peak exposure concentrations indoors were associated with cooking, using candles, or the use of a furnace. Active particle removal systems can mitigate exposure by reducing the persistence of particles indoors. Eliminating the use of unvented gas pilot lights on cooking appliances could also be beneficial. The study results indicate that characterization of human exposure to UFP, an air pollutant of emerging public health concern, cannot be accomplished without a good understanding of conditions inside residences.

In situ measurements of gas/particle-phase transitions for atmospheric semivolatile organic compounds

An understanding of the gas/particle-phase partitioning of semivolatile compounds is critical in determining atmospheric aerosol formation processes and growth rates, which in turn affect global climate and human health. The Study of Organic Aerosol at Riverside 2005 campaign was performed to gain a better understanding of the factors responsible for aerosol formation and growth in Riverside, CA, a region with high concentrations of secondary organic aerosol formed through the phase transfer of low-volatility reaction products from the oxidation of precursor gases. We explore the ability of the thermal desorption aerosol gas chromatograph (TAG) to measure gas-to-particle-phase transitioning for several organic compound classes (polar and nonpolar) found in the ambient Riverside atmosphere by using in situ observations of several hundred semivolatile organic compounds. Here we compare TAG measurements to modeled partitioning of select semivolatile organic compounds. Although TAG was not designed to quantify the vapor phase of semivolatile organics, TAG measurements do distinguish when specific compounds are dominantly in the vapor phase, are dominantly in the particle phase, or have both phases present. Because the TAG data are both speciated and time-resolved, this distinction is sufficient to see the transition from vapor to particle phase as a function of carbon number and compound class. Laboratory studies typically measure the phase partitioning of semivolatile organic compounds by using pure compounds or simple mixtures, whereas hourly TAG phase partitioning measurements can be made in the complex mixture of thousands of polar/nonpolar and organic/inorganic compounds found in the atmosphere.

Atmospheric Size Distributions Measured by Differential Mobility Optical Particle Size Spectrometry

ABSTRACT A differential mobility and optical particle size spectrometer (DMOPSS) was developed to measure ambient size distributions based on geometric particle diameter in the size range of 0.1 to 1.0 μm diameter. The DMOPSS consists of a high-flow differential mobility analyzer (HF-DMA) followed by an optical particle counter (OPC) and condensation nucleus counter (CNC) operating in parallel. The OPC and CNC sample monodisperse aerosol of known geometric diameter from the HF-DMA output or, alternatively, polydisperse aerosol with known dilution directly from the ambient air. The monodisperse samples are used to create time-dependent calibrations of the OPC, providing optical response versus geometric size for the ambient aerosol under study. The direct ambient measurements are then reduced, using this ambient-based calibration. A field test of the DMOPSS system was performed in the summer of 1992 at Meadview, Arizona, where more than 12,000 size spectra were collected; they consisted of roughly one-thir...

Ultrafine particle concentrations and exposures in six elementary school classrooms in northern California

UNLABELLED Potential health risks may result from environmental exposure to ultrafine particles (UFP), i.e., those smaller than 0.1 μm in diameter. One important exposure setting that has received relatively little attention is school classrooms. We made time-resolved, continuous measurements of particle number (PN) concentrations for 2-4 school days per site (18 days total) inside and outside of six classrooms in northern California during normal occupancy and use. Additional time-resolved information was gathered on ventilation conditions, occupancy, and classroom activity. Across the six classrooms, average indoor PN concentrations when students were present were 5200-16,500/cm(3) (overall average 10,800/cm(3)); corresponding outdoor concentrations were 9000-26,000/cm(3) (overall average 18,100/cm(3)). Average indoor levels were higher when classrooms were occupied than when they were unoccupied because of higher outdoor concentrations and higher ventilation rates during occupancy. In these classrooms, PN exposures appear to be primarily attributable to outdoor sources. Indoor emission sources (candle use, cooking on an electric griddle, use of a heater, use of terpene-containing cleaning products) were seen to affect indoor PN concentrations only in a few instances. The daily-integrated exposure of students in these six classrooms averaged 52,000/cm(3) h/day for the 18 days monitored. PRACTICAL IMPLICATIONS This study provides data and insight concerning the UFP exposure levels children may encounter within classrooms and the factors that most significantly affect these levels in an urban area in northern California. This information can serve as a basis to guide further study of childrens UFP exposure and the potential associated health risks.

Quantification of Hourly Speciated Organic Compounds in Atmospheric Aerosols, Measured by an In-Situ Thermal Desorption Aerosol Gas Chromatograph (TAG)

The Thermal desorption Aerosol Gas chromatograph (TAG) is a recently developed instrument for the in-situ, hourly measurement of speciated organic compounds in atmospheric aerosols. This paper presents a method for the in-field calibration of this instrument, with the objective of providing quantitative concentrations for a large suite of low polarity organic compounds. A new collection and thermal desorption cell was developed that incorporates an injection port for in-situ calibrations with liquid standard mixtures. Two classes of injection standards, instrument tracking and auxiliary, provide the means to calibrate the instrument in the field for a wide range of compounds. A routinely injected tracking standard suite of compounds generates a time-dependent correction of detector drift through the course of a measurement study that accounts for the bulk of the change in response of the TAG instrument. Injection response data for the tracking standard is also used to measure instrument precision and limits of quantitation. Auxiliary standards extend the range of compounds calibrated through use of relative response factors. The accuracy of this in-situ calibration approach is assessed through comparisons of TAG analyzed reference filter punches to published NIST assay values. A subset of compound classes, alkanes and PAHs, are used to illustrate the method and provide a means of reducing an 11-day period of data collected in Riverside, CA during the fall of 2005.

Particle Size Relationships at the Fresno Supersite

Abstract Aerosol size distributions are presented for a winter intensive study at the Fresno Supersite. The size distributions were consistent with and predictive for continuous PM2.5 measured by beta attenuation. They varied temporally with respect to source type and intensity, with the smallest mean diameters associated with high NOx concentrations during weekday morning rush hours. Conversely, small and large particle and black carbon (BC) concentrations were higher during Sunday and weekday evenings in response to traffic and residential wood combustion emissions. Ambient PM2.5 light scattering (Bsp) was precisely but systematically underestimated during winter, probably because of heating in the sample shelter.

Insights into Secondary Organic Aerosol Formation Mechanisms from Measured Gas/Particle Partitioning of Specific Organic Tracer Compounds

In situ measurements of organic compounds in both gas and particle phases were made with a thermal desorption aerosol gas chromatography (TAG) instrument. The gas/particle partitioning of phthalic acid, pinonaldehyde, and 6,10,14-trimethyl-2-pentadecanone is discussed in detail to explore secondary organic aerosol (SOA) formation mechanisms. Measured fractions in the particle phase (f(part)) of 6,10,14-trimethyl-2-pentadecanone were similar to those expected from the absorptive gas/particle partitioning theory, suggesting that its partitioning is dominated by absorption processes. However, f(part) of phthalic acid and pinonaldehyde were substantially higher than predicted. The formation of low-volatility products from reactions of phthalic acid with ammonia is proposed as one possible mechanism to explain the high f(part) of phthalic acid. The observations of particle-phase pinonaldehyde when inorganic acids were fully neutralized indicate that inorganic acids are not required for the occurrence of reactive uptake of pinonaldehyde on particles. The observed relationship between f(part) of pinonaldehyde and relative humidity suggests that the aerosol water plays a significant role in the formation of particle-phase pinonaldehyde. Our results clearly show it is necessary to include multiple gas/particle partitioning pathways in models to predict SOA and multiple SOA tracers in source apportionment models to reconstruct SOA.