Cheol-Heon Jeong

Inter-Comparison of a Fast Mobility Particle Sizer and a Scanning Mobility Particle Sizer Incorporating an Ultrafine Water-Based Condensation Particle Counter

An Ultrafine Water-based Condensation Particle Counter (UWCPC), a Scanning Mobility Particle Sizer (SMPS) incorporating an UWCPC, and a Fast Mobility Particle Sizer (FMPS) were deployed to determine the number and size distribution of ultrafine particles. Comparisons of particle number concentrations measured by the UWCPC, SMPS, and FMPS were conducted to evaluate the performance of the two particle sizers using ambient particles as well as lab generated artificial particles. The SMPS number concentration was substantially lower than the FMPS (FMPS/SMPS = 1.56) measurements mainly due to the diffusion losses of particles in the SMPS. The diffusion loss corrected SMPS (C-SMPS) number concentration was on average ∼ 15% higher than the FMPS data (FMPS/C-SMPS = 0.87). Good correlation between the C-SMPS and FMPS was also observed for the total particle number concentrations in the size range 6 nm to 100 nm measured at a road-side urban site (r2 = 0.91). However, the particle size distribution measured by the C-SMPS was quite different from the size distribution measured by the FMPS. An empirical correction factor for each size bin was obtained by comparing the FMPS data to size-segregated UWCPC number concentrations for atmospheric particles. The application of the correction factor to the FMPS data (C-FMPS) greatly improved the agreement of the C-SMPS and C-FMPS size distributions. The agreement of the total particle concentrations also improved to well within 10% (C-FMPS/C-SMPS = 0.95).

Mass Absorption Cross-Section of Ambient Black Carbon Aerosol in Relation to Chemical Age

Three differing techniques were used to measure ambient black carbon (BC) aerosols in downtown Toronto through 20 December 2006 to 23 January 2007. These techniques were thermal analysis, as performed by a Sunset Labs OCEC Analyzer (OCEC); light attenuation, as performed by an Aethalometer (AE); and photoacoustic analysis, as performed by a Photoacoustic Instrument (PA). These measurements of ambient PM 2.5 were used to investigate the effects of coating thickness on BC Mass Absorption Cross-section (MAC). MAC values were determined by comparing 880 nm and 370 nm AE measurements and PA measurements of b abs (absorption coefficient, Mm–1) to the OCEC measurements. Based on mass size distributions and supporting criteria, the PM 2.5 was classified as fresh, semi-aged, or aged. The average MAC values in these categories, based on the PA measurements, were 9.3 ± 1.8, 9.9 ± 2.0, and 9.3 ± 2.2 m 2 /g (mean ± standard deviation), respectively, suggesting that any difference in coating thickness as a result of aging, on the time scale observed, did not produce a difference in MAC. In a second type of experiment, a thermodenuder was installed upstream of the AE, PA, and OCEC and samples were heated to 340°C in order to evaporate volatile and semi-volatile components within the coating. Based on the PA measurements, the average MAC values of these heated samples, for the fresh, semi-aged, and aged categories were 7.7 ± 2.2, 6.9 ± 2.2, and 9.1 ± 2.0 m 2 /g, respectively. Similar differences in MAC were also observed by the AE. The decrease in MAC in the fresh and semi-aged samples was interpreted in terms of the degree of coating of the PM 2.5 . Results agreed well with predictions made by absorption amplification theory and had ramifications for calibration of filter-base attenuation and photoacoustic instruments.

Cloud and Fog Processing Enhanced Gas-to-Particle Partitioning of Trimethylamine

An aerosol time-of-flight mass spectrometer (ATOFMS) was used to detect trimethylamine (TMA) in 0.52-1.9 μm particles at urban and rural sites in Southern Ontario during the summer and winter of 2007. During the summer, TMA-containing particles were observed exclusively during high relative humidity or fog events at both the urban and rural sites. In the wintertime, greater concentrations of TMA-containing particles were linked to cloud processing of aerosol in air masses originating from over agricultural and livestock areas. A laboratory study revealed that, at high relative humidity (∼ 100%), gas phase TMA at concentrations ranging from 2 to 20,000 ppt partitions preferentially to acidic particles present in the ambient air. On the basis of the field and laboratory studies, it appears that gas phase TMA present in ambient air partitions onto pre-existing particles preferentially during periods of acidic cloud/fog processing, leading to the presence of TMA-containing particles in the 0.52-1.9 μm size range.

Influence of atmospheric dispersion and new particle formation events on ambient particle number concentration in Rochester, United States, and Toronto, Canada

Abstract Continuous measurements of particle number concentrations were performed in Rochester, NY, and Toronto, Ontario, Canada during the 2003 calendar year. Strong seasonal dependency in particle number concentration was observed at two sites. The average number concentration of ambient particles was 9670 ± 6960 cm−3 in Rochester, whereas in Toronto the average number of particles was 28,010 ± 13,350 cm−3. The particle number concentrations were higher in winter months than in summer months by a factor of 1.5 in Rochester and 1.6 in Toronto. In general, there were also distinct diurnal variations of aerosol number concentration. The highest weekdays/weekends ratio of number concentration was typically observed during the rush-hour period in winter months with a ratio of 2.1 in Rochester and 2.0 in Toronto. The correlation in the total particle number concentrations between the two urban sites was stronger in winter because of the common urban traffic patterns, but weaker in summer because of local sulfur dioxide (SO2) related particle formation events in Rochester in the summer. Strong morning particle formation events were frequently observed during colder winter months. Good correlations between particle number and carbon monoxide (CO) as well as temperature suggested that motor-vehicle emissions lead to the formation of new particles as the exhaust mixes with the cold air. Regional nucleation and growth events frequently occurred in April. Local SO2-related particle formation events most frequently occurred in August. SO2 and UV-B were highly correlated with particle concentration, suggesting a high association of photochemical processes with these local events. A high directionality in a northerly direction was observed for particle number and SO2, indicating the influence of point sources located north of Rochester.

Light-absorbing properties of ambient black carbon and brown carbon from fossil fuel and biomass burning sources

The optical properties of ambient black carbon-containing particles and the composition of their associated coatings were investigated at a downtown site in Toronto, Canada, for 2 weeks in June 2013. The objective was to assess the relationship between black carbon (BC) coating composition/thickness and absorption. The site was influenced by emissions from local vehicular traffic, wildfires in Quebec, and transboundary fossil fuel combustion emissions in the United States. Mass concentrations of BC and associated nonrefractory coatings were measured using a soot particle–aerosol mass spectrometer (SP-AMS), while aerosol absorption and scattering were measured using a photoacoustic soot spectrometer (PASS). Absorption enhancement was investigated both by comparing ambient and thermally denuded PASS absorption data and by relating absorption data to BC mass concentrations measured using the SP-AMS. Minimal absorption enhancement attributable to lensing at 781 nm was observed for BC using both approaches. However, brown carbon was detected when the site was influenced by wildfire emissions originating in Quebec. BC coating to core mass ratios were highest during this period (~7), and while direct absorption by brown carbon resulted in an absorption enhancement at 405 nm (>2.0), no enhancement attributable to lensing at 781 nm was observed. The efficiency of BC coating removal in the denuder decreased substantially when wildfire-related organics were present and may represent an obstacle for future similar studies. These findings indicate that BC absorption enhancement due to lensing is minimal for downtown Toronto, and potentially other urban locations, even when impacted by long-range transport events.

Identification of the sources and geographic origins of black carbon using factor analysis at paired rural and urban sites.

Black carbon particles, composed of forms of elemental carbon (EC), contribute significantly to regional and global warming. The origins of EC were examined in southeastern Canada as part of a source apportionment study using positive matrix factorization (PMF), performed on long-term PM2.5 chemical speciation data collected at two paired rural and urban sites. Comparisons of the urban and rural sites revealed a previously unrecognized EC-rich factor that accounted for 41-56% of the total EC in this region. This factor was characterized by the more thermally stable EC fractions that exhibit strong light absorption characteristics. While these EC fractions are often attributed to local diesel emissions, this interpretation was rejected for several reasons. The EC-rich factor was present in similar temporal patterns at both the high-traffic urban and low-traffic rural sites across this 600 km region. The geographic origins of the EC-rich factor were found to be Ohio and Western Pennsylvania regions with heavy industry and multiple coal-based electrical generating stations. The direct radiative forcing due to this EC-rich factor was roughly estimated to be +0.2 W m(-2), which represented a substantial portion of the aerosol induced warming in the region. Thus, this region was impacted by an important unidentified source of EC associated with long-range transport.

Assessing the Climate Trade-Offs of Gasoline Direct Injection Engines.

Compared to port fuel injection (PFI) engine exhaust, gasoline direct injection (GDI) engine exhaust has higher emissions of black carbon (BC), a climate-warming pollutant. However, the relative increase in BC emissions and climate trade-offs of replacing PFI vehicles with more fuel efficient GDI vehicles remain uncertain. In this study, BC emissions from GDI and PFI vehicles were compiled and BC emissions scenarios were developed to evaluate the climate impact of GDI vehicles using global warming potential (GWP) and global temperature potential (GTP) metrics. From a 20 year time horizon GWP analysis, average fuel economy improvements ranging from 0.14 to 14% with GDI vehicles are required to offset BC-induced warming. For all but the lowest BC scenario, installing a gasoline particulate filter with an 80% BC removal efficiency and <1% fuel penalty is climate beneficial. From the GTP-based analysis, it was also determined that GDI vehicles are climate beneficial within <1-20 years; longer time horizons were associated with higher BC scenarios. The GDI BC emissions spanned 2 orders of magnitude and varied by ambient temperature, engine operation, and fuel composition. More work is needed to understand BC formation mechanisms in GDI engines to ensure that the climate impacts of this engine technology are minimal.

Field Measurements of Gasoline Direct Injection Emission Factors: Spatial and Seasonal Variability.

Four field campaigns were conducted between February 2014 and January 2015 to measure emissions from light-duty gasoline direct injection (GDI) vehicles (2013 Ford Focus) in an urban near-road environment in Toronto, Canada. Measurements of CO2, CO, NOx, black carbon (BC), benzene, toluene, ethylbenzene-xylenes (BTEX), and size-resolved particle number (PN) were recorded 15 m from the roadway and converted to fuel-based emission factors (EFs). Other than for NOx and CO, the GDI engine had elevated emissions compared to the Toronto fleet, with BC EFs in the 73rd percentile, BTEX EFs in the 80-90th percentile, and PN EFs in the 75th percentile during wintertime measurements. Additionally, for three campaigns, a second platform for measuring PN and CO2 was placed 1.5-3 m from the roadway to quantify changes in PN with distance from point of emission. GDI vehicle PN EFs were found to increase by up to 240% with increasing distance from the roadway, predominantly due to an increasing fraction of sub-40 nm particles. PN and BC EFs from the same engine technology were also measured in the laboratory. BC EFs agreed within 20% between the laboratory and real-world measurements; however, laboratory PN EFs were an order of magnitude lower due to exhaust conditioning.

Murine precision-cut lung slices exhibit acute responses following exposure to gasoline direct injection engine emissions.

Gasoline direct injection (GDI) engines are increasingly prevalent in the global vehicle fleet. Particulate matter emissions from GDI engines are elevated compared to conventional gasoline engines. The pulmonary effects of these higher particulate emissions are unclear. This study investigated the pulmonary responses induced by GDI engine exhaust using an ex vivo model. The physiochemical properties of GDI engine exhaust were assessed. Precision cut lung slices were prepared using Balb/c mice to evaluate the pulmonary response induced by one-hour exposure to engine-out exhaust from a laboratory GDI engine operated at conditions equivalent to vehicle highway cruise conditions. Lung slices were exposed at an air-liquid interface using an electrostatic aerosol in vitro exposure system. Particulate and gaseous exhaust was fractionated to contrast mRNA production related to polycyclic aromatic hydrocarbon (PAH) metabolism and oxidative stress. Exposure to GDI engine exhaust upregulated genes involved in PAH metabolism, including Cyp1a1 (2.71, SE=0.22), and Cyp1b1 (3.24, SE=0.12) compared to HEPA filtered air (p<0.05). GDI engine exhaust further increased Cyp1b1 expression compared to filtered GDI engine exhaust (i.e., gas fraction only), suggesting this response was associated with the particulate fraction. Exhaust particulate was dominated by high molecular weight PAHs. Hmox1, an oxidative stress marker, exhibited increased expression after exposure to GDI (1.63, SE=0.03) and filtered GDI (1.55, SE=0.04) engine exhaust compared to HEPA filtered air (p<0.05), likely attributable to a combination of the gas and particulate fractions. Exposure to GDI engine exhaust contributes to upregulation of genes related to the metabolism of PAHs and oxidative stress.

Rapid physical and chemical transformation of traffic-related atmospheric particles near a highway

The health of a substantial portion of urban populations is potentially being impacted by exposure to traffic–related atmospheric pollutants. To better understand the rapid physical and chemical transformation of these pollutants, the number size distributions of non–volatile traffic–related particles were investigated at different distances from a major highway. Particle volatility measurements were performed upwind and downwind of the highway using a fast mobility particle sizing spectrometer with a thermodenuder on a mobile laboratory. The number concentration of non–denuded ultrafine particles decreased exponentially with distance from the highway, whereas a more gradual gradient was observed for non–volatile particles. The non–volatile number concentration at 27 m was higher than that at 280 m by a factor of approximately 3, and the concentration at 280 m was still higher than that upwind of the highway. The proportion of non–volatile particles increased away from the highway, representing 36% of the total particle number at 27 m, 62% at 280 m, and 81% at the upwind site. A slight decrease in the geometric mean diameter of the non–volatile particle size distributions from approximately 35 nm to 30 nm was found between 27 m and 280 m, in contrast to the growth of non–denuded particles with increasing distance from the highway. Single particle analysis results show that the contribution of elemental carbon (EC)–rich particle types at 27 m was higher than the contribution at 280 m by a factor of approximately 2. The findings suggest that people living or spending time near major roadways could be exposed to elevated number concentrations of nucleation–mode volatile particles ( 100 nm). The impact of the highway emissions on air quality was observable up to 300 m.