Source Of Ultrafine Particles Research Articles

Evidence for the role of ion‐induced particle formation during an atmospheric nucleation event observed in Tropospheric Ozone Production about the Spring Equinox (TOPSE)

Various in situ measurements show evidence of new particle formation over a wide range of latitudes in the middle to upper troposphere and lower stratosphere. However, the exact mechanism of new particle formation is still uncertain. Using a combination of satellite‐derived brightness temperature, air parcel backward trajectory information, in situ measurements of aerosol and precursor gases and an aerosol microphysical model driven by parameterized ion‐induced nucleation, we investigate the mechanism responsible for, and factors leading to, new particle formation in the middle to upper troposphere during the Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment. The number concentrations of modeled ultrafine particles of diameters 3 to 4 nm (N3–4nm) and 3 to 8 nm (N3–8nm) are consistent with in situ measurements indicating that new particle formation likely occurred by ion‐induced nucleation a day prior to the time of measurement. A reduction in preexisting aerosol surface area in a region of cloud outflow probably triggered particle nucleation. These studies indicate that under typical middle to upper troposphere conditions, the ion mechanism is likely an important source of ultrafine particles, and these newly formed particles can grow to act as cloud condensation nuclei.

Modal structure and spatial?temporal variations of urban and suburban aerosols in Helsinki?Finland

Abstract Particle number size distributions were measured in the urban and suburban atmosphere of Helsinki. In the absence of a direct traffic emission influence, the temporal variation of the aerosol particle number concentrations and their particle size distribution characteristics can be generalized within the Helsinki metropolitan region. In general, the particle number size distributions are characterized by three modes: nucleation ( 90 nm). Under certain conditions such as overlapping between the nucleation and Aitken modes, it is possible to characterize the particle number size distributions by two modes: ultrafine mode ( 100 nm). Traffic combustions are considered as one of the major sources of ultrafine particles (UFP, D p 100 nm ) in the urban atmosphere. The total particle number concentration is highest in the urban centers (as high as 140 000 cm −3 , more than 90% is UFP), In general, 70–80% of the submicrometer particle number concentration is UFP in the suburban atmosphere. Close to major highways, the geometric mean diameters of the submicrometer modes are smaller and the total number concentrations can exceed 60 000 cm −3 (more than 60% is nucleation mode particles). According to the wind speed and temperature analysis, the submicrometer aerosol particles in the urban and suburban atmosphere consist of two components: UFP that is diluted with wind speeds and inversely proportional to the ambient temperature, and particles larger than 100 nm in diameter that is re-suspended with wind and proportional to the ambient temperature. The correlation analysis showed that UFP number concentrations are best correlated within the urban areas. Particles larger than 100 nm showed good correlation factors (about 0.80) within the Helsinki metropolitan area, which is an indication of similar kinds of aerosols such as regional transported particles.

Size-Fractionated Measurements of Ambient Ultrafine Particle Chemical Composition in Los Angeles Using the NanoMOUDI

Ambient ultrafine particles have gained attention with recent evidence showing them to be more toxic than larger ambient particles. Few studies have investigated the distribution of chemical constituents within the ultrafine range. The current study explores the size-fractionated ultrafine (10-180 nm) chemical composition at urban source sites (USC and Long Beach) and inland receptor sites (Riverside and Upland) in the Los Angeles basin over three different seasons. Size-fractionated ultrafine particles were collected by a NanoMOUDI over a period of 2 weeks at each site. Measurements of ultrafine mass concentrations varied from 0.86 to 3.5 microg/m3 with the highest concentrations observed in the fall. The chemical composition of ultrafine particles ranged from 32 to 69% for organic carbon (OC), 1-34% for elemental carbon (EC), 0-24% for sulfate, and 0-4% for nitrate. A distinct OC mode was observed between 18 and 56 nm in the summer, possibly indicating photochemical secondary organic aerosol formation. The EC levels are higher in winter at the source sites due to lower inversion heights and are higher in summer at the receptor sites due to increased long-range transport from upwind source areas. Nitrate and sulfate were measurable only in the larger particle size ranges of ultrafine PM. Collocated continuous measurements of particle size distributions and gaseous pollutants helped to differentiate ultrafine particle sources at each site.

Nucleation Events During the Pittsburgh Air Quality Study: Description and Relation to Key Meteorological, Gas Phase, and Aerosol Parameters Special Issue ofAerosol Science and Technologyon Findings from the Fine Particulate Matter Supersites Program

During the Pittsburgh Air Quality Study (PAQS) aerosol size distributions between 3 nm and 680 nm were measured between July 2001 and June 2002. These distributions have been analyzed to assess the importance of nucleation as a source of ultrafine particles in Pittsburgh and the surrounding areas. The analysis shows nucleation on 50% of the study days and regional-scale formation of ultrafine particles on 30% of the days. Nucleation occurred during all seasons, but it was most frequent in fall and spring and least frequent in winter. Regional nucleation was most common on sunny days with below average PM2.5 concentrations. Local nucleation events were usually associated with elevated SO2 concentrations. The observed nucleation events ranged from weak events with only a slight increase in the particle number to relatively intense events with increases of total particle counts between 50,000 cm−3 up to 150,000 cm−3. Averaging all days of the study, days with nucleation events had number concentrations peaking at around noon at about 45,000 cm−3. This is compared to work days without nucleation, when the daily maximum was 8 am at 23,000 cm−3, and to weekends without nucleation, when the daily maximum was at noon at 16,000 cm−3. Twenty-four-hour average number concentrations were approximately 40% higher on days with nucleation compared to those without. Nucleation was typically observed starting around 9 am EST, although the start of nucleation events was later in winter and earlier in summer. The nucleation events are fairly well correlated with the product of [UV intensity * SO2 concentration] and also depend on the effective area available for condensation. This indicates that H2SO4 is a component of the new particles. Published correlations for nucleation by binary H2SO4—H2O cannot explain the observed nucleation frequency and intensity, suggesting that an additional component (perhaps ammonia) is participating in the particle formation.

Characterization of Ultrafine Particle Number Concentration and Size Distribution During a Summer Campaign in Southwest Detroit

This paper presents results from a study conducted in southwest Detroit from July 20 to July 30, 2002, to characterize ambient ultrafine particles (d p < 0.1 μm), and to examine the effect of local sources and meteorological parameters on the ultrafine number concentration and size distribution. The number concentrations of ambient particles in the size range of 0.01–0.43 μm were obtained from a scanning mobility particle sizer (SMPS). Meteorological parameters including ambient temperature, relative humidity, wind speed, wind direction, rainfall, and solar radiation flux were also monitored concurrently atop a 10-m tower. On average, ultrafine particles ranged from 1.4 × 104 to 2.5 × 104 cm–3, with significant diurnal and daily variations, and accounted for ∼89% of the total number concentration (0.01 < d p < 0.43 μm). Time-series plots of the 5-min number concentrations revealed that peak concentrations often occurred during morning rush hour and/or around solar noon when photochemical activity was at a maximum. The morning traffic-related peak coincided with the NO x peak, whereas the photochemical-related peak correlated with solar radiation flux. On some days, the noon peak concentration was many times higher than the morning peak concentration. Although the number size distribution varied considerably over the course of the study, it typically exhibited one to three modes, with diameters around 0.01, 0.05, and 0.09 μm. Analysis of the influence of wind direction indicated that stationary sources could be one of the contributors to elevated ultrafine particle concentration. Overall, the data indicated that fossil fuel combustion and atmospheric gas-to-particle conversion of precursor gases are the major sources of ultrafine particles in the southwest Detroit area during the summer.

Concentration and Size Distribution of Ultrafine Particles Near a Major Highway

Motor vehicle emissions usually constitute the most significant source of ultrafine particles (diameter <0.1 μm) in an urban environment, yet little is known about the concentration and size distribution of ultrafine particles in the vicinity of major highways. In the present study, particle number concentration and size distribution in the size range from 6 to 220 nm were measured by a condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS), respectively. Measurements were taken 30, 60, 90, 150, and 300 m downwind, and 300 m upwind, from Interstate 405 at the Los Angeles National Cemetery. At each sampling location, concentrations of CO, black carbon (BC), and particle mass were also measured by a Dasibi CO monitor, an aethalometer, and a DataRam, respectively. The range of average concentration of CO, BC, total particle number, and mass concentration at 30 m was 1.7−2.2 ppm, 3.4−10.0 μg/m3, 1.3−2.0 × 105/cm3, and 30.2−64.6 μ/m3, respectively. For the conditions of these measurements, relative concentrations of CO, BC, and particle number tracked each other well as distance from the freeway increased. Particle number concentration (6–220 nm) decreased exponentially with downwind distance from the freeway. Data showed that both atmospheric dispersion and coagulation contributed to the rapid decrease in particle number concentration and change in particle size distribution with increasing distance from the freeway. Average traffic flow during the sampling periods was 13,900 vehicles/hr. Ninety-three percent of vehicles were gasoline-powered cars or light trucks. The measured number concentration tracked traffic flow well. Thirty meters downwind from the freeway, three distinct ultrafine modes were observed with geometric mean diameters of 13, 27, and 65 nm. The smallest mode, with a peak concentration of 1.6 × 105/cm3, disappeared at distances greater than 90 m from the freeway. Ultrafine particle number concentration measured 300 m downwind from the freeway was indistinguishable from upwind background concentration. These data may be used to estimate exposure to ultrafine particles in the vicinity of major highways.

Study of ultrafine particles near a major highway with heavy-duty diesel traffic

Motor vehicle emissions usually constitute the most significant source of ultrafine particles (diameter <0.1 μm) in an urban environment. Zhu et al. (J. Air Waste Manage. Assoc., 2002, accepted for publication) conducted systematic measurements of the concentration and size distribution of ultrafine particles in the vicinity of a highway dominated by gasoline vehicle. The present study compares these previous measurements with those made on Interstate 710 freeway in Los Angeles. The 710 freeway was selected because more than 25% of the vehicles are heavy-duty diesel trucks. Particle number concentration and size distribution in the size range from 6 to 220 nm were measured by a condensation particle counter and a scanning mobility particle sizer, respectively. Measurements were taken at 17, 20, 30, 90, 150, and 300 m downwind and 200 m upwind from the center of the freeway. At each sampling location, concentrations of carbon monoxide (CO) and black carbon (BC) were also measured by a Dasibi CO monitor and an Aethalometer, respectively. The range of average concentration of CO, BC and total particle number concentration at 17 m was 1.9–2.6 ppm, 20.3–24.8 μg/m 3, 1.8×10 5–3.5×10 5/cm 3, respectively. Relative concentration of CO, BC and particle number decreased exponentially and tracked each other well as one moves away from the freeway. Both atmospheric dispersion and coagulation appears to contribute to the rapid decrease in particle number concentration and change in particle size distribution with increasing distance from the freeway. Average traffic flow during the sampling periods was 12,180 vehicles/h with more than 25% of vehicles being heavy-duty diesel trucks. Ultrafine particle number concentration measured at 300 m downwind from the freeway was indistinguishable from upwind background concentration. These data may be used to estimate exposure to ultrafine particles in the vicinity of major highways.

Experimental studies of ultrafine particles in streets and the relationship to traffic

Fine and ultrafine particles are of great concern due to their adverse health effects. Furthermore, the emission of ultrafine particles has been reported to be increasing even if the total mass of particles emitted from vehicles decreases. Determination of emission factors of ultrafine particles from the actual car fleet for different types of vehicles is essential for reliable model calculations of the directly emitted particles from the traffic. The present study includes test of measurement methods and analysis of field data from Copenhagen. Measurements of fine and ultrafine particles were carried out during winter/spring 1999, at street level in central Copenhagen, at roof level in Copenhagen, and at street level in the city Odense. The measurements were carried out by differential mobility analyser (DMA) with a high-time resolution corresponding to the variation in traffic and meteorology. The particles were separated into 29 size fractions from 0.01 to 0.7 μm. Significant correlation at street level was observed between the CO, NO x , and ultrafine particles, indicating that the traffic is the major source of ultrafine particles in the air. Time series for several months of the size distributions have been analysed using statistical methods. Factor analysis has been used for the identification of the important sources, and a constrained linear receptor model has been used for source apportionment and for the determination of single-source size distributions of ultrafine particles from diesel- and petrol-fuelled vehicles.

Measurements of mobile source particulate emissions in a highway tunnel

Recent studies have linked atmospheric fine particulate matter (PM2.5) with human health effects. In many urban areas, mobile sources are the dominant source of PM2.5). Dynamometer studies have also implicated diesel engines as being a significant source of ultrafine particles. In order to characterise particulate emissions from in-use vehicles, we performed an on-road study of emissions from vehicles operating in the Tuscarora Mountain Tunnel along the Pennsylvania Turnpike. As part of this study, we obtained chemically speciated, size-segregated PM emission rates, particle size distributions, chemically speciated profiles of diesel emissions for use in source apportionment studies, a comparison with years past how much improvement there has actually been in diesel particulate emission rates, and measurements of particulate emission rates from light-duty gasoline vehicles to evaluate the relative significance of this source. This paper describes the experimental methods and presents the preliminary results of the on-road particulate emissions measurements.

Measurement of number, mass and size distribution of particles in the atmosphere

Typical size distributions for airborne particles are described and the significance of the ultrafine fraction highlighted. Size distributions may be expressed in terms of either mass (volume), surface area or number, and the interpretation of each is discussed together with appropriate measurement methods. The sources of ultrafine particles in the atmosphere include both primary emissions and secondary particles formed through homogeneous nucleation processes within the atmosphere. Examples of measurements of atmospheric ultrafine particles are given, highlighting situations with high concentrations of primary ultrafine particles and also situations where gas–to–particle conversion through homogeneous nucleation gives rise to bursts of new particle production. Finally, the relationship between particle mass and number within the atmosphere at a polluted site is examined.

Ultrafine particles in workplace atmospheres

Inhaled ultrafine particles are increasingly being recognized as a potential threat to health. Aerosols in workplace environments may come from a wide variety of sources, depending on the type of activity and processes taking place. Some activities and processes are acknowledged as being ‘dusty’, where aerosol is generated from the mechanical handling and attrition of solid or liquid material, and are not considered to be plausible sources of ultrafine particles. However, hot processes, involving the vaporization of material, and inevitable subsequent cooling, do have the potential to generate significant number concentrations of ultrafine particles. However, consideration of the physical conditions required for the generation of particles in the range below 100 nm suggests that those conditions are not easily met in workplaces. More generally, the conditions are such that particles grow out of this range, either by continuing condensation (as happens at high vapour concentrations) or by agglomeration between smaller particles (as happens at high number concentrations). Not much is known about ultrafine particles in actual workplaces, mainly because our view has been obscured for the past few decades by the fact that most occupational aerosol standards have been based on the mass concentration of airborne particulate matter. Now that a new awareness has set in, it is expected that new research will address the problem. Most current aerosol standards are expressed in terms of the mass concentration of particulate matter conforming to a particle size fraction, where the latter is based on knowledge of how particle size relates to where particles deposit in the human respiratory tract and any subsequent effects. At present no such basis exists for ultrafine particles, but one is needed before progress can be achieved towards meaningful standards for occupational ultrafine aerosols. It is expected that, for ultrafine particles, such a standard may, in the future, be expressed in terms of the number concentration of particles less than a certain size, that size to be determined on the basis of the physical and chemical nature of the particle at that size, human physiology and toxicology.

Characterization of Indoor Particle Sources Using Continuous Mass and Size Monitors

ABSTRACT A comprehensive indoor particle characterization study was conducted in nine Boston-area homes in 1998 in order to characterize sources of PM in indoor environments. State-of-the-art sampling methodologies were used to obtain continuous PM2.5 concentration and size distribution particulate data for both indoor and outdoor air. Study homes, five of which were sampled during two seasons, were monitored over week-long periods. Among other data collected during the extensive monitoring efforts were 24hr elemental/organic carbon (EC/OC) particulate data as well as semi-continuous air exchange rates and time-activity information. This rich data set shows that indoor particle events tend to be brief, intermittent, and highly variable, thus requiring the use of continuous instrumentation for their characterization. In addition to dramatically increasing indoor PM25 concentrations, these data demonstrate that indoor particle events can significantly alter the size distribution and composition of indoor particles. Source event data demonstrate that the impacts of indoor activities are especially pronounced in the ultrafine (da < 0.1 um) and coarse (2.5 < da < 10 |um) modes. Among the sources of ultrafine particles characterized in this study are indoor ozone/terpene reactions. Furthermore, EC/OC data suggest that organic carbon is a major constituent of particles emitted during indoor source events. Whether exposures to indoor-generated particles, particularly from large short-term peak events, may be associated with adverse health effects will become clearer when biological mechanisms are better known.

Real-time monitoring of particles, PAH, and CO in an occupied townhouse.

Beginning in October 1996, indoor and sometimes outdoor air at an occupied house in a suburban area of Virginia has been monitored continuously for particles, PAH, and CO. Two Climet monitors have been used to count particles in six size ranges between 0.3 and > 10 microns, with 1-minute averages being collected every 5 minutes. Two Ecochem PAH monitors have been used to sample for particle-bound PAHs once every minute. Also, two Langan CO monitor-data loggers have measured CO once each minute while logging the PAH data. Two Aethalometers measure black carbon. A single Scanning Mobility Particle Sizer (SMPS) measures ultrafine particles. The pairs of monitors are set up either to provide an indoor/outdoor or an upstairs office/downstairs kitchen comparison. Air exchange is occasionally measured using a Bruel & Kjaer 1302 SF6 monitor, as a parameter necessary for estimating deposition rates for particles and PAH. Results from the first 16 months of monitoring (approximately 10 M observations) include: neighborhood woodburning and morning rush hour traffic are the most important sources of PAH and black carbon outdoors; candles, matches, incense, and frying, sauteeing, broiling, deep-frying, and stir-frying are additional important indoor sources of PM. One citronella candle was an extremely powerful PAH source. Neither woodburning nor vehicles appears to be an important source of particles indoors, but frying, grilling, and sauteeing are extremely strong indoor sources, together with combustion events such as use of matches and candles. Physical movement was an important source of coarse but not fine particles. Use of the gas stove for extended periods of time led to increased CO concentrations--vehicles and woodburning were relatively minor sources in comparison. The gas oven, gas burners, and electric toaster oven were important sources of ultrafine particles (< 0.1 micron). A source-proximity effect was noted with the kitchen monitor reading two to five times higher than the upstairs monitor for particles from kitchen events, while the upstairs monitor often read higher than the kitchen monitor for events caused by physical activity alone.

Measurements of ultrafine particle concentration and size distribution in the urban atmosphere

Particle size distributions were measured at three adjacent sites in Birmingham: a busy roadside (A38); 30 m away from the road and a nearby urban background site. Two scanning mobility particle sizers (SMPS), an electrical low pressure impactor (ELPI), a condensation particle counter and a thermophoretic precipitator were employed to measure and collect particles. Excellent agreement on the number weighted size distribution was found between the SMPS and ELPI, as well as with sizes measured by transmission electron microscopy. The average number concentration at roadside measured on four separate days was between 1.6 and 1.9×10 5 cm −3 with similar size distributions and more than half of measured particles smaller than 30 nm. Traffic was the main source of ultrafine particles at the roadside. A 24-h average of 2.68×10 4±1.29×10 4 cm −3 was measured, which is close to that in Hughes et al. (Physical and chemical characterization of atmospheric ultrafine particles in the Los Angeles area. Environ Sci Technol 1998; 32:1153–1161) in Pasadena, CA, USA. Total particle number concentration declined downwind of the traffic, faster than the mass concentration. Model calculations show that dilution with background air is the main mechanism for the rapid drop in particle number concentration and change in particle size distribution when moving away from traffic.

Comprehensive characterization of aerosols in a subtropical urban atmosphere: particle size distribution and correlation with gaseous pollutants

This paper presents results of two years of monitoring and research on urban particulates with a focus on submicrometer particles, conducted as a part of an ongoing program on comprehensive characterization of fine airborne particulates and their effect on environmental and human exposures. A large number of data has been collected by the Air Monitoring and Research Station operating in the centre of the subtropical city of Brisbane. The Station is equipped in instrumentation for measurements of particle size distributions in submicrometer and supermicrometer ranges in addition to the standard instrumentation for monitoring of the criteria pollutants (PM 10, ozone, sulphur dioxide, nitrogen oxides and carbon monoxide). The focus of this paper is on presenting results related to characterization of particle size distribution and concentration trends in the study period, correlation between particle characteristics measured by different instruments, correlation between particle and gaseous data and preliminary conclusions on source characteristics and source contribution for the investigated area. The average submicrometer particulate concentration in the study period was 7.4×10 3 particles cm -3, and the average number median diameter was 40 nm. The best correlated data are those for submicrometer particles and carbon monoxide and nitrogen oxides, suggesting the same source type. The lack of correlation between submicrometer and supermicrometer particle concentration data implies different sources for particles in these two ranges. Particle spectral analysis and correlation with gaseous data, indicate that motor vehicle emissions constitute the main source of ultrafine particles in the study area.