UFP Concentrations Research Articles

A review of commuter exposure to ultrafine particles and its health effects

Ultrafine particles (UFPs, <100. nm) are produced in large quantities by vehicular combustion and are implicated in causing several adverse human health effects. Recent work has suggested that a large proportion of daily UFP exposure may occur during commuting. However, the determinants, variability and transport mode-dependence of such exposure are not well-understood. The aim of this review was to address these knowledge gaps by distilling the results of 'in-transit' UFP exposure studies performed to-date, including studies of health effects.We identified 47 exposure studies performed across 6 transport modes: automobile, bicycle, bus, ferry, rail and walking. These encompassed approximately 3000 individual trips where UFP concentrations were measured. After weighting mean UFP concentrations by the number of trips in which they were collected, we found overall mean UFP concentrations of 3.4, 4.2, 4.5, 4.7, 4.9 and 5.7×10 4particlescm -3 for the bicycle, bus, automobile, rail, walking and ferry modes, respectively. The mean concentration inside automobiles travelling through tunnels was 3.0×10 5particlescm -3.While the mean concentrations were indicative of general trends, we found that the determinants of exposure (meteorology, traffic parameters, route, fuel type, exhaust treatment technologies, cabin ventilation, filtration, deposition, UFP penetration) exhibited marked variability and mode-dependence, such that it is not necessarily appropriate to rank modes in order of exposure without detailed consideration of these factors. Ten in-transit health effects studies have been conducted and their results indicate that UFP exposure during commuting can elicit acute effects in both healthy and health-compromised individuals. We suggest that future work should focus on further defining the contribution of in-transit UFP exposure to total UFP exposure, exploring its specific health effects and investigating exposures in the developing world.

Modeling Spatial Patterns of Traffic-Related Air Pollutants in Complex Urban Terrain

BackgroundThe relationship between traffic emissions and mobile-source air pollutant concentrations is highly variable over space and time and therefore difficult to model accurately, especially in urban settings with complex terrain. Regression-based approaches using continuous real-time mobile measurements may be able to characterize spatiotemporal variability in traffic-related pollutant concentrations but require methods to incorporate temporally varying meteorology and source strength in a physically interpretable fashion.ObjectiveWe developed a statistical model to assess the joint impact of both meteorology and traffic on measured concentrations of mobile-source air pollutants over space and time.MethodsIn this study, traffic-related air pollutants were continuously measured in the Williamsburg neighborhood of Brooklyn, New York (USA), which is affected by traffic on a large bridge and major highway. One-minute average concentrations of ultrafine particulate matter (UFP), fine particulate matter [≤ 2.5 μm in aerodynamic diameter (PM2.5)], and particle-bound polycyclic aromatic hydrocarbons were measured using a mobile-monitoring protocol. Regression modeling approaches to quantify the influence of meteorology, traffic volume, and proximity to major roadways on pollutant concentrations were used. These models incorporated techniques to capture spatial variability, long- and short-term temporal trends, and multiple sources.ResultsWe observed spatial heterogeneity of both UFP and PM2.5 concentrations. A variety of statistical methods consistently found a 15–20% decrease in UFP concentrations within the first 100 m from each of the two major roadways. For PM2.5, temporal variability dominated spatial variability, but we observed a consistent linear decrease in concentrations from the roadways.ConclusionsThe combination of mobile monitoring and regression analysis was able to quantify local source contributions relative to background while accounting for physically interpretable parameters. Our results provide insight into urban exposure gradients.

Real Time, Size-resolved Prediction of Ultrafine and Accumulation-mode Particle Concentrations on Freeways

S-31B2-1 Background/Aims: Because on-freeway concentrations of ultrafine particles (UFP; diameter <100 nm) are relatively high, time spent on freeways can be a significant fraction of total daily UFP exposure. Here, we model size-resolved concentrations of UFP and some accumulation-mode particles (size: 100–600 nm) in freeway air. Methods: Our approach is analogous to land-use regression, but using real-time meteorological data (temperature, wind speed, humidity) and traffic data (traffic speed and volume, derived from in-roadway loop detectors). Size-resolved particle concentrations (size: 5.5–600 nm) were measured on Minnesota freeways during the summers of 2006 and 2007. The modeling involves 2-way stratified multi-regressions. Results: Meteorological parameters play only a minor role in predicting real-time UFP concentrations on freeways; traffic speed and volume play a major role. Our regression model for particle number concentration has an adjusted R2 of 0.77. Model performance is better for UFP (size: 10–100 nm; adjusted R2: 0.79–0.89, average R2: 0.85) than for the accumulation-mode particles studied here (size: 100–600 nm; adjusted R2: 0.41–0.83, average R2: 0.65). Conclusion: Our model estimates real-time, size-resolved concentrations of particles (size: 5.5–600 nm) on freeways. The approach developed here is useful for identifying hotspots and as an important step toward modeling population exposure to UFP.

Ultrafine particle penetration through idealized vehicle cracks

Understanding the in-cabin microenvironment of vehicles is important for assessing human exposure to ultrafine particles (UFPs, diameter <100 nm) of vehicular origin. UFP penetration through cracks on the vehicle envelope is one of the influencing processes that determine the in-cabin UFP concentrations. In this study, penetration factors, calculated as the ratio of the downstream to upstream UFP concentrations across seven idealized cracks, were characterized for different crack sizes under a range of different pressure drops across the cracks. Three types of UFPs (neutralized diesel exhaust particles, unneutralized diesel exhaust particles, and vehicle exhaust particles) were used to investigate the effects of electric charge on penetration factors. Crack length, crack height, and pressure drop across the cracks account for approximately 10%, 5% and 12% of the penetration factor change, respectively. A coefficient “ B”, which presents the ratio of the penetration factor for unneutralized to neutralized diesel particles, was introduced and successfully accounted for the electric charge effect on penetration factors.

Effect of Cabin Ventilation Rate on Ultrafine Particle Exposure Inside Automobiles

We alternately measured on-road and in-vehicle ultrafine (<100 nm) particle (UFP) concentration for 5 passenger vehicles that comprised an age range of 18 years. A range of cabin ventilation settings were assessed during 301 trips through a 4 km road tunnel in Sydney, Australia. Outdoor air flow (ventilation) rates under these settings were quantified on open roads using tracer gas techniques. Significant variability in tunnel trip average median in-cabin/on-road (I/O) UFP ratios was observed (0.08 to approximately 1.0). Based on data spanning all test automobiles and ventilation settings, a positive linear relationship was found between outdoor air flow rate and I/O ratio, with the former accounting for a substantial proportion of variation in the latter (R(2) = 0.81). UFP concentrations recorded in-cabin during tunnel travel were significantly higher than those reported by comparable studies performed on open roadways. A simple mathematical model afforded the ability to predict tunnel trip average in-cabin UFP concentrations with good accuracy. Our data indicate that under certain conditions, in-cabin UFP exposures incurred during tunnel travel may contribute significantly to daily exposure. The UFP exposure of automobile occupants appears strongly related to their choice of ventilation setting and vehicle.

High-Resolution Mobile Monitoring of Carbon Monoxide and Ultrafine Particle Concentrations in a Near-Road Environment

Assessment of near-road air quality is challenging in urban environments that have roadside structures, elevated road sections, or depressed roads that may impact the dispersion of traffic emissions. Vehicles traveling on arterial roadways may also contribute to air pollution spatial variability in urban areas. To characterize the nature of near-road air quality in a complex urban environment, an instrumented all-electric vehicle was deployed to perform high spatial- and temporal-resolution mapping of ultra-fine particles (UFPs, particle diameter <100 nm) and carbon monoxide (CO). Sampling was conducted in areas surrounding a highway in Durham, NC, with multiple repeats of the driving route accomplished within a morning or evening commute time frame. Six different near-road transects were driven, which included features such as noise barriers, vegetation, frontage roads, and densely built houses. Under downwind conditions, median UFP and CO levels in near-road areas located 20–150 m from the highway were a factor of 1.8 and 1.2 higher, respectively, than in areas characterized as urban background. Sampling in multiple near-road neighborhoods during downwind conditions revealed significant variability in absolute UFP and CO concentrations as well as in the rate of concentration attenuation with increasing distance from the highway. During low-speed meandering winds, regional UFP and CO concentrations nearly doubled relative to crosswind conditions; however, near-road UFP levels were still higher than urban background levels by a factor of 1.2, whereas near-road CO concentrations were not significantly different than the urban background.

Measurements of ultrafine particles and other vehicular pollutants inside school buses in South Texas

Increasing evidence has demonstrated toxic effects of vehicular emitted ultrafine particles (UFPs, diameter < 100 nm), with the highest human exposure usually occurring on and near roadways. Children are particularly at risk due to immature respiratory systems and faster breathing rates. In this study, children’s exposure to in-cabin air pollutants, especially UFPs, was measured inside four diesel-powered school buses. Two 1990 and two 2006 model year diesel-powered school buses were selected to represent the age extremes of school buses in service. Each bus was driven on two routine bus runs to study school children’s exposure under different transportation conditions in South Texas. The number concentration and size distribution of UFPs, total particle number concentration, PM 2.5, PM 10, black carbon (BC), CO, and CO 2 levels were monitored inside the buses. The average total particle number concentrations observed inside the school buses ranged from 7.3 × 10 3 to 3.4 × 10 4 particles cm −3, depending on engine age and window position. When the windows were closed, the in-cabin air pollutants were more likely due to the school buses’ self-pollution. The 1990 model year school buses demonstrated much higher air pollutant concentrations than the 2006 model year ones. When the windows were open, the majority of in-cabin air pollutants came from the outside roadway environment with similar pollutant levels observed regardless of engine ages. The highest average UFP concentration was observed at a bus transfer station where approximately 27 idling school buses were queued to load or unload students. Starting-up and idling generated higher air pollutant levels than the driving state. Higher in-cabin air pollutant concentrations were observed when more students were on board.

Comparison of carcinogen, carbon monoxide, and ultrafine particle emissions from narghile waterpipe and cigarette smoking: Sidestream smoke measurements and assessment of second-hand smoke emission factors

The lack of scientific evidence on the constituents, properties, and health effects of second-hand waterpipe smoke has fueled controversy over whether public smoking bans should include the waterpipe. The purpose of this study was to investigate and compare emissions of ultrafine particles (UFP, <100 nm), carcinogenic polyaromatic hydrocarbons (PAH), volatile aldehydes, and carbon monoxide (CO) for cigarettes and narghile (shisha, hookah) waterpipes. These smoke constituents are associated with a variety of cancers, and heart and pulmonary diseases, and span the volatility range found in tobacco smoke. Sidestream cigarette and waterpipe smoke was captured and aged in a 1 m 3 Teflon-coated chamber operating at 1.5 air changes per hour (ACH). The chamber was characterized for particle mass and number surface deposition rates. UFP and CO concentrations were measured online using a fast particle spectrometer (TSI 3090 Engine Exhaust Particle Sizer), and an indoor air quality monitor. Particulate PAH and gaseous volatile aldehydes were captured on glass fiber filters and DNPH-coated SPE cartridges, respectively, and analyzed off-line using GC–MS and HPLC–MS. PAH compounds quantified were the 5- and 6-ring compounds of the EPA priority list. Measured aldehydes consisted of formaldehyde, acetaldehyde, acrolein, methacrolein, and propionaldehyde. We found that a single waterpipe use session emits in the sidestream smoke approximately four times the carcinogenic PAH, four times the volatile aldehydes, and 30 times the CO of a single cigarette. Accounting for exhaled mainstream smoke, and given a habitual smoker smoking rate of 2 cigarettes per hour, during a typical one-hour waterpipe use session a waterpipe smoker likely generates ambient carcinogens and toxicants equivalent to 2–10 cigarette smokers, depending on the compound in question. There is therefore good reason to include waterpipe tobacco smoking in public smoking bans.

On-road ultrafine particle concentration in the M5 East road tunnel, Sydney, Australia

The human health effects following exposure to ultrafine (<100 nm) particles (UFPs) produced by fuel combustion, while not completely understood, are generally regarded as detrimental. Road tunnels have emerged as locations where maximum exposure to these particles may occur for the vehicle occupants using them. This study aimed to quantify and investigate the determinants of UFP concentrations in the 4 km twin-bore (eastbound and westbound) M5 East tunnel in Sydney, Australia. Sampling was undertaken using a condensation particle counter (CPC) mounted in a vehicle traversing both tunnel bores at various times of day from May through July, 2006. Supplementary measurements were conducted in February, 2008. Over three hundred transects of the tunnel were performed, and these were distributed evenly between the bores. Additional comparative measurements were conducted on a mixed route comprising major roads and shorter tunnels, all within Sydney. Individual trip average UFP concentrations in the M5 East tunnel bores ranged from 5.53 × 10 4 p cm −3 to 5.95 × 10 6 p cm −3. Data were sorted by hour of capture, and hourly median trip average (HMA) UFP concentrations ranged from 7.81 × 10 4 p cm −3 to 1.73 × 10 6 p cm −3. Hourly median UFP concentrations measured on the mixed route were between 3.71 × 10 4 p cm −3 and 1.55 × 10 5 p cm −3. Hourly heavy diesel vehicle (HDV) traffic volume was a very good determinant of UFP concentration in the eastbound tunnel bore ( R 2 = 0.87), but much less so in the westbound bore ( R 2 = 0.26). In both bores, the volume of passenger vehicles (i.e. unleaded gasoline-powered vehicles) was a significantly poorer determinant of particle concentration. When compared with similar studies reported previously, the measurements described here were among the highest recorded concentrations, which further highlights the contribution road tunnels may make to the overall UFP exposure of vehicle occupants.

Ultrafine particles near a major roadway in Raleigh, North Carolina: Downwind attenuation and correlation with traffic-related pollutants

Ultrafine particles (UFPs, diameter < 100 nm) and co-emitted pollutants from traffic are a potential health threat to nearby populations. During summertime in Raleigh, North Carolina, UFPs were simultaneously measured upwind and downwind of a major roadway using a spatial matrix of five portable industrial hygiene samplers (measuring total counts of 20–1000 nm particles). While the upper sampling range of the portable samplers extends past the defined “ultrafine” upper limit (100 nm), the 20–1000 nm number counts had high correlation (Pearson R = 0.7–0.9) with UFPs (10–70 nm) measured by a co-located research-grade analyzer and thus appear to be driven by the ultrafine range. Highest UFP concentrations were observed during weekday morning work commutes, with levels at 20 m downwind from the road nearly fivefold higher than at an upwind station. A strong downwind spatial gradient was observed, linearly approximated over the first 100 m as an 8% drop in UFP counts per 10 m distance. This result agreed well with UFP spatial gradients estimated from past studies (ranging 5–12% drop per 10 m). Linear regression of other vehicle-related air pollutants measured in near real-time (10-min averages) against UFPs yielded moderate to high correlation with benzene ( R 2 = 0.76), toluene ( R 2 = 0.49), carbon monoxide ( R 2 = 0.74), nitric oxide ( R 2 = 0.80), and black carbon ( R 2 = 0.65). Overall, these results support the notion that near-road levels of UFPs are heavily influenced by traffic emissions and correlate with other vehicle-produced pollutants, including certain air toxics.

Roadside Measurements of Ultrafine Particles at a Busy Urban Intersection

A field sampling campaign on ultrafine particles (UFPs, diameter <100 nm) was conducted at a busy traffic intersection from December 2006 to June 2007 in Corpus Christi, TX. This traffic intersection consisted of South Padre Island Drive (SPID, Highway 358) and Staples Street. Traffic densities on SPID were 9102/hr and 7880/hr for weekdays and weekends, respectively. Staples Street traffic densities were 2795/hr and 2572/hr, respectively. There were approximately 3.7% heavy-duty diesel vehicles (HDDVs) on both roadways. Peak traffic flows occurred early in the morning and late in the evening during weekdays and around noon on weekends. The average UFP total number concentration collected by a condensation particle counter (CPC 3785; TSI) was 66 × 103 cm−3. A direct relationship between the UFP number concentration and traffic density was observed, but the HDDV traffic density was found to be a better estimator of the UFP number concentration than total traffic density. A scanning mobility particle sizer (SMPS 3936 with DMA 3081 and CPC 3785, TSI) measuring the particle size distribution from 7 to 290 nm was rotated among four corners of the intersection. The upwind and downwind size distributions were both bimodal in shape, exhibiting a nucleation mode at 10 –30 nm and a secondary mode at 50 –70 nm. The highest and lowest particle concentrations were observed on the downwind and upwind sides of both roadways, respectively, indicating the importance of wind direction. Wind speed also played an important role in overall particle concentrations; UFP concentrations were inversely proportional to wind speed. A negative correlation was observed between particle number concentrations and ambient temperature. The particle number concentration was 3.5 times greater when traffic was idling at a red light than moving at a green light.

Exposure to fine and ultrafine particles from secondhand smoke in public places before and after the smoking ban, Italy 2005

Background: A smoking ban in all indoor public places was enforced in Italy on 10 January 2005. Methods: We compared indoor air quality before and after the smoking ban by...

Ambient Ultra-Fine Particles and Children's Exhaled Nitric Oxide in Beijing

ISEE-749 Objective: This study focuses on examining the relationship between UFP and eNO in 17 nonasthmatic children (9–11 years old) from an elementary school located < 1 km from an ambient air monitoring site in Beijing. Materials and Methods: At this site, a Twin Differential Mobility Particle Sizer System and an Aerosol Particle Sizer were used to measure number concentrations of particles in several size ranges starting from 3 nm and up to 10 μm. Particles were measured at 10-min intervals continuously during the study period (October 2005–April 2006). Each child was measured once per day for 30 days. Exhaled breath samples were collected into an aluminum bag and subsequently analyzed for NO using a chemiluminescent NOx-NO2-NO analyzer. In our analysis, we calculated concentrations of UFP (diameter < 100 nm), both averaged over the 24-hour period before each eNO measurement day and the maximum 1-hour moving average within the same 24-hour period. Linear mixed-effects models were used to regress eNO against UFP, along with or without a copollutant (NO2 or SO2), respectively. A repeated statement was used to estimate the covariance effects of residual; and the covariance structure was chosen as compound symmetry. Results: Results showed that UFP concentrations were 25,484.1 ± 7403 cm−3 and eNO concentrations were 9.7 ± 9.0 ppb. Using 24-hour average concentrations, we found an increase in UFP by 10,000 cm−3 was associated with an increase in eNO by 0.56 ppb (P = 0.14), 0.25 ppb (P = 0.47) after adjusting for NO2, and 0.28 ppb (P = 0.38) after adjusting for SO2. Using maximum 1-hour concentrations, we found an increase in UFP by 10,000 cm−3 was associated with an increase in eNO by 0.22 ppb (P = 0.13), 0.19 ppb (P = 0.15) after adjusting for NO2, and 0.21 ppb (P = 0.09) after adjusting for SO2. Conclusions: These findings suggest a positive association between eNO and UFP. More detailed analyses, considering different particle size ranges, seasonal effects, etc, are being undertaken.

Measurements of fine and ultrafine particles formation in photocopy centers in Taiwan

This study investigates the levels of particulate matter smaller than 2.5 μm (PM 2.5) and some selected volatile organic compounds (VOCs) at 12 photocopy centers in Taiwan from November 2004 to June 2005. The results of BTEXS (benzene, toluene, ethylbenzene, xylenes and styrene) measurements indicated that toluene had the highest concentration in all photocopy centers, while the concentration of the other four compounds varied among the 12 photocopy centers. The average background-corrected eight-hour PM 2.5 in the 12 photocopy centers ranged from 10 to 83 μg m −3 with an average of 40 μg m −3. The 24-h indoor PM 2.5 at the photocopy centers was estimated and at two photocopy centers exceeded 100 μg m −3, the 24-h indoor PM 2.5 guideline recommended by the Taiwan EPA. The ozone level and particle size distribution at another photocopy center were monitored and indicated that the ozone level increased when the photocopying started and the average ozone level at some photocopy centers during business hour may exceed the value (50 ppb) recommended by the Taiwan EPA. The particle size distribution monitored during photocopying indicated that the emitted particles were much smaller than the original toner powders. Additionally, the number concentration of particles that were smaller than 0.5 μm was found to increase during the first hour of photocopying and it increased as the particle size decreased. The ultrafine particle (UFP, <100 nm) dominated the number concentration and the peak concentration appeared at sizes of under 50 nm. A high number concentration of UFP was found with a peak value of 1E+8 particles cm −3 during photocopying. The decline of UFP concentration was observed after the first hour and the decline is likely attributable to the surface deposition of charged particles, which are charged primarily by the diffusion charging of corona devices in the photocopier. This study concludes that ozone and UFP concentrations in photocopy centers should be concerned in view of indoor air quality and human health. The corona devices in photocopiers and photocopier-emitted VOCs have the potential to initiate indoor air chemistry during photocopying and result in the formation of UFP.

Runs of Ventricular and Supraventricular Tachycardia Triggered by Air Pollution in Patients with Coronary Heart Disease

The authors conducted an investigation of the association between air pollution and arrhythmia. A prospective panel study (October 2000-April 2001) was conducted in Erfurt, Germany. Fifty-seven men with coronary heart disease were subjected to six 24-hour electrocardiogram recordings. Runs of supraventricular and ventricular tachycardia were associated with continuous ultrafine particle counts (UFP), accumulation mode particle counts (ACP), PM2.5, and gaseous pollutants. Poisson and linear regression models were applied adjusting for trend, weekday, and meteorologic data. Elevated concentrations of UFP, ACP, PM2.5, and nitrogen dioxide increased the risk for supraventricular runs and the number of ventricular runs at almost all lags. Statistically significant associations were found predominantly in the previous 24 to 71 hours and with the 5-day moving average. Elevated concentrations of fine and ultrafine particle increased the risk of arrhythmia in men with coronary heart disease.

Particle Characteristics in the Reactor and Pelletizing Areas of Carbon Black Production

Physical and chemical characteristics of airborne particles (ultrafine, PM1 , PM 2.5, and PM 10) in reactor and pelletizing areas during carbon black production were measured to assess process related sources of particles in work areas. Results from bagging areas within the same three facilities have been previously published. Particle number and mass concentration measurements were conducted in these work areas and at ambient comparison sites at each of the three carbon black plants. No elevated ultrafine particle number concentrations (UFP, <100 nm) with respect to ambient were determined in the work areas of Plant 1, intermittently elevated concentrations at Plant 2, and permanently elevated concentrations at Plant 3. The intermittently elevated UFP concentrations in the pelletizer and reactor areas of Plant 2 could be related to nearby traffic emissions. The ultrafine particle number concentrations at Plant 2 are comparable to those determined at urban traffic sites. Both work areas of Plant 3 showed elevated UFP concentrations in the pelletizer reactor and areas. In the case of the reactor, which was the only enclosed reactor area investigated among the three facilities, the source of the elevated UFP number concentration was most likely attributable to grease and oil fumes from maintenance activities, a conclusion supported by carbon fractionation analysis. The elevated UFP number concentrations in the pelletizing area in this same plant are related to leaks in the production line, which allowed particulate matter to escape to the surrounding areas. Absolute PM10 mass concentrations were all within normal ambient concentrations except for the pelletizing area in Plant 3, which showed continuous levels above ambient. One additional source contributing to peak level PM10 mass concentrations at Plant 2 was due to wind dispersion from a carbon black spill incident the day prior to measurements. It is concluded from these measurements that no carbon black is released in the reactor and pelletizing areas (as UFP or PM10) from the closed production lines under normal operating conditions.

HEALTH EFFECTS OF DIESEL EXHAUST IN ASTHMATIC PATIENTS: A REAL-WORLD STUDY IN LONDON

ISEE-210 Introduction: Epidemiological evidence suggests a link between respiratory morbidity and urban fine particulates, many of which are produced by diesel-powered vehicles. Aim: We studied the direct health effects of diesel exhaust on humans exposed within a ‘natural chamber’. Methods: On separate occasions, non-smoking adult asthmatics were exposed, for 2 hours, in Oxford Street, London (where only pedestrians, diesel powered buses and taxicabs are permitted) or Hyde Park, a large, nearby open park free of vehicles. We measured PM 2.5, elemental carbon, NO2 and ultrafine particulates during each session. Lung function and symptoms were monitored during exposures and for 24 hours after. Results: Measurements showed daytime concentrations of elemental carbon (EC) on Oxford Street are approximately 5 times higher than in Hyde Park. There were significant differences in measured concentrations of particulate pollution between exposure sites (UFP concentration (gravimetric mean). Initial analyses showed that the lung function (FEV1 and FVC) decreased from baseline at both exposure sites; this decrement was largest and more sustained following active exposure. Active exposure was also associated with increased symptoms. Conclusion: Initial analyses of this study suggests that asthmatic subjects exposed to ambient urban levels of diesel exhaust, in a natural environment, incur worsening respiratory function and symptoms that increase as particulate concentrations rise.

Indoor and outdoor particle size characterization at a family house in Espoo–Finland

Aerosol particle number size distributions (3–400 nm) were measured for three weeks both indoors and outdoors in a family house with natural ventilation in Espoo, Finland. We investigated the indoor-to-outdoor relationship of aerosol particles and analyzed the effects of indoor activities on the particle number size distributions. We also estimated the decay rate of indoor aerosol particle number concentrations. As expected, in the absence of indoor sources of aerosol particles the indoor particles originated from outdoors and the number concentrations followed similar patterns as those outdoors. The maximum penetration was found for particles between 100 and 400 nm in diameter. The mean value of the I/O values was 0.36 for ultrafine particles (UFP diameter <100 nm) and 0.60 for particles larger than 100 nm in diameter. Because of the penetration and deposition processes of aerosol particles, the modal structure of indoor particle number size distributions had larger geometric mean diameters and significantly lower number concentrations of UFP than those outdoors. The natural ventilation did not provide a stable and controlled indoor-to-outdoor relationship of aerosol particles and it caused variable I/O values and time-lags (10–45 min). In the presence of indoor activities, the indoor particle number concentrations cannot be directly estimated from the outdoor number concentrations only. The loss rate of UFP in the indoor air ranged from 1 h−1 for 10 nm particles to 0.1 h−1 for 100 nm particles in diameter. The quantitative and qualitative results presented in the current study are building and condition specific. However, the results provide a better understanding of the particle number size distribution characterizations indoors, especially during different indoor activities.

Indoor and outdoor concentrations of ultrafine particles in some Scandinavian rural and urban areas

The concentration of ultrafine particles (0.01 to greater than 1 μm) was measured in some rural and urban areas of Sweden and Denmark. The instruments used are handheld real-time condensation particle counters, models CPC 3007 and P-Trak™ 8525, both manufactured by TSI. Field measurements in Sweden were conducted in a few residential and office buildings, while in Denmark the measurement sites comprised two office buildings, one of them located in a rural area. The concentration of UFPs was measured simultaneously indoors and outdoors with condensation particle counters. The results revealed that the outdoor-generated particle levels were major contributors to the indoor particle number concentration in the studied buildings when no strong internal source was present. The results showed that in office buildings, the UFP concentrations indoors were typically lower and correlated fairly well to the number concentration outdoors. The determined indoor-outdoor ratios varied between 0.5 and 0.8. The indoor levels of UFPs in offices where smoking is allowed was sometimes recorded higher than outdoor levels, as in one of the Danish offices. In residential buildings, the indoor number concentration was strongly influenced by several indoor activities, e.g., cooking and candle burning. In the presence of significant indoor sources, the indoor/outdoor (IO) ratio exceeded unity. The magnitude of UFP concentrations was greater in the large city of Copenhagen compared to the medium-size city of Gothenburg and lowest at more rural sites.

Characteristics of Nucleation and Growth Events of Ultrafine Particles Measured in Rochester, NY

Number concentrations and size distributions of particles in the size range of 0.010-0.500 microm were measured in Rochester, NY, from December 2001 to December 2002. The relationships between the number concentrations, gaseous pollutants, and meteorological parameters were examined during particle nucleation events. More than 70% of measured total number concentration was associated with ultrafine particles (UFP, 0.011-0.050 microm). Morning nucleation events typically peaking UFP number concentrations at around 08:00 were apparent in winter months with CO increases. These particles appear to be formed following direct emissions from motorvehicles during morning rush hour. There were also often observed increases in this smaller-sized range particles in the late afternoon during the afternoon rush hour, particularly in winter when the mixing heights remain lowerthan in summer. Strong afternoon nucleation events (> 30,000 cm(-3)) peaking at around 13: 00 were more likely to occur in spiring and summer months. During the prominent nucleation events, peaks of SO2 were strongly associated with the number concentrations of UFP, whereas there were no significant correlations between these events and PM2.5 and CO. Increased SO2 concentrations were observed when the wind direction was northwesterly where three SO2 sources were located. It is hypothesized that UFP formed during the events are sulfuric acid and water from the oxidation of SO2. There were also a more limited number of nucleation events followed by particle growth up to approximately 0.1 microm over periods of up to 18 h. The nucleation and growth events tended to be common in spring months especially in April.