Associations between particle number and gaseous co-pollutant concentrations in the Los Angeles Basin

Continuous measurements of particle number (PN), particle mass (PM10), and gaseous pollutants [carbon monoxide (CO), nitric oxide (NO), oxides of nitrogen (NOx), and ozone (O3)] were performed at five urban sites in the Los Angeles Basin to support the University of Southern California Children's Health Study in 2002. The degree of correlation between hourly PN and concentrations of CO, NO, and nitrogen dioxide (NO2) at each site over the entire year was generally low to moderate (r values in the range of 0.1-0.5), with a few notable exceptions. In general, associations between PN and O3 were either negative or insignificant. Similar analyses of seasonal data resulted in levels of correlation with large variation, ranging from 0.0 to 0.94 depending on site and season. Summertime data showed a generally higher correlation between the 24-hr average PN concentrations and CO, NO, and NO2 than corresponding hourly concentrations. Hourly correlations between PN and both CO and NO were strengthened during morning rush-hour periods, indicating a common vehicular source. Comparing hourly particle number concentrations between sites also showed low to moderate spatial correlations, with most correlation coefficients below 0.4. Given the low to moderate associations found in this study, gaseous co-pollutants should not be used as surrogates to assess human exposure to airborne particle number concentrations.     

Relationships between size segregated mass concentration data and ultrafine particle number concentrations in urban areas

Mass concentration data derived from samples collected with a micro-orifice uniform deposit impactor (MOUDI) in six Australian urban centers during periods of significant particle loading have been used to investigate the relationships between TSP, PM10, PM2.5, PM1 and ultrafine particles. While PM10 and PM2.5 display a clear relationship, the lack of correlation between PM10 and the coarse fraction of PM10 (PM10–PM2.5) suggests that variation in PM10 is dominated by variance in PM2.5. Given that particles of less than 2.5 μm are suspected to have adverse health effects, increasing the extent of PM2.5 monitoring may improve detection of relationships between air pollution and human health. A lack of correlation between both PM10 and PM2.5 with ultrafine mass concentrations indicates that PM10 and PM2.5 cannot be used as a surrogate for ultrafine mass concentration. Similarly, ultrafine number concentrations cannot be inferred from mass concentration information determined by the MOUDI.     

Some insights into short-term variability of total gaseous mercury in urban air

The concentrations of total gaseous mercury (Hg) were determined at hourly intervals along with relevant environmental parameters that include both meteorological plus criteria pollutant data during two field campaigns (September 1997 and May/June 1998). The mean concentrations of Hg for the two study periods were computed as 3.94 and 3.43 ng m⁻³, respectively. By separating the data into daytime and nighttime periods, we further analyzed diurnal variation patterns for both seasons. Using our Hg data sets, we were able to recognize two contrasting diurnal variation patterns of Hg between two different seasons that can be characterized as: (1) the occurrences of peak Hg concentration during daytime (fall) and (2) slight reductions in daytime Hg concentration relative to nighttime (summer). To study the systematic differences in diurnal patterns between two different seasons, we analyzed Hg data in terms of different statistical approaches such as correlation (and linear regression) and factor analysis. Results of these analyses consistently indicated that different mechanisms were responsible for controlling the daytime distribution patterns of Hg. When the relationship between Hg and concurrently determined O₃ is considered, its reaction with ozone is unlikely to limit Hg levels as the dominant sink mechanism (within the ranges of ozone concentrations found during this study, regardless of season). It is on the other hand suspected that the variation of boundary layer conditions between day/night periods may have been important in introducing the relative reduction in daytime Hg levels during summer. To further provide a general account of short-term variations in Hg distribution data, it is desirable to describe other unknown sink mechanisms.     

The co-occurrence of potentially phytotoxic concentrations of various gaseous air pollutants

Studies on impacts of air pollutants on vegetation have focused primarily on individual pollutants: ozone, sulfur dioxide and nitrogen dioxide. The impacts of pollutant combinations have not been extensively studied and there has been no concerted effort to ensure that experimental regimes for combined pollutant exposures are representative of ambient pollutant concentration, frequency, duration and time intervals between events. Most studies concerning the impact of pollutant combinations on vegetation have used concentrations of 0.05 ppm and greater. Therefore, co-occurrence was defined as the simultaneous occurrence of hourly averaged concentrations of 0.05 ppm or greater for pollutant pairs (SO₂/NO₂, O₃/SO₂, or O₃/NO₂). Air quality information from three data bases (EPA-SAROAD, EPRI-SURE and TVA) was analyzed to determine the frequency of co-occurrence for pollutant pairs. Ambient air quality data representing a diverse range of monitoring sites (e.g. rural, remote, city center, urban, near urban, etc.) were used in the analysis. Results showed that at most sites (1) the co-occurrence of two-pollutant mixtures lasted only a few hours per episode, (2) the time interval between episodes was generally large (weeks, sometimes months) and (3) most studies have used more intense exposure regimes than occurred at most monitored sites. When designing vegetation experiments for assessing pollutant mixture effects, it may be desirable to give greater emphasis to sequential patterns of exposure. It is suggested that future work is required before a reliable estimate can be made of the environmental significance of pollutant mixtures on vegetation.     

Controls on hourly variations in urban background air pollutant concentrations

Average 21st century concentrations of urban air pollutants linked to cardiorespiratory disease are not declining, and commonly exceed legal limits. Even below such limits, health effects are being observed and may be related to transient daytime peaks in pollutant concentrations. With this in mind, we analyse >52,000 hourly urban background readings of PM₁₀ and pollutant gases throughout 2007 at a European town with legal annual average concentrations of common pollutants, but with a documented air pollution-related cardiorespiratory health problem, and demonstrate the hourly variations in PM₁₀, SO₂, NO_x, CO and O₃. Back-trajectory analysis was applied to track the arrival of exotic PM₁₀ intrusions, the main controls on air pollutants were identified, and the typical hourly pattern on ambient concentrations during 2007 was profiled. Emphasis was placed on “worst case” data (>90th percentile), when health effects are likely to be greatest. The data show marked daytime variations in pollutants result from rush-hour traffic-related pollution spikes, midday industrial SO₂ maxima, and afternoon O₃ peaks. African dust intrusions enhance PM₁₀ levels at whatever hour, whereas European PM incursions produce pronounced evening peaks due to their transport direction (across an industrial traffic corridor). Transient peak profiling moves us closer to the reality of personal outdoor exposure to inhalable pollutants in a given urban area. We argue that such an approach to monitoring data potentially offers more to air pollution health effect studies than using only 24 h or annual averages.     

Regional transport and urban contributions to fine particle concentrations in southeastern Canada

The impact of various atmospheric transport directions on ambient fine particle (PM2.5) concentrations at several sites in southeastern Canada was estimated (for May-September) using back-trajectory analysis. Three-day back trajectories (four per day) were paired with 6-hr average PM2.5 mass concentrations measured using tapered element oscillating microbalances (TEOM). PM2.5 concentrations at rural locations in the region were affected by nonlocal sources originating in both Canada and the United States. Comparison of sites revealed that, on average, the local contribution to total PM2.5 in the greater Toronto area (GTA) is approximately 30-35%. At each location, average PM2.5 concentrations under south/southwesterly flow conditions were 2-4 times higher than under the corresponding northerly flow conditions. The chemical composition of both urban and rural PM2.5 was determined during two separate 2-week spring/summer measurement campaigns. Components identified included SO4(2-) NO3-, NH4+, black carbon and organic carbon (OC), and trace elements. Higher particle mass at the urban Toronto site was composed of a higher proportion of all components. However, black carbon, NO3-, NaCl, and trace elements were found to be the most enriched over the rural/regional background levels.     

Relation between particle mass and number for submicrometer airborne particles

The relationship between particle mass and the number of ambient air particles for the submicrometer size range was examined using a tapered element oscillating microbalance (TEOM) to determine the mass concentration, and a scan-ning mobility particle sizer (SMPS) to determine the volume concentration and total number of particles. The techniques were validated through their application to the estimation of submicrometer particle density for two laboratory generated aerosols of known bulk density (sodium chloride and di-2-ethylhexyl-sebacate). Further evaluation was done with the submicrometer fraction of laboratory generated environmental tobacco smoke (ETS), for which the estimated density of 1.18±0.06 g/cm³ was very close to the previously reported literature value of 1.12 g cm³. Finally, ambient air particles were examined and an estimate of the average submicrometer particle densities for these aerosols was found to vary from 1.2 to 1.8 g cm^-3 depending on the time of day. This high variation in the density of the ambient air submicrometer particles, makes it hard to estimate the mass concentration from the SMPS number concentration with better than 60% uncertainty, based on an assumed density value.     

Co-occurrence patterns of gaseous air pollutant pairs at different minimum concentrations in the United States

The frequency of co-occurrences for SO₂NO₂, SO₂/O₃ and O₃/NO₂ at rural and remote monitoring sites in the United States was characterized for the months of May-September for the years 1978–1982. Minimum hourly concentrations of 0.03 and 0.05 ppm of each gas were used as the criteria for defining a ‘co-occurrence’. The objectives of this study were to:

• 1.(1) identify the types of co-occurrence patterns and their frequency;
• 2.(2) identify whether the frequency of hourly simultaneous co-occurrences increased substantially when the minimum concentration was lowered (e.g. from 0.05 to 0.03 ppm) for each pollutant; and
• 3.(3) determine whether the frequency of co-occurrences showed large year-to-year variation.

For all pollutant pairs and co-occurrence thresholds (i.e. 0.03 and 0.05 ppm), the frequency of daily and hourly co-occurrences was low for most sites. Year-to-year variability was found to be insignificant; most of the monitoring sites experienced co-occurrences of any type less than 12% of the 153 days. Based on our observations, researchers attempting to assess the potential effects of SO₂/NO₂, SO₂/O₃ and O₃/NO₂ in the United States should construct simulated exposure regimes so that

• 1.(1) hourly simultaneous and daily simultaneous-only co-occurrences are fairly rare and
• 2.(2) when co-occurrences are present, complex-sequential and sequential-only co-occurrence patterns predominate.

     

Street level versus rooftop concentrations of submicron aerosol particles and gaseous pollutants in an urban street canyon

Gaseous air pollutants and aerosol particle concentrations were monitored in an urban street canyon for two weeks. The measurements were performed simultaneously at two different heights: at street level (gases 3 m, aerosol particles 1.5 m) and at a rooftop 25 m above the ground. The main objective of the study was to investigate the vertical changes in concentrations of pollutants and the factors leading to the formation of the differences. The physical parameters controlling the concentration gradients (e.g. the flow and micrometeorology) were not directly measured and the conclusions of the study rely mostly on the high time resolution concentration measurements. It was concluded that dilution and dispersion decreases the concentrations of pollutants emitted at street level by a factor of roughly 5 between the two sampling heights. However, for some compounds the chemical reactions were seen to be of more importance when the vertical gradient is formed. In order to determine the processes leading to gradients in aerosol particle concentrations the photochemical formation of submicrometer aerosol particles was investigated using a theoretical expression based on the measured data. It was clearly seen that most of the particles originate from traffic in the vicinity of the measurement site. Also a few events were detected which might have been due to local gas-to-particle conversion.     

Difference in concentration trends of airborne particulate matter during rush hour on weekdays and Sundays in Tokyo,Japan

Suspended particulate matter (SPM) and fine particulate matter (less than or equal to 2.5 μm: PM_2.5) have generally been decreasing for the last decade in Tokyo, Japan. To elucidate the major cause of this decrease, the authors investigated the different trends of airborne particulates (both SPM and PM_2.5 concentrations) by evaluating comparisons based on the location of the monitoring stations (roadside vs. ambient), days of the week (weekdays vs. Sundays), and daily fluctuation patterns (2002 vs. 2010). Hourly mean SPM and PM_2.5 concentrations were obtained at four monitoring stations (two roadside stations, two ambient stations) in Tokyo, Japan. Annual mean concentrations of each day of the week and of each hour of the day from 2002 to 2010 were calculated. The results showed that (1) the daily differences in annual mean concentration decreased only at the two roadside monitoring stations; (2) the high hourly mean concentrations observed on weekdays during the daily rush hour at the two roadside monitoring stations observed in 2002 diminished in 2010; (3) the SPM concentration that decreased the most since 2002 was the PM_2.5 concentration; and (4) the fluctuation of hourly concentrations during weekdays at the two roadside monitoring stations decreased. A decreasing trend of airborne particulates during the daily rush hour in Tokyo, Japan, was observed at the roadside monitoring stations on weekdays since 2002. The decreasing PM_2.5 concentration resulted in this decreasing trend of airborne particulate concentrations during the daily rush hours on weekdays, which indicates fewer emissions were produced by diesel vehicles.

ImplicationsThe authors compared the trends of SPM and PM_2.5 in Tokyo by location (roadside vs. ambient), days of the week (weekdays vs. Sundays), and daily fluctuation patterns (2002 vs. 2010). The high hourly mean concentrations observed at the roadside location during rush hour on weekdays in 2002 diminished in 2010. The SPM concentration that decreased during rush hour the most was the PM_2.5 concentration. This significant decrease in the PM_2.5 concentration resulted in the general decreasing trend of SPM concentrations during the rush hours on weekdays, which indicates fewer emissions were produced from diesel vehicles.     

Differences between weekday and weekend air pollutant levels in southern California

Ambient air quality data were analyzed to empirically evaluate the effects of reductions of volatile organic compounds (VOCs) and oxides of nitrogen (NOx) emissions on weekday and weekend levels of ozone (O3; 1991-1998) and particulate NO3- (1980-1999) in southern California. Despite significantly lower O3 precursor levels on weekends, 20 of 28 South Coast Air Basin (SoCAB) sites (28 of all 78 southern California sites) showed statistically significant higher mean O3 levels on Sundays than on weekdays (p < 0.01); 49 of the remaining 50 sites showed no significant differences between mean weekday and Sunday peak O3 levels. We also observed no statistically significant differences between mean weekday and weekend concentrations of particulate NO3- or nitric acid (HNO3, the precursor of particulate NO3-). Averaged over sites, the mean Sunday NOx and nonmethane hydrocarbon concentrations were 25-41% and 16-30% lower, respectively, than on weekdays. Site-to-site differences between weekend and weekday mean peak hourly O3 levels were related to whether O3 formation was limited by the availability of NOx. A thermodynamic equilibrium model predicts that particulate NO3- levels would decrease in response to a reduction of HNO3, and that particulate ammonium NO3- formation was not limited by the availability of ammonia. The similarity of mean weekday and weekend levels of NO3- therefore did not result from limitations on the formation of particulate NO3- from its precursor, HNO3.     

Simultaneous absolute measurements of gaseous nitrogen species in urban ambient air by long pathlength infrared and ultraviolet-visible spectroscopy

Two new long pathlength spectrometers, utilizing 25-m basepath multiple reflection optical systems, were employed for the first time during an intercomparison of measurement methods for atmospheric nitrogenous species held at Claremont, CA, 11–19 September 1985. Measurement of nitrogenous species using these closed optical path systems, as opposed to single pass systems extending several kilometers, permit the resulting in situ absolute spectroscopic data to serve as benchmark values for point monitors employing denuders or filter packs. The FT-IR spectrometer was operated at a total pathlength of 1150 m and spectral resolution of 0.125 cm⁻¹, with corresponding detection sensitivities of 160 nmolem⁻³ for HNO₃ and 60 nmole m⁻³ for NH₃ (4 and 1.5 ppb, respectively). Concurrent measurements of HONO, NO₂ and NO₃ radicals were conducted with the differential optical absorption spectrometer operated at 800 m total pathlength with detection limits of 24, 160 and 0.8 nmole m⁻³ (0.6, 4 and 0.02 ppb) for HONO, NO₂, and NO₃ radicals, respectively.     

Effects of ceiling-mounted HEPA-UV air filters on airborne bacteria concentrations in an indoor therapy pool building

The purpose of this study was to assess the effectiveness of a new generation of high-volume, ceiling-mounted high-efficiency particulate air (HEPA)-ultraviolet (UV) air filters (HUVAFs) for their ability to remove or inactivate bacterial aerosol. In an environmentally controlled full-scale laboratory chamber (87 m3), and an indoor therapy pool building, the mitigation ability of air filters was assessed by comparing concentrations of total bacteria, culturable bacteria, and airborne endotoxin with and without the air filters operating under otherwise similar conditions. Controlled chamber tests with pure cultures of aerosolized Mycobacterium parafortuitum cells showed that the HUVAF unit tested provided an equivalent air-exchange rate of 11 hr(-1). Using this equivalent air-exchange rate as a design basis, three HUVAFs were installed in an indoor therapy pool building for bioaerosol mitigation, and their effectiveness was studied over a 2-year period. The HUVAFs reduced concentrations of culturable bacteria by 69 and 80% during monitoring periods executed in respective years. The HUVAFs reduced concentrations of total bacteria by 12 and 76% during the same monitoring period, respectively. Airborne endotoxin concentrations were not affected by the HUVAF operation.     

Indoor air quality differences between urban and rural preschools in Korea

Background, aims, and scope

Preschool indoor air quality (IAQ) is believed to be different from elementary school or higher school IAQ and preschool is the first place for social activity. Younger children are more susceptible than higher-grade children and spend more time indoors. The purpose of this study was to compare the indoor air quality by investigating the concentrations of airborne particulates and gaseous materials at preschools in urban and rural locations in Korea.

Methods

We investigated the concentrations of airborne particulates and gaseous materials in 71 classrooms at 17 Korean preschools. For comparison, outdoor air was sampled simultaneously with indoor air samples. Airborne concentrations of total suspended particulates, respirable particulates, lead, asbestos, total volatile organic compounds and components, formaldehyde, and CO₂ were measured with National Institute for Occupational Safety and Health and/or Environmental Protection Agency analytical methods.

Results

The concentration profiles of the investigated pollutants in indoor and urban settings were higher than those in outdoor and rural areas, respectively. The ratios of indoor/outdoor concentrations (I/O) of particulates and gaseous pollutants were characterized in urban and rural preschools. Total dust concentration was highest in urban indoor settings followed by urban outdoor, rural indoor, and rural outdoor locations with an I/O ratio of 1.37 in urban and 1.35 in rural areas. Although I/O ratios of lead were close to 1, lead concentrations were much higher in urban than in rural areas. The I/O ratio of total VOCs was 2.29 in urban and 2.52 in rural areas, with the highest level in urban indoor settings. The I/O ratio of formaldehyde concentrations was higher in rural than in urban areas because the outdoor rural level was much lower than the urban concentration. Since an I/O ratio higher than 1 implies the presence of indoor sources, we concluded that there are many indoor sources in preschools.

Conclusions

We confirmed that pollutants in indoor and urban settings were higher than those in outdoor and rural areas, respectively. Preschool children are expected to spend more time inside preschool facilities and therefore to be more exposed to pollutants. As far as we know, preschool IAQ is different from elementary school or higher school IAQ. Also, they are more vulnerable than higher-grade children. We found that the indoor and urban concentration profiles of the studied pollutants in preschools were higher than those in outdoor and rural areas. We believe that our findings may be useful for understanding the potential health effects of exposure and intervention studies in preschools.     

A method of assessing air toxics concentrations in urban areas using mobile platform measurements

The objective of this paper is to demonstrate an approach to characterize the spatial variability in ambient air concentrations using mobile platform measurements. This approach may be useful for air toxics assessments in Environmental Justice applications, epidemiological studies, and environmental health risk assessments. In this study, we developed and applied a method to characterize air toxics concentrations in urban areas using results of the recently conducted field study in Wilmington, DE. Mobile measurements were collected over a 4- x 4-km area of downtown Wilmington for three components: formaldehyde (representative of volatile organic compounds and also photochemically reactive pollutants), aerosol size distribution (representing fine particulate matter), and water-soluble hexavalent chromium (representative of toxic metals). These measurements were,used to construct spatial and temporal distributions of air toxics in the area that show a very strong temporal variability, both diurnally and seasonally. An analysis of spatial variability indicates that all pollutants varied significantly by location, which suggests potential impact of local sources. From the comparison with measurements at the central monitoring site, we conclude that formaldehyde and fine particulates show a positive correlation with temperature, which could also be the reason that photochemically generated formaldehyde and fine particulates over the study area correlate well with the fine particulate matter measured at the central site.     

Neural network modelling and prediction of hourly NOx and NO2 concentrations in urban air in London

Multilayer perceptron (MLP) neural networks were trained to model hourly NO_x and NO₂ pollutant concentrations in Central London from basic hourly meteorological data. Results have shown that the models perform well when compared to previous attempts to model the same pollutants using regression based models. This work also illustrates that MLP neural networks are capable of resolving complex patterns of source emissions without any explicit external guidance.     

The relationships between air pollutants, meteorological parameters and concentration of airborne fungal spores

Fungal spores are an important component of bioaerosol and also considered to act as indicator of the level of atmospheric bio-pollution. Therefore, better understanding of these phenomena demands a detailed survey of airborne particles.The objective of this study was to examine the dependence of two the most important allergenic taxa of airborne fungi - Alternaria and Cladosporium - on meteorological parameters and air pollutant concentrations during three consecutive years (2006-2008). This study is also an attempt to create artificial neural network (ANN) forecasting models useful in the prediction of aeroallergen abundance.There were statistically significant relationships between spore concentration and environmental parameters as well as pollutants, confirmed by the Spearman’s correlation rank analysis and high performance of the ANN models obtained. The concentrations of Cladosporium and Alternaria spores can be predicted with quite good accuracy from meteorological conditions and air pollution recorded three days earlier.