Showing papers by "Lidia Morawska published in 2008"

Ozone modifies associations between temperature and cardiovascular mortality: analysis of the NMMAPS data.

Abstract: Objectives: Both ambient ozone and temperature are associated with human health. However, few data are available on whether ozone modifies temperature effects. This study aims to explore whether ozone modified associations between maximum temperature and cardiovascular mortality in the USA. Methods: The authors obtained data from the US National Morbidity, Mortality, and Air Pollution Study (NMMAPS) website. They used two time-series Poisson regression models (a response surface model and a stratification model) to examine whether ozone modified associations between maximum temperature and cardiovascular mortality (CVM) in 95 large US communities during 1987–2000 in summer (June to September). Bayesian meta-analysis was used to pool estimates in each community. Results: The response surface model was used to examine the joint effects of temperature and ozone on CVM in summer. Results indicate that ozone positively modified the temperature-CVM associations across the different regions. The stratification model quantified the temperature-CVM associations across different levels of ozone. Results show that in general the higher the ozone concentration, the stronger the temperature-CVM associations across the communities. A 10uC increase in temperature on the same day was associated with an increase in CVM by 1.17% and 8.31% for the lowest and highest level of ozone concentrations in all communities, respectively. Conclusion: Ozone modified temperature effects in different regions in the USA. It is important to evaluate the modifying role of ozone when estimating temperaturerelated health impacts and to further investigate the reasons behind the regional variability and mechanism for the interaction between temperature and ozone.

Impact of ventilation scenario on air exchange rates and on indoor particle number concentrations in an air-conditioned classroom

Abstract: A two-week intensive measurement campaign of indoor and outdoor air pollution was carried out in September 2006, in a primary school to investigate indoor-outdoor correlations of particle number concentrations (PN), and the impact of air exchange rate (ACH) on the indoor PN concentration. The ACHs in the classroom for different conditions associated with window opening and the operational status of air conditioners (A/C) and fans were tested. As expected, the lowest ACH (0.12 h-1) was found when the windows were closed and A/C and fans were off. In contrast, the highest ACH (7.92 h-1) was observed when the windows were opened and A/C and fans were all on. The analysis of the PN I/O ratios at different ACHs in the absence of indoor sources indicates that the mean I/O ratio was 0.621 ± 0.007 (mean ± 95% confidence interval) when the windows were closed, and A/C and fans were off; 0.524 ± 0.023 when windows were closed, fans were off and A/C was on; and 0.502 ± 0.029 when windows were closed, A/C was off and fans were on. To further understand the relationship between indoor and outdoor PN concentrations, the impact of outdoor PN concentration on I/O ratios at different ACHs was investigated. It was found that the relationship between outdoor PN concentration and the I/O ratio at different ACHs followed a power trendline with an equation of I/O ratio = A*PNout-b (A and b are coefficients, PNout is outdoor PN concentration), suggesting that the penetration efficiency decreased with increasing outdoor PN concentration. It is the first time we found that when the outdoor PN concentration increased there was an associated increase in the concentration of nano-particles, which have been demonstrated to have higher deposition rates and lower penetration efficiencies. Based on the above equation, the study also showed a significant effect of ACH on indoor PN concentrations under stable outdoor PN concentrations. In general, the higher the ACH was, the lower the indoor PN concentration was.

Does temperature modify short-term effects of ozone on total mortality in 60 large eastern US communities? — An assessment using the NMMAPS data

Abstract: Many studies have indicated that ozone is associated with morbidity and mortality. A few studies have reported that the association is heterogeneous across seasons and geographic regions. However, little information is available on whether both temperature and geographic factors simultaneously modify the ozone effect. This study used a Poisson regression model to explore whether temperature modifies the effect of ozone on mortality in the 60 large eastern US communities during April to October, 1987–2000. Results show that temperature modified ozone-mortality associations and that such modification varied across geographic regions. In the northeast region, a 10-ppb increment in ozone was associated with an increase of 2.22% (95% posterior interval [PI]: 1.19%, 3.13%), 3.06% (95% PI: 2.21%, 3.76%) and 6.22% (95% PI: 4.77%, 7.56%) in mortality at low, moderate and high temperature level, respectively, while in the southeast region a 10-ppb increment in ozone was associated with an increase of 1.13% (95% PI:− 1.12%, 3.18%), 1.50% (95% PI: 0.22%, 2.81%) and 1.29% (95% PI:− 0.33%, 2.96%) in mortality, respectively. We concluded that temperature synergistically modified the ozone-mortality association in the northeast region, but such a pattern was not apparent in the southeast region. Thus, both temperature and geographic factors should be considered in the assessment of ozone effects.

Evaluation of Ultrafine Particle Emissions from Laser Printers Using Emission Test Chambers

Abstract: It has now been recognized that some hardcopy devices emit ultrafine particles (dp < 100 nm) during their operation. As a consequence, the time-dependent characterization of particle release from laser printers is of high interest in order to evaluate the exposure of office workers to such emissions. The emission profiles of different printers can be compared in test chambers using a standardized test protocol and measuring devices with high time resolution. The extraction of meaningful and comparable data from the obtained data set is a complex procedure due to the different emission behavior patterns of the printers. The calculation of the unit specific emission rate (SERu) is of limited use because the emission profiles during the printing process ranged between short-term bursts and constant particle release. Therefore, other parameters such as the particle loss-rate coefficient, β, which provides information about the testing conditions, and the area below the time vs concentration curve, F, which ch...

Distribution of respiratory droplets in enclosed environments under different air distribution methods

Abstract: The dispersion characteristics of respiratory droplets are important in controlling transmission of airborne diseases indoors. This study investigates the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets within the range of 1.0 − 10.0μm in an office room with three air distribution methods, specifically mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD). The diffusion, gravitational settling and deposition mechanism of particulate matter were accounted by using an Eulerian modeling approach with one-way coupling. The simulation results indicate that exhaled droplets up to 10μm in diameter from normal human respiration are uniformly distributed in MV. However, they become trapped in the breathing zone by thermal stratifications in DV and UFAD, resulting in a higher droplet concentration and an increased exposure risk to other room occupants. Sneezed/coughed droplets are more slowly diluted in DV/UFAD than in MV. Low air speed in the breathing zone in DV/UFAD can lead to prolonged human exposure to droplets in the breathing zone.

The effect of temperature and humidity on size segregated traffic exhaust particle emissions

Abstract: The formation and behaviour of exhaust emissions is affected by environmental, traffic and meteorological conditions. The understanding of the governing processes and dependency between particles and other relevant parameters, as well as the magnitude of the impacts, is still limited and mostly based on a few laboratory studies. The focus of this work is the effect of temperature (TEMP) and relative humidity (RH) and their interaction on traffic emission particles in the size range of 15-850 nm. The relationship was assessed using a large data set collected over a period of six months at two road sites in Brisbane. A sequence of statistical analyses were designed and applied in order to quantify the relationships, comprising of exploratory correlation analysis to identify pairwise linear associations, factor analysis to assess multivariate effects and nonparametric regression tree methods to more carefully explore interactions. The results show that total particle number concentration was dominated by traffic flow rate and wind speed and to a lesser degree by RH and TEMP. In general, an inverse relationship between temperature and concentration, and a direct relationship between RH and concentration was observed. While TEMP was a dominant parameter for particle concentrations in the size range 15-30 nm, its role diminished and RH emerged as a stronger influence as particle size increased. The observed increase for particle concentrations in the size range 50-150 nm could be associated with particle transfer from a smaller to larger size group due to coagulation and condensation induced growth, as well as an increase in primary (engine) emissions. The significant influence of RH on particles in the 150-880 nm size range could be related to particle growth, changes in hygroscopic properties of traffic emissions and particles originating from sources other than traffic. Decreased combustion efficiency may also contribute to higher emissions of particles in this size range.

Spatial variation in particle number size distributions in a large metropolitan area

Abstract: Air quality studies have indicated that particle number size distribution (NSD) is unevenly spread in urban air. To date, these studies have focussed on differences in concentration levels between sampling locations rather than differences in the underlying geometries of the distributions. As a result, the existing information on the spatial variation of the NSD in urban areas remains incomplete. To investigate this variation in a large metropolitan area in the southern hemisphere, NSD data collected at nine different locations during different campaigns of varying duration were compared using statistical methods. The spectra were analysed in terms of their modal structures (the graphical representation of the number size distribution function), cumulative distribution and number median diameter (NMD). The study found that with the exception of one site all distributions were bimodal or suggestive of bimodality. In general, peak concentrations were below 30 nm and NMDs below 50 nm, except at a site dominated by diesel trucks, where it shifted to around 50 and 60 nm respectively. Ultrafine particles (UFPs (<100 nm)) contributed to 82–90% of the particle number, nanoparticles (<50 nm) to around 60–70%, except at the diesel traffic site, where their contribution dropped to 50%. Statistical analyses found that the modal structures heterogeneously distributed throughout Brisbane whereas it was not always the case for the NMD. The discussion led to the following site classification: (1) urban sites dominated by petrol traffic, (2) urban sites affected by the proximity to the road and (3) an isolated site dominated by diesel traffic. Comparisons of weekday and weekend data indicated that, the distributions were not statistically different. The only exception occurred at one site, where there is a significant drop in the number of diesel buses on the weekend. The differences in sampling period between sites did not affect the results. The statistics instead suggested variations in traffic composition. However, the relative contribution of petrol vehicle emissions at each site could not be assessed due to the limited traffic information available.

Spatial variation in particle number size distributions in a large metropolitan area

Abstract: Air quality studies have indicated that particle number size distribution (NSD) is unevenly spread in urban air. To date, these studies have focussed on differences in concentration levels between sampling locations rather than differences in the underlying geometries of the distributions. As a result, the existing information on the spatial variation of the NSD in urban areas remains incomplete. To investigate this variation in a large metropolitan area in the southern hemisphere, NSD data collected at nine different locations during different campaigns of varying duration were compared using statistical methods. The spectra were analysed in terms of their modal structures (the graphical representation of the number size distribution function), cumulative distribution and number median diameter (NMD). The study found that with the exception of one site all distributions were bimodal or suggestive of bimodality. In general, peak concentrations were below 30 nm and NMDs below 50 nm, except at a site dominated by diesel trucks, where it shifted to around 50 and 60 nm respectively. Ultrafine particles (UFPs (< 100 nm)) contributed to 82-90% of the particle number, nanoparticles (< 50 nm) to around 60-70%, except at the diesel traffic site, where their contribution dropped to 50%. Statistical analyses found that the modal structures heterogeneously distributed throughout Brisbane whereas it was not always the case for the NMD. The discussion led to the following site classification: (1) urban sites dominated by petrol traffic, (2) urban sites affected by the proximity to the road and (3) an isolated site dominated by diesel traffic. Comparisons of weekday and weekend data indicated that, the distributions were not statistically different. The only exception occurred at one site, where there is a significant drop in the number of diesel buses on the weekend. The differences in sampling period between sites did not affect the results. The statistics instead suggested variations in traffic composition. However, the relative contribution of petrol vehicle emissions at each site could not be assessed due to the limited traffic information available.

A comparative investigation of ultrafine particle number and mass emissions from a fleet of on-road diesel and CNG buses

Abstract: Particle number, particle mass, and CO2 concentrations were measured on the curb of a busy urban busway used entirely by a mix of diesel and CNG operated buses. With the passage of each bus, the ratio of particle number concentration and particle mass concentration to CO2 concentration in the diluted exhaust plume were used as measures of the particle number and mass emission factors, respectively. With all buses accelerating pastthe monitoring point, the results showed that the median particle mass emission from CNG buses was less than 9% of that from diesel buses. However, the median particle number emission from CNG buses was 6 times higher than the diesel buses, and the particles from the CNG buses were mainly in the nanoparticle size range. Using a thermodenuder to remove the volatile material from the sampled emissions showed that the majority of particles from the CNG buses, but not from the diesel buses, were volatile. Approximately, 82% of the particles from the CNG buses and 38% from the diesel buses were removed by heating the emissions to 300 degrees C.

A plume capture technique for the remote characterization of aircraft engine emissions.

Abstract: A technique for capturing and analyzing plumes from unmodified aircraft or other combustion sources under real world conditions is described and applied to the task of characterizing plumes from commercial aircraft during the taxiing phase of the Landing/Take-Off (LTO) cycle. The method utilizes a Plume Capture and Analysis System (PCAS) mounted in a four-wheel drive vehicle which is positioned in the airfield 60 to 180 meters downwind of aircraft operations. The approach offers low test turnaround times with the ability to complete careful measurements of particle and gaseous emission factors and sequentially scanned particle size distributions without distortion due to plume concentration fluctuations. These measurements can be performed for individual aircraft movements at five minute intervals. A Plume Capture Device (PCD) collected samples of the naturally diluted plume in a 200 L conductive membrane conforming to a defined shape. Samples from over 60 aircraft movements were collected and analyzed in-situ for particulate and gaseous concentrations and for particle size distribution using a Scanning Particle Mobility Sizer (SMPS). Emission factors are derived for particle number, NOx and PM2.5 for a widely used commercial aircraft type; Boeing 737 airframes with predominantly CFM56 class engines, during taxiing. The practical advantages of the PCAS, include the capacity to perform well targeted and controlled emission factor and size distribution measurements using instrumentation with varying response times within an airport facility, in close proximity to aircraft during their normal operations.

A Plume Capture Technique for the Remote Characterization of Aircraft Engine Emissions

Abstract: A technique for capturing and analyzing plumes from unmodified aircraft or other combustion sources under real world conditions is described and applied to the task of characterizing plumes from commercial aircraft during the taxiing phase of the Landing/Take-Off (LTO) cycle. The method utilizes a Plume Capture and Analysis System (PCAS) mounted in a four-wheel drive vehicle which is positioned in the airfield 60 to 180 meters downwind of aircraft operations. The approach offers low test turnaround times with the ability to complete careful measurements of particle and gaseous emission factors and sequentially scanned particle size distributions without distortion due to plume concentration fluctuations. These measurements can be performed for individual aircraft movements at five minute intervals. A Plume Capture Device (PCD) collected samples of the naturally diluted plume in a 200 L conductive membrane conforming to a defined shape. Samples from over 60 aircraft movements were collected and analyzed in-situ for particulate and gaseous concentrations and for particle size distribution using a Scanning Particle Mobility Sizer (SMPS). Emission factors are derived for particle number, NOx and PM2.5 for a widely used commercial aircraft type; Boeing 737 airframes with predominantly CFM56 class engines, during taxiing. The practical advantages of the PCAS, include the capacity to perform well targeted and controlled emission factor and size distribution measurements using instrumentation with varying response times within an airport facility, in close proximity to aircraft during their normal operations.

Droplets expelled during human expiratory activities and their origin

Abstract: This paper presents the findings of the most comprehensive program of study to date aimed at quantifying the number, size distribution and evaporation of droplets produced during virtually any expiratory activity. This international research program included teams of investigators from a number of universities, with each group contributing to essential aspects of the research. This research revealed many previously unknown aspects of expiratory aerosol dynamics and characteristics. This paper will focus on the findings that the time taken for expiratory droplets to achieve short term equilibrium is comparable to that for pure water droplets and that the droplet size distributions have distinct features reflecting specific production mechanisms whose intensity varies with the nature of the activity.

Size distribution and new particle formation in subtropical eastern Australia

Abstract: Environmental context. Atmospheric submicrometre particles have a significant impact on human health, visibility impairment, acid deposition and global climate. This study aims to understand the size distribution of submicrometre particles and new particle formation in eastern Australia and the results indicate that photochemical reactions of airborne pollutants are the main mechanism of new particle formation. The findings will contribute to a better understanding of the effects of aerosols on climate and the reduction of submicrometre particles in the atmosphere. Abstract. An intensive measurement campaign of particle concentrations, nitrogen oxides and meteorological parameters was conducted at a rural site in subtropical eastern Australia during September 2006. The aim of this work was to develop an understanding of the formation and growth processes of atmospheric aerosols, and the size distributions under various meteorological conditions. In order to achieve this, the origins of air arriving at the site were explored using back trajectories cluster analysis and the diurnal patterns of particle number concentration and size distribution for the classified air masses were investigated. The study showed that the photochemical formation of nucleation mode particles and their consequent growth was often observed. Furthermore, the nucleation mode usually dominated the size distribution and concentration of the photochemical event in the first 3–4 h with a geometric mean diameter of 26.9 nm and a geometric standard deviation of 1.28. The average particle growth rate was estimated to be 1.6 nm h–1, which is lower than that observed at urban sites, but comparable to the values reported in clean environments. The potential precursors of the photochemical events are also discussed.

Development of a methodology for the quantification of particle number and gaseous concentrations in a bidirectional bus tunnel and the derivation of emission factors

Abstract: Particle number, NOx and CO concentrations were measured simultaneously at the air entry portal and at the mid-point of a 511m bi-directional road tunnel, used entirely by urban public transport buses. The aim of this study was to provide information on concentrations of these pollutants inside a unique bus tunnel, and to develop a viable methodology for determining emission factors for on-road vehicles. Measurements were made continuously over a period of five days that included a complete weekend. Traffic flow rate and air flow rate were also monitored. The mean particle number concentration at mid-tunnel was 4.1 x 104 cm-3, which was over four times higher than the urban background concentration. The mean concentrations of NOx and CO at mid-tunnel were 464 ppb and 802 ppb, respectively. All these values were between 2 and 4 times higher than at the air entry portal. Median concentrations during selected time segments coinciding with the morning and evening rush hours, mid-day during weekdays and full day during the weekends were determined and the corresponding bus emission factors of each of the three parameters was calculated. Mean emission factors found for particle number, NOx and CO were 7.1 x 1014 particles km-1, 8.1 g km-1 and 15.9 g km-1, respectively. These values compared well with previous studies, showing that the methodology adopted was sound and viable.

Particle emission from laser printers

Abstract: Recent studies have shown that the operation of laser printers can result in the emission of high concentrations of ultrafine particles. However, fundamental gaps in knowledge still remain, for example, it is not clear what makes a printer a high emitter or why some models alternate between being low and high emitters. In order to provide insight into the formation mechanisms of these particles, comprehensive investigations into particle emissions from one high and one low emitting printer were undertaken. Each printer was operated using its own toner, and printed on two types of paper. Emissions from the printers were studied in a flow tunnel and a box chamber, while emissions from the fuser rollers, two types of paper and toner were investigated in a furnace. This paper provides examples of preliminary results from the study, taken from the extensive body of data which has been collected and analysed so far.

A Comparative Investigation of Ultrafine Particle Number and Mass Emissions from a Fleet of On-road Diesel and CNG Buses

Abstract: Particle number, particle mass and CO2 concentrations were measured on the kerb of a busy urban busway used entirely by a mix of diesel and CNG operated buses. With the passage of each bus, the ratio of particle number concentration and particle mass concentration to CO2 concentration in the diluted exhaust plume were used as measures of the particle number and mass emission factors, respectively. With all buses accelerating past the monitoring point, the results showed that the median particle mass emission from CNG buses was less than 9% of that from diesel buses. However, the median particle number emission from CNG buses was six times higher than the diesel buses and the particles from the CNG buses were mainly in the nanoparticle size range. Using a thermodenuder to remove the volatile material from the sampled emissions showed that the majority of particles from the CNG buses, but not from the diesel buses, were volatile. Approximately, 82% of the particles from the CNG buses and 38% from the diesel buses were removed by heating the emissions to 300°C.

Characterization of the atmospheric electrical environment near a corona ion-emitting source

Abstract: Presence of high concentrations of corona ions in any air environment cause changes in the earth’s natural dc e-field; while their interaction with airborne aerosols produce charged particles. The charged particles and ions are dispersed by wind, and depending on the prevailing meteorology, their presence can be observed several hundreds of meters from the ion source. This paper presents a study characterizing the electrical environment of a strong substantially-constant source of corona ions (a high voltage electricity substation). Results of the study showed that corona ion and particle charge concentrations as well as their associated effect on the vertical dc e-field perturbations decreased with distance from the emitting source. Mean particle charge concentration in the air environment of the ion emitting source (-1750 ± 745 ions cm-3) was three times higher than that of an urban outdoor air and seventeen times that of a mechanically ventilated room. Statistical investigation of possible associations between parameters showed strong associations (R2 = 74%, P<0.05) between particle charge and ion concentration; and 54% correlation between particle charge and magnitude of the vertical dc e-field (mean value of -285 ± 51 V m-1). Although a source of ambient electrical charge, the electricity substation was not a significant generator of aerosol particles within the size range (0.02 to 1 μm) examined in this study.

Droplets Expelled during Human Expiratory Activities and their Origins

Abstract: This paper presents the findings of the most comprehensive program of study to date aimed at quantifying the number, size distribution and evaporation of droplets produced during virtually any expiratory activity. This international research program included teams of investigators from a number of universities, with each group contributing to essential aspects of the research. This research revealed many previously unknown aspects of expiratory aerosol dynamics and characteristics. This paper will focus on the findings that the time taken for expiratory droplets to achieve short term equilibrium is comparable to that for pure water droplets and that the droplet size distributions have distinct features reflecting specific production mechanisms whose intensity varies with the nature of the activity.

Modality in ambient particle size distributions and its potential as a basis for developing air quality regulation

Abstract: Current ambient air quality standards are mass-based and restricted to PM2.5 and PM10 fractions. The major contribution to both PM2.5 and PM10 fractions is from particles belonging to the coarse mode and generated by mechanical processes. These standards are thus unable to effectively control particle concentrations from combustion sources, such as motor vehicles and power plants, which tend to emit very small particles that are almost entirely respirable and in the submicron range, and dominate the nucleation and accumulation modes, which contribute much less to particle mass concentration. The aim of this work was to examine whether PM1 and PM10 would be a more effective combination of mass standards than PM2.5 (dominant in the nucleation and accumulation modes) and PM10 (dominant in the coarse mode) in controlling combustion related ambient particles, as well as those originating from mechanical processes. Firstly, a large body of data on particle size distributions in a range of environments in South East Queensland, Australia was analysed, with an aim of identifying the relation between modality in the distributions and sources of particles belonging to different modes. The analyses included a matrix of the following elements: particle volume and number distributions, type of environment and locations of the modes in the range of PM1, PM2.5 and PM10 fractions. Secondly, with the same aim, 600 published modal location values relating to number, surface area, volume and mass size distributions for a range of environments worldwide, were analysed. The analysis identified a clear and distinct separation between the location of the modes for a substantial number of environments worldwide and particle metrics, which suggests that modality in particle size distributions may be a parameter that has potential to be used in the development of PM1 air quality guidelines and standards. Based on these analyses, implications for choosing different mass standards for airborne particulate matter are discussed in the paper.