M. Jamriska - Academia.edu (original) (raw)

Papers by M. Jamriska

Research paper thumbnail of Statistical characterisation of bio-aerosol background in an urban environment

Atmospheric Environment, Feb 23, 2012

In this paper we statistically characterise the bio-aerosol background in an urban environment. T... more In this paper we statistically characterise the bio-aerosol background in an urban environment. To do this we measure concentration levels of naturally occurring microbiological material in the atmosphere over a two month period. Naturally occurring bioaerosols can be considered as noise, as they mask the presence of signals coming from biological material of interest (such as an intentionally released biological agent). Analysis of this 'biobackground' was undertaken in the 1-10µm size range and a 3-9% contribution was found to be biological in origin -values which are in good agreement with other studies reported in the literature. A model based on the physics of turbulent mixing and dispersion was developed and validated against this analysis. The Gamma distribution (the basis of our model) is shown to comply with the scaling laws of the concentration moments of our data, which enables us to universally characterise both biological and non-biological material in the atmosphere. An application of this model is proposed to build a framework for the development of novel algorithms for bio-aerosol detection and rapid characterisation.

Research paper thumbnail of Release Limitation

CS aerosol (o-chlorobenzylidene malonitrile) is a low to moderate toxicity irritant used by Austr... more CS aerosol (o-chlorobenzylidene malonitrile) is a low to moderate toxicity irritant used by Australian Defence Force for respiratory protection training. It is classified as a hazardous substance with an occupational exposure limit of 0.39 mg/m3 (STEL-C). Currently the ADF has no means of measuring the concentration of CS aerosol used within the Mask Test Facilities (MTF) during CBRN training. Driven by the health concern associated with CS exposure to personnel in MTF, this study aimed to: (i) characterise the physico-chemical properties of CS aerosol; (ii) validate the use of a commercial off-the-shelf equipment to monitor CS aerosol concentrations, and (iii) quantify CS levels in MTF. The CS aerosol was identified as a poly-disperse, uni-modal aerosol with a dominant peak at 0.26 micrometers. The COTS optical photometer DustTrak, (TSI Inc Model 8520) was validated to accurately measure CS aerosol concentration. As anticipated, the CS levels in the MTF exceeded the concentrations ...

Research paper thumbnail of Quantifying the reduction of airborne infectious viral load using a ventilated patient hood

Journal of Hospital Infection

Research paper thumbnail of Dispersion of particles by a strong explosion

Physical Review E, 2015

The dynamics of particle transport under the influence of localised high energy anomalies (explos... more The dynamics of particle transport under the influence of localised high energy anomalies (explosions) is a complicated phenomena dependent on many physical parameters of both the particle and the medium it resides in. Here we present a conceptual model that establishes simple scaling laws for particle dispersion in relation to the energy released in a blast, properties of the medium, physical properties of particles and their initial position away from a blast epicenter. These dependencies are validated against numerical simulations and we discuss predictions of the model which can be validated experimentally. Other applications and extensions to the framework are also considered.

Research paper thumbnail of Scaling laws of passive tracer dispersion in the turbulent surface layer

Physical Review E, 2010

Experimental results for passive tracer dispersion in the turbulent surface layer under stable co... more Experimental results for passive tracer dispersion in the turbulent surface layer under stable conditions are presented. In this case, the dispersion of tracer particles is determined by the interplay of three mechanisms: relative dispersion (celebrated Richardson's mechanism), shear dispersion (particle separation due to variation of the mean velocity field) and specific surface-layer dispersion (induced by the gradient of the energy dissipation rate in the turbulent surface layer). The latter mechanism results in the rather slow (ballistic) law for the mean squared particle separation. Based on a simplified Langevin equation for particle separation we found that the ballistic regime always dominates at large times. This conclusion is supported by our extensive atmospheric observations. Exit-time statistics are derived from the experimental dataset and show a reasonable match with the simple dimensional asymptotes for different mechanisms of tracer dispersion, as well as predictions of the multifractal model and experimental data from other sources.

Research paper thumbnail of Performance assessment of electrostatic filters with a focus on submicrometer particles

Journal of Aerosol Science, 1998

Research paper thumbnail of Relation between Indoor and Outdoor Exposure to Fine Particles near a Busy Arterial Road

Indoor Air, 1999

Relation between indoor and outdoor exposure to fine particles near a busy arterial road.. Indoor... more Relation between indoor and outdoor exposure to fine particles near a busy arterial road.. Indoor Air 9(2):pp. 75-84.

Research paper thumbnail of Particulate Matter in the Hospital Environment

Indoor Air, 1998

Investigations of particle concentration levels and size distribution were conducted in the compl... more Investigations of particle concentration levels and size distribution were conducted in the complex hospital system of the Royal Children's and the Royal Brisbane Hospitals. The aim of the measurements was to provide an indication of particulate sources in the hospital environment and relate particle characteristics to the operating parameters of the hospitals. The measurements were performed using the most advanced instrumentation for size classification in the submicrometer and supermicrometer levels. The conclusions from the investigation were (i) that indoor concentration levels of particle numbers are closely related to outdoor concentration levels, indicating that outdoor particulates were 2 the main contributor to the indoor particulates in the hospitals under investigations and (ii) that the performance of filtration/ventilation systems is the most critical parameter in reducing general particulate concentration levels in those hospital units where medical procedures can result in generation of potentially hazardous organic aerosols.

Research paper thumbnail of Statistical characterisation of bio-aerosol background in an urban environment

Atmospheric Environment, 2012

In this paper we statistically characterise the bio-aerosol background in an urban environment. T... more In this paper we statistically characterise the bio-aerosol background in an urban environment. To do this we measure concentration levels of naturally occurring microbiological material in the atmosphere over a two month period. Naturally occurring bioaerosols can be considered as noise, as they mask the presence of signals coming from biological material of interest (such as an intentionally released biological agent). Analysis of this 'biobackground' was undertaken in the 1-10µm size range and a 3-9% contribution was found to be biological in origin-values which are in good agreement with other studies reported in the literature. A model based on the physics of turbulent mixing and dispersion was developed and validated against this analysis. The Gamma distribution (the basis of our model) is shown to comply with the scaling laws of the concentration moments of our data, which enables us to universally characterise both biological and non-biological material in the atmosphere. An application of this model is proposed to build a framework for the development of novel algorithms for bio-aerosol detection and rapid characterisation.

Research paper thumbnail of Differences in airborne particle and gaseous concentrations in urban air between weekdays and weekends

Atmospheric Environment, 2002

Thomas, Stephen B. (2002) Differences in airborne particle and gaseous concentrations in urban ai... more Thomas, Stephen B. (2002) Differences in airborne particle and gaseous concentrations in urban air between weekdays and weekends. Atmospheric Environment 36(27):pp. 4375-4383.

Research paper thumbnail of Evaluation of electrostatic precipitator performance for submicron particle size range

Research paper thumbnail of Size distribution of particles emitted from grass fires in the Northern Territory, Australia

Atmospheric Environment, 2007

This study investigated particle size distributions from the burning of several grass species, un... more This study investigated particle size distributions from the burning of several grass species, under controlled laboratory conditions, and also in the field, conducted during the dry season in the Northern Territory, Australia. The laboratory study simulated conditions such as burning phases and burning rate, and particle diameter differed depending on the burning conditions. Under fast burning conditions, smaller particles were produced with a diameter in the range of 30-60nm, whilst larger particles, with a diameter between 60-210nm, were produced during slow burning. The airborne field measurements of biomass particles found that under the boundary layer most of the early dry season (EDS) particles came from fresh smokes with a CMD of 83 ± 13nm, and most of the late dry season (LDS) particles came from aged smokes with a CMD of 127 ± 6nm. Vertical profiles of CMD showed that smaller particles were found higher within the atmosphere. These measurements provide insight into the scientific understanding of the properties of biomass burning particles in the Northern Territory, Australia.

Research paper thumbnail of Quantification of aerosol losses in mechanical exhaust and balanced air flow ventilation systems

Highly-efficient balanced air flow ventilation systems increased from 5 to 50% in market share wi... more Highly-efficient balanced air flow ventilation systems increased from 5 to 50% in market share within six years for new residential buildings in The Netherlands. This success is based on the contribution of the system to energy performance in combination with cost effectiveness. Occupants’ complaints indicate that installation and maintenance quality need further improvement. One of the complaints relates to particle deposition. For better understanding of the impact of ducted air on particle distribution, experiments were performed with a full scale system in a test chamber. The presented results focus on aerosols deposition in the heat recovery unit and in the ducts, including components like dampers, sound attenuators, tees and bends. The deposition was measured under different ventilation scenarios, for the particles of size range 0.7-15 micrometers. The results show high deposition rate: 10-40% for total number concentration and with over 80% deposition of the larger particles....

Research paper thumbnail of Sources of ultrafine particles and chemical species along a traffic corridor: comparison of the results from two receptor models

Environmental Chemistry, 2013

Environmental context Identifying the sources responsible for air pollution is crucial for reduci... more Environmental context Identifying the sources responsible for air pollution is crucial for reducing the effect of the pollutants on human health. The sources of the pollutants were found here by applying two mathematical models to data consisting of particle size distribution and chemical composition data. The identified sources could be used as the basis for controlling or reducing emissions of air pollution into the atmosphere. Particulate matter is common in our environment and has been linked to human health problems particularly in the ultrafine size range. In this investigation, the sources of particles measured at two sites in Brisbane, Australia, were identified by analysing particle number size distribution data, chemical species concentrations and meteorological data with two source apportionment models. The source apportionment results obtained by positive matrix factorisation (PMF) and principal component analysis–absolute principal component scores (PCA–APCS) were compa...

Research paper thumbnail of Indoor air '99 - ventilation and filtration review

A general summary of the indoor Air '99 Conference held in Edinburgh in August 1999, was pres... more A general summary of the indoor Air '99 Conference held in Edinburgh in August 1999, was presented in the previous issue of Clean Air. Conferences in this series take place every three years and are the most important events in terms of gathering a large number of experts involved in various areas of lAQ. Thus, a summary of the material presented at the conference can serve as an oven/iew of the trends occurring and the directions for progress in this bro ad field internationally.

Research paper thumbnail of Investigation of the Filtration Efficiency of HEPA and ULPA Filters in Submicron Particle Size Range

High efficiency particulate (HEPA) and ultra low penetration air filters (ULPA) have been used as... more High efficiency particulate (HEPA) and ultra low penetration air filters (ULPA) have been used as filtration devices for more than fifty years. Their high efficiency makes them suitable for application in areas where clean room conditions or contamination control is required. This paper presents the results of a performance evaluation of HEPA and ULPA filters used at the Australian Animal Health Laboratory, Geelong, Victoria. A detailed description of the experimental system, test procedure, and measuring techniques is provided. HEPA and ULPA filter efficiencies were measured for both types of filters in single and tandem configurations, and for different airflow conditions. Particle counting technique and sodium flame method were applied, and the sensitivity of both techniques compared. The performance of a damaged HEPA filter was also investigated. The integrated efficiency of a HEPA filter, challenged with dry polydisperse NaCl aerosols of count median diameter 60 nm, at a flow r...

Research paper thumbnail of Vehicle emissions in Australia: From monitoring to modelling

Research paper thumbnail of Aerosol Size Distribution and Concentration in Various Units of a Children’s Hospital

Ventilation and Indoor Air Quality in Hospitals, 1996

Research paper thumbnail of Dispersion of particles by a strong explosion

The dynamics of particle transport under the influence of localized high energy anomalies (explos... more The dynamics of particle transport under the influence of localized high energy anomalies (explosions) is a complicated phenomenon dependent on many physical parameters of both the particle and the medium it resides in. Here we present a conceptual model that establishes simple scaling laws for particle dispersion in relation to the energy released in a blast, properties of the medium, physical properties of particles, and their initial position away from a blast epicenter. These dependencies are validated against numerical simulations and we discuss predictions of the model which can be validated experimentally. Other applications and extensions to the framework are also considered.

Research paper thumbnail of A comparative study of airborne particulate pollution at two bus stations of different site geography

Airborne particulate pollutant is considered to be one of the major harmful emissions produced by... more Airborne particulate pollutant is considered to be one of the major harmful emissions produced by vehicle engines as it has been directly linked to serious health problems. Passengers spend long times at bus stations and may be exposed to high concentrations of pollution. Particle pollution at two bus stations in Brisbane, Australia were monitored. The two bus stations consisted of markedly different site geography and surroundings with one situated in a street canyon and the other elevated above ground level. The same flow of traffic operated through both stations. Real time measurements of ultrafine particle concentration, size distribution and meteorological conditions were carried out on the platform continuously over several days. The results showed that the particle number concentrations were significantly different at the two stations, suggesting that the layout of site geometry and surroundings was a dominant determining factor through the injection of fresh air into the station platforms and the rates of dilution.

Research paper thumbnail of Statistical characterisation of bio-aerosol background in an urban environment

Atmospheric Environment, Feb 23, 2012

In this paper we statistically characterise the bio-aerosol background in an urban environment. T... more In this paper we statistically characterise the bio-aerosol background in an urban environment. To do this we measure concentration levels of naturally occurring microbiological material in the atmosphere over a two month period. Naturally occurring bioaerosols can be considered as noise, as they mask the presence of signals coming from biological material of interest (such as an intentionally released biological agent). Analysis of this 'biobackground' was undertaken in the 1-10µm size range and a 3-9% contribution was found to be biological in origin -values which are in good agreement with other studies reported in the literature. A model based on the physics of turbulent mixing and dispersion was developed and validated against this analysis. The Gamma distribution (the basis of our model) is shown to comply with the scaling laws of the concentration moments of our data, which enables us to universally characterise both biological and non-biological material in the atmosphere. An application of this model is proposed to build a framework for the development of novel algorithms for bio-aerosol detection and rapid characterisation.

Research paper thumbnail of Release Limitation

CS aerosol (o-chlorobenzylidene malonitrile) is a low to moderate toxicity irritant used by Austr... more CS aerosol (o-chlorobenzylidene malonitrile) is a low to moderate toxicity irritant used by Australian Defence Force for respiratory protection training. It is classified as a hazardous substance with an occupational exposure limit of 0.39 mg/m3 (STEL-C). Currently the ADF has no means of measuring the concentration of CS aerosol used within the Mask Test Facilities (MTF) during CBRN training. Driven by the health concern associated with CS exposure to personnel in MTF, this study aimed to: (i) characterise the physico-chemical properties of CS aerosol; (ii) validate the use of a commercial off-the-shelf equipment to monitor CS aerosol concentrations, and (iii) quantify CS levels in MTF. The CS aerosol was identified as a poly-disperse, uni-modal aerosol with a dominant peak at 0.26 micrometers. The COTS optical photometer DustTrak, (TSI Inc Model 8520) was validated to accurately measure CS aerosol concentration. As anticipated, the CS levels in the MTF exceeded the concentrations ...

Research paper thumbnail of Quantifying the reduction of airborne infectious viral load using a ventilated patient hood

Journal of Hospital Infection

Research paper thumbnail of Dispersion of particles by a strong explosion

Physical Review E, 2015

The dynamics of particle transport under the influence of localised high energy anomalies (explos... more The dynamics of particle transport under the influence of localised high energy anomalies (explosions) is a complicated phenomena dependent on many physical parameters of both the particle and the medium it resides in. Here we present a conceptual model that establishes simple scaling laws for particle dispersion in relation to the energy released in a blast, properties of the medium, physical properties of particles and their initial position away from a blast epicenter. These dependencies are validated against numerical simulations and we discuss predictions of the model which can be validated experimentally. Other applications and extensions to the framework are also considered.

Research paper thumbnail of Scaling laws of passive tracer dispersion in the turbulent surface layer

Physical Review E, 2010

Experimental results for passive tracer dispersion in the turbulent surface layer under stable co... more Experimental results for passive tracer dispersion in the turbulent surface layer under stable conditions are presented. In this case, the dispersion of tracer particles is determined by the interplay of three mechanisms: relative dispersion (celebrated Richardson's mechanism), shear dispersion (particle separation due to variation of the mean velocity field) and specific surface-layer dispersion (induced by the gradient of the energy dissipation rate in the turbulent surface layer). The latter mechanism results in the rather slow (ballistic) law for the mean squared particle separation. Based on a simplified Langevin equation for particle separation we found that the ballistic regime always dominates at large times. This conclusion is supported by our extensive atmospheric observations. Exit-time statistics are derived from the experimental dataset and show a reasonable match with the simple dimensional asymptotes for different mechanisms of tracer dispersion, as well as predictions of the multifractal model and experimental data from other sources.

Research paper thumbnail of Performance assessment of electrostatic filters with a focus on submicrometer particles

Journal of Aerosol Science, 1998

Research paper thumbnail of Relation between Indoor and Outdoor Exposure to Fine Particles near a Busy Arterial Road

Indoor Air, 1999

Relation between indoor and outdoor exposure to fine particles near a busy arterial road.. Indoor... more Relation between indoor and outdoor exposure to fine particles near a busy arterial road.. Indoor Air 9(2):pp. 75-84.

Research paper thumbnail of Particulate Matter in the Hospital Environment

Indoor Air, 1998

Investigations of particle concentration levels and size distribution were conducted in the compl... more Investigations of particle concentration levels and size distribution were conducted in the complex hospital system of the Royal Children's and the Royal Brisbane Hospitals. The aim of the measurements was to provide an indication of particulate sources in the hospital environment and relate particle characteristics to the operating parameters of the hospitals. The measurements were performed using the most advanced instrumentation for size classification in the submicrometer and supermicrometer levels. The conclusions from the investigation were (i) that indoor concentration levels of particle numbers are closely related to outdoor concentration levels, indicating that outdoor particulates were 2 the main contributor to the indoor particulates in the hospitals under investigations and (ii) that the performance of filtration/ventilation systems is the most critical parameter in reducing general particulate concentration levels in those hospital units where medical procedures can result in generation of potentially hazardous organic aerosols.

Research paper thumbnail of Statistical characterisation of bio-aerosol background in an urban environment

Atmospheric Environment, 2012

In this paper we statistically characterise the bio-aerosol background in an urban environment. T... more In this paper we statistically characterise the bio-aerosol background in an urban environment. To do this we measure concentration levels of naturally occurring microbiological material in the atmosphere over a two month period. Naturally occurring bioaerosols can be considered as noise, as they mask the presence of signals coming from biological material of interest (such as an intentionally released biological agent). Analysis of this 'biobackground' was undertaken in the 1-10µm size range and a 3-9% contribution was found to be biological in origin-values which are in good agreement with other studies reported in the literature. A model based on the physics of turbulent mixing and dispersion was developed and validated against this analysis. The Gamma distribution (the basis of our model) is shown to comply with the scaling laws of the concentration moments of our data, which enables us to universally characterise both biological and non-biological material in the atmosphere. An application of this model is proposed to build a framework for the development of novel algorithms for bio-aerosol detection and rapid characterisation.

Research paper thumbnail of Differences in airborne particle and gaseous concentrations in urban air between weekdays and weekends

Atmospheric Environment, 2002

Thomas, Stephen B. (2002) Differences in airborne particle and gaseous concentrations in urban ai... more Thomas, Stephen B. (2002) Differences in airborne particle and gaseous concentrations in urban air between weekdays and weekends. Atmospheric Environment 36(27):pp. 4375-4383.

Research paper thumbnail of Evaluation of electrostatic precipitator performance for submicron particle size range

Research paper thumbnail of Size distribution of particles emitted from grass fires in the Northern Territory, Australia

Atmospheric Environment, 2007

This study investigated particle size distributions from the burning of several grass species, un... more This study investigated particle size distributions from the burning of several grass species, under controlled laboratory conditions, and also in the field, conducted during the dry season in the Northern Territory, Australia. The laboratory study simulated conditions such as burning phases and burning rate, and particle diameter differed depending on the burning conditions. Under fast burning conditions, smaller particles were produced with a diameter in the range of 30-60nm, whilst larger particles, with a diameter between 60-210nm, were produced during slow burning. The airborne field measurements of biomass particles found that under the boundary layer most of the early dry season (EDS) particles came from fresh smokes with a CMD of 83 ± 13nm, and most of the late dry season (LDS) particles came from aged smokes with a CMD of 127 ± 6nm. Vertical profiles of CMD showed that smaller particles were found higher within the atmosphere. These measurements provide insight into the scientific understanding of the properties of biomass burning particles in the Northern Territory, Australia.

Research paper thumbnail of Quantification of aerosol losses in mechanical exhaust and balanced air flow ventilation systems

Highly-efficient balanced air flow ventilation systems increased from 5 to 50% in market share wi... more Highly-efficient balanced air flow ventilation systems increased from 5 to 50% in market share within six years for new residential buildings in The Netherlands. This success is based on the contribution of the system to energy performance in combination with cost effectiveness. Occupants’ complaints indicate that installation and maintenance quality need further improvement. One of the complaints relates to particle deposition. For better understanding of the impact of ducted air on particle distribution, experiments were performed with a full scale system in a test chamber. The presented results focus on aerosols deposition in the heat recovery unit and in the ducts, including components like dampers, sound attenuators, tees and bends. The deposition was measured under different ventilation scenarios, for the particles of size range 0.7-15 micrometers. The results show high deposition rate: 10-40% for total number concentration and with over 80% deposition of the larger particles....

Research paper thumbnail of Sources of ultrafine particles and chemical species along a traffic corridor: comparison of the results from two receptor models

Environmental Chemistry, 2013

Environmental context Identifying the sources responsible for air pollution is crucial for reduci... more Environmental context Identifying the sources responsible for air pollution is crucial for reducing the effect of the pollutants on human health. The sources of the pollutants were found here by applying two mathematical models to data consisting of particle size distribution and chemical composition data. The identified sources could be used as the basis for controlling or reducing emissions of air pollution into the atmosphere. Particulate matter is common in our environment and has been linked to human health problems particularly in the ultrafine size range. In this investigation, the sources of particles measured at two sites in Brisbane, Australia, were identified by analysing particle number size distribution data, chemical species concentrations and meteorological data with two source apportionment models. The source apportionment results obtained by positive matrix factorisation (PMF) and principal component analysis–absolute principal component scores (PCA–APCS) were compa...

Research paper thumbnail of Indoor air '99 - ventilation and filtration review

A general summary of the indoor Air '99 Conference held in Edinburgh in August 1999, was pres... more A general summary of the indoor Air '99 Conference held in Edinburgh in August 1999, was presented in the previous issue of Clean Air. Conferences in this series take place every three years and are the most important events in terms of gathering a large number of experts involved in various areas of lAQ. Thus, a summary of the material presented at the conference can serve as an oven/iew of the trends occurring and the directions for progress in this bro ad field internationally.

Research paper thumbnail of Investigation of the Filtration Efficiency of HEPA and ULPA Filters in Submicron Particle Size Range

High efficiency particulate (HEPA) and ultra low penetration air filters (ULPA) have been used as... more High efficiency particulate (HEPA) and ultra low penetration air filters (ULPA) have been used as filtration devices for more than fifty years. Their high efficiency makes them suitable for application in areas where clean room conditions or contamination control is required. This paper presents the results of a performance evaluation of HEPA and ULPA filters used at the Australian Animal Health Laboratory, Geelong, Victoria. A detailed description of the experimental system, test procedure, and measuring techniques is provided. HEPA and ULPA filter efficiencies were measured for both types of filters in single and tandem configurations, and for different airflow conditions. Particle counting technique and sodium flame method were applied, and the sensitivity of both techniques compared. The performance of a damaged HEPA filter was also investigated. The integrated efficiency of a HEPA filter, challenged with dry polydisperse NaCl aerosols of count median diameter 60 nm, at a flow r...

Research paper thumbnail of Vehicle emissions in Australia: From monitoring to modelling

Research paper thumbnail of Aerosol Size Distribution and Concentration in Various Units of a Children’s Hospital

Ventilation and Indoor Air Quality in Hospitals, 1996

Research paper thumbnail of Dispersion of particles by a strong explosion

The dynamics of particle transport under the influence of localized high energy anomalies (explos... more The dynamics of particle transport under the influence of localized high energy anomalies (explosions) is a complicated phenomenon dependent on many physical parameters of both the particle and the medium it resides in. Here we present a conceptual model that establishes simple scaling laws for particle dispersion in relation to the energy released in a blast, properties of the medium, physical properties of particles, and their initial position away from a blast epicenter. These dependencies are validated against numerical simulations and we discuss predictions of the model which can be validated experimentally. Other applications and extensions to the framework are also considered.

Research paper thumbnail of A comparative study of airborne particulate pollution at two bus stations of different site geography

Airborne particulate pollutant is considered to be one of the major harmful emissions produced by... more Airborne particulate pollutant is considered to be one of the major harmful emissions produced by vehicle engines as it has been directly linked to serious health problems. Passengers spend long times at bus stations and may be exposed to high concentrations of pollution. Particle pollution at two bus stations in Brisbane, Australia were monitored. The two bus stations consisted of markedly different site geography and surroundings with one situated in a street canyon and the other elevated above ground level. The same flow of traffic operated through both stations. Real time measurements of ultrafine particle concentration, size distribution and meteorological conditions were carried out on the platform continuously over several days. The results showed that the particle number concentrations were significantly different at the two stations, suggesting that the layout of site geometry and surroundings was a dominant determining factor through the injection of fresh air into the station platforms and the rates of dilution.