PARTICLE SIZE DISTRIBUTION MEASUREMENT FROM DIFFERENT

INDOOR ACTIVITIES

AUI SHWEJ HARN

Report submitted in partial fulfilment of the requirements for the award of the degree of

Bachelor of Occupational Safety and Health (Hons)

Faculty of Engineering Technology UNIVERSITI MALAYSIA PAHANG

JANUARY 2015

vi

ABSTRACT

Human exposure to particulate matter can have significant harmful effects on the

respiratory and cardiovascular system. These effects vary with number, size, and

chemical composition of particulate matter. Studying the particle size distribution under

different indoor activities can help to predict the emission and settlement of particles

with different sizes. In this research, an experimental study was carried out to

investigate the particle size distribution under different indoor activities in main office

FTeK and OSHMO. The indoor activities of office being studied were printing,

photocopying and use of air freshener sprays. Data collection was done by using laser

light scattering instrument to measure the number concentration of particles ranging

from 0.3 tm to 10 Rm. Then, the particle size distribution graph for each activity was

generated using the particle number concentration measured and particle size range.

Environmental parameters such as temperature, relative humidity, air velocity were

measured using IAQ meter. Air change rate was measured using Concentration Decay

Test Method (ASTM Standards E741-00). From the result obtained, the particle size

distribution of printing, photocopy and use of freshener spray was ranged from 0.3 tm

to 10 pm, with the predominant size range of 0.3 pm - 0.5 pm. The use of air freshener

has the highest emission rates which are 3.73 x 1010 s' at FTeK and 2.97 x 1010 s at

OSHMO. Whereas printing has the lowest emission rates, which are 3.92 x 1010 s at

FTeK and 2.63 x 1010 s at OSHMO. Significant elevation of indoor particle

concentration was noted during the three activities. The photocopy activity can be the

major source of indoor particle concentration because it emitted high number

concentration of particles within a short period and the particles remain fluctuated in the

indoor air with slow decay rate. In conclusion, the three activities selected produced

high level of submicrometer particles (< 1 pm) and indoor particle concentration is

mainly associated with the indoor activities.

vii

4BSTRAK

Pendedahan manusia kepada zarahan boleh memberi kesan buruk yang ketara pada

sistem pernafasan dan kardiovaskular. Kesan-kesan tersebut berbeza daripada segi

nombor, saiz, dan komposisi kimia bahan zarahan. Pemahaman tentang taburan saiz

zarah bawah aktiviti-aktiviti yang berbeza dapat membantu untuk meramalkan

pelepasan zarahan dengan saiz yang berbeza. Dalam projek ini, kaijian tentang taburan

saiz zarah di bawah tiga jenis aktiviti yang dijalankan di pejabat utama FTeK dan

OSHMO telah dilakukan. Tiga jenis aktiviti tersebut termasuklah mencetak, fotokopi

dan penggunaan semburan penyegar udara. Pengumpulan data dilakukan dengan

menggunakan instrumen penyerakan cahaya laser untuk mengukur kepekatan jumlah

zarah yang terdiri daripada 0.3 gm hingga 10 Rm. Kemudian, pengedaran graf saiz

zarah bagi setiap aktiviti telah dijana dengan menggunakan kepekatan jumlah zarah

diukur dan julat saiz zarah. Parameter persekitaran seperti suhu, kelembapan relative

dan halaju udara adalah diukur menggunakan IAQ meter. Kadar perubahan udara pula

diukur menggunakan kaedah ujian dalam Standard ASTM E741-00. Daripada

keputusan yang diperolehi, taburan saiz zarah mencetak, fotokopi dan penggunaan

penyegar semburan adalah dalam lingkungan antara 0.3 jim hingga 10 [Lm. 0.3 jim - 0.5

[Lm ialah size yang dominan dalam tiga jenis aktiviti tersebut. Penggunaan penyegar

udara mempunyai kadar pelepasan zarah tertinggi iaitu 3.73 x 1010 s_ I di FTeK dan 2.97

x 1010 di OSHMO. Manakala mencetak mempunyai kadar pelepasan yang paling

rendah, iaitu 3.92 x 1010 s_ I di FTeK dan 2.63 x 1010 s_ I di OSHMO. Perubahan yang

ketara bagi tahap jumlah zarah di dalam pejabat telah diperhatikan semasa tiga aktiviti

tersebut dij alankan. Aktiviti fotokopi boleh menj adi sumber zarahan utama dalam

pejabat kerana ia melepaskan jumlah zarah yang tinggi dalam masa yang singkat

dengan kadar pereputan zarah yang sangat rendah. Kesimpulannya, ketiga-tiga aktiviti

yang dipilih telah menghasilkan jumlah zarah submicrometer (< 1 jim) yang tinggi dan

tahap jumlah zarah dalam pejabat mempunyai hubungan positif dengan aktiviti-aktiviti

tersebut.

TABLLE OF CONTENTS

Page

SUPERVISOR'S DECLARATION ii

STUDENT'S DECLARATION iii

DECLARATION iv

ACKNOWLEDGEMENTS v

ABSTRACT vi

ABSTRAK vii

TABLLE OF CONTENTS viii

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF SYMBOLS xv

LIST OF ABBREVIATIONS xvi

CHAPTER 1 INTRODUCTION

1.1 Background of Study 1

1.2 Problem Statement 2

1.3 Research Objectives 3

1.4 Research Questions 3

1.5 Research Hypothesis 4

1.6 Scope of Study 4

1.7 Significance of Study 4

1.8 Operational Definitions 5

1.9 Conceptual Framework 6

viii

lx

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction 7

2.2 Physical Properties of Particle 7

2.2.1 Particle Size 7

2.2.2 Particle Size Distribution 10

2.3 Indoor Activities in Office 12

2.3.1 Printing 13

2.3.2 Photocopying

14

2.3.3 Use of Cleaning and Air Freshener Sprays

15

2.4 Formation Mechanisms of Particles from Indoor Activities 16

2.5 Particle Emission Rates Estimation

18

2.6 Health Impacts of Inhalation of Particles

20

2.7 Influence of Air Change Rate on Indoor Particle Concentrations

23

CHAPTER 3 METHODOLOGY

3.1 Introduction

25

3.2 Research Design 25

3.2.1 Study Area 26

3.3 Sampling Strategy 27

3.4 Data Collection and Instrumentation 30

3.4.1 Air Change Rate 30

3.4.2 Environmental Parameters 32

3.4.3 Particle Number Concentration and Size Distribution 32

3.4.4 Particle Mass Concentration 33

3.4.5 Estimation of Particle Emission Rate 34

3.4.6 Test Procedure for Activities Selected 35

3.5 Data Processing and Analysis 35

x

3.5.1 Descriptive Analysis 36

3.5.2 Inferential Analysis 36

3.6 Quality Assurance 36

3.7 Study Limitation 36

3.8 Study Ethics •37

CHAPTER 4 RESULT AND DISCUSSION

4.1 Introduction 38

4.2 Walktbrough Observation 38

4.3 Air Change Rate 40

4.4 Environmental Parameters 42

4.4.1 Comparison Before and After Activities 44

4.5 Particle Number Concentration and Size Distribution 46

4.6 Particle Emission Rate 50

4.6.1 Printing 51

4.6.2 Photocopy 53

4.6.3 Use of Air Freshener Spray 55

4.7 Indoor Particle Concentration of Offices 56

CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Introduction 61

5.2 Conclusion 61

5.3 Recommendation62

REFERENCES 64

APPENDICES

A Layout Design of Ground Floor of Block A2 71

BI Particle Number Concentration Based on Size Ranges During Printing

in FTeK

B2 Particle Number Concentration Based on Size Ranges During Printing

inOSHMO

B3 Particle Number Concentration Based on Size Ranges During

Photocopy in FTeK

B4 Particle Number Concentration Based on Size Ranges During

Photocopy in OSHMO

B5 Particle Number Concentration Based on Size Ranges During Use of

Air Freshener Spray in FTeK

B6 Particle Number Concentration Based on Size Ranges During Use of

Air Freshener Spray in OSHMO

C Photos Taken during Data Collection 82

D Gantt Chart 83

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w

LIST OF TABLE

Table No. Title Page

1.1 Operational Definitions 5

2.1 Particle number and surface area per 10.xg m 3 of airborne 21 particles

3.1 Description of indoor activities and its test procedure 35

4.1 Summary of information on preliminary walkthrough 39 observation

4.2 Air change rate for main office of FTeK and OSHMO 41

4.3 The temperature, relative humidity and air velocity of six 43 sampling points

4.4 Acceptable range for specific environmental parameters 44

4.5 Comparison of environmental parameters before and after 45

indoor activities

4.6 Result of ANOVA 45

4.7 Particle number concentrations based on different size range 46 (FTeK)

4.8 Particle number concentrations based on different size range 46 (OSHMO)

4.9 The emission rate for printing, photocopy and use of freshener 50

spray

4.10 Mean and standard deviation for indoor particle concentration 58

during office and lunch hours in FTeK

4.11 Mean and standard deviation for indoor particle concentration 59

during office and lunch hours in OSHMO

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LIST OF FIGURES

Figure No. Title Page

1.1 Conceptual framework of study 6

2.1 Illustration of the concept of equivalent spheres 8

2.2 Examples of particle shapes 8

2.3 Classification of particles in different size ranges 9

2.4 Particle number distributions of particles generated during 11 printing and idle mode

2.5 The volume median diameters (VMDs) during oven cooking 12 and sautéing in one home

2.6 Particulate movement and removal 17

2.7 Predicted fractional deposition of inhaled particles in human 22 respiratory tract

2.8 Indoor-outdoor ratios of (A) PM(0.02-0.1), (B) PM(1.0-05), 24 (C) PM (0.7-2.5), and (D) PM(2.5-10) versus air exchange rates measured in each home. Data are based on hourly averages

3.1 Plant layout of Faculty Technology Engineering (FTeK) 26

3.2 Plant layout of Occupational Safety and Health Management 27 Office (OSHMO)

3.3 The process flow of research 29

3.4 Measurement of air change rate in office room using gas 31 tracer methods

3.5 CO2 was released into enclosed office room with a uniform 31 concentration

3.6 IAQ meter 32

3.7 Handheld Laser Particle Counters 33

3.8 DustMate 34

4.1 Main office of Faculty Technology Engineering (FTeK) 40

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xlv

4.2 Occupational Safety and Health Management Office 40 (OSHMO)

4.3 CO2 decay rate in main office of FTeK and OSHMO 42

4.4 Comparison of particle size concentration based on different 47 size range for different activities in FTeK

4.5 Comparison of particle size concentration based on different 47 size range for different activities in OSHMO

4.6 Comparison of particle size distribution of different 48 activities in FTeK

4.7 Comparison of particle size distribution of different 49 activities in OSHMO

4.8 Comparison of particle emission rates between different 51 activities

4.9 Particle number concentration measured during printing in 52 FTeK

4.10 Particle number concentration measured during printing in 52 OSHMO

4.11 Particle number concentration measured during photocopy in 54 FTeK

4.12 Particle number concentration measured during photocopy in 54 OSHMO

4.13 Particle number concentration measured during spray in 55 FTeK

4.14 Particle number concentration measured during spray in 56 OSHMO

4.15 Indoor particle concentration variation during office and 57 lunch hours in FTeK

4.16 Indoor particle concentration variation during office and 57

lunch hours in OSHMO

4.17 Comparison of Indoor particle concentration during office 59

and lunch hours for FTeK and OSHMO

LIST OF SYMBOLS

% Percentage

> Greater than

< Less than

± Standard deviation

a Air change rate

AT Time difference

tg m 3 Microgram per cubic metre

Micrometre

.tm cm-3 Micometre per cubic centimetre

C Degree Celcius

cm-3 per cubic centimetre

cm Cubic centimetre

CO2 Carbon Dioxide

hr' per hour

L Litre

L/min Litre per minute

m s 1 Meter per second

m3 Cubic metre

rim Nanometre

s second

S Source strength or emission rate

t Time

V Volume

xv

LIST OF ABBREVIATIONS

ASHRAE American Society of Heating, Refrigerating, and Air-Conditioning Engineers

ANOVA Analysis of variance

ASTM American Society for Testing and Materials

CMD Count Median Diameter

DOSH Department of Occupational Safety and Health

FTeK Faculty of Technology Engineering

HVAC Heating, Ventilating and Air Conditioning

IAQ Indoor Air Quality

MMD Mass Median Diameter

NAAQS National Ambient Air Quality Standard

NMD Number Median Diameter

NOx Oxides of Nitrogen

03 Ozone

OH Hydroxyl radical

OSHMO Occupational Safety and Health Management Office

PSD Particle size distribution

PM Particulate matter

SOA Secondary organic aerosol

SVOC Semi-volatile organic compounds

TACs Toxic air contaminants

TSP Total suspended particle

TWA Time Weighted Average

UFP Ultrafine particle

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xvii

USEPA United States Environmental Protection Agency

VMD Volume Median Diameter

VOC Volatile organic compound

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND OF STUDY

Indoor air quality has a very strong influence on human well-being and

productivity. A study by Jenkins et al. (1992) showed that people spend 87% of their

time indoors, with only 6% outdoors, and 7% in transit. Hence, increase of indoor

pollutants is believed to increase the risks for a wide array of diseases. There is

mounting evidence that exposure to poor indoor air quality leads to excess morbidity

and mortality (Sundell, J., 2004).

The indoor environment can be further divided into microenvironments, such as

office, shopping mall, residential houses and school. The characteristics of indoor

particles can be indoor microenvironment specific (He, 2004). Many studies have

revealed the significance of indoor sources to the increase of particulate concentration.

These sources include many everyday activities, such as cleaning, printing, cooking,

smoking, burning of candles and incense sticks and even walking (Abt et al., 2000; He

et al., 2004, 2007; Hussein et al., 2006; Géhin et al, 2008; Glytsos et al., 2010). Most of

the previous researches were studying on the influence of cooking activities on the

indoor concentration in residential houses. There is still very limited information

available on the influence of office activities.

This research will focus mainly in office since office is one of the easiest places

for particles to settle and accumulate. Various electronic equipments such as printers,

photocopy machines, computers and typing machine are widely used in offices and they

are a potential source of indoor pollutants, producing a variety of particle emissions

2

(Lee et al., 2001; Kaji et al., 2007). It is also important to note that the smaller and

larger particles in the air behave differently (He, 2004). In addition to the penetration of

pollutants from outdoor air, most indoor built environments contain air pollution

sources that release fibers, particles, organic vapours, or inorganic gases (He et al.,

2007).

From the previous studies, it showed that the major sources of indoor pollutants

in office are generated from photocopier, printers and air freshener spray. According to

He et al. (2007), the monitoring of particle characteristics in a large open-plan office

showed that particles generated by printers can significantly affect the submicrometer

particle (< 1 [tm) number concentration levels in the office. Besides that, fine particles

were detected (< 1 tm) in the study of Afshari et al. (2005) during the use of air

freshener sprays. Though specific printer-emitted VOCs and PM has been studied (Kagi

et al., 2007), no information on the size distribution of the photocopier-emitted particles

has been reported. Field studies on the impact of photocopiers and printers on indoor air

quality are still relatively limited.

Furthermore, this research focused more on the particle number concentration

and distribution of different indoor activities. This is due to the existing database is very

limited to particle mass concentration and emission rates with only a few studies

reported on particle number concentration. However, since the smaller particles can be

high in number but contribute very little to mass, and they have higher probability of

penetration into deeper parts of human respiratory tract, they should be getting more

attention from researchers. Recent studies have also suggested that the particle number

concentration would be a more appropriate predictor of health impact than mass

concentration.

1.2 PROBLEM STATEMENT

Human exposure to particulate matter can have significant harmful effects on the

respiratory and cardiovascular system. These effects vary with number, size, and

chemical composition of particulate matter, which vary significantly with space and

time (Davidson et al., 2005). The PM concentration during indoor activities can reach

3

elevated values (up to tenfold compared to the situation without the sources) for short or

even for longer periods of time (Wallace, 2006). Since particle size determines the fate

of particles on or in the human body which in turn affects a person's exposure risk, it is

necessary to fully understand the size distribution of particles when determining

secondary exposure.

Hence, in this research, several indoor activities in an office were studied in

order to provide size-specific particle number distribution. This is important because

particulate matter of different sizes is known to cause different levels of adverse health

impacts to human. Finer particles penetrate into deeper parts of the human body and

cause respiratory or cardiovascular disorders (Jimoda, 2012).

1.3 RESEARCH OBJECTIVES

The aim of the study intends to meet the objectives below:

i. To investigate the particle size distribution under different indoor activities;

ii. To evaluate the relationship between different indoor activities and

indoor particle concentration level.

1.4 RESEARCH QUESTIONS

This research is further guided by the research questions below with the purpose

to gain better understanding of the research based on the identified research objectives.

The two research questions are as follows:

i. How is the particle size distribution under different indoor activities?

ii. Is there any relationship between indoor activities and indoor particle

concentration levels?

4

1.5 RESEARCH HYPOTHESIS

This study is guided by the following hypothesis:

Hoi: There are no particles of different sizes emitted during different indoor

activities in different proportion.

Hu: There are particles of different sizes emitted during different indoor

activities in different proportion.

1102: There is no relationship between indoor activities and indoor particle

concentration level.

H12: There is a relationship between indoor activities and indoor particle

concentration level.

1.6 SCOPE OF STUDY

A continuous real time monitoring measurement was conducted in offices.

Number of occupants, presence of HVAC system, models of printer, photocopier and

air freshener sprays were recorded. Particle size distribution of particles ranging from

0.3jim to 1 Ojim under different indoor activities in the office was investigated to

identify number concentration of particles with different sizes. The indoor activities

being studied were printing, photocopying and use of air freshener sprays. The particle

size distribution of these activities will be compared to find out which activity produce

the highest level of submicrometer particles (< 1 tm). Hence, we could predict the

exposure risk of office workers during different indoor activities.

1.7 SIGNIFICANT OF STUDY

Indoor sources have been identified as a major contributor to the increase of

particle concentration in indoor environment. Focusing on the particle size distribution

of particle is very important for a number of reasons. Size has a major influence on the

settling velocity of particles. Studying the particle size distribution under different

indoor activities can help to predict the emission and settlement of particles with

different sizes.

5

By understanding the particle size distribution of different indoor activities, we

could compare which activities involved the submicrometer particles that have high

impact on human health. This helps to identify the exposure risk so that preventive

measures and action plan could be developed to reduce the risk. In addition, the

information gained in this study can be used as a reference in the future studies which

related to indoor air quality. This can help to further improve the safety and health

system and parameters in the workplace.

1.8 OPERATIONAL DEFINITIONS

Table 1.1: Operational Definitions

Term used Definition

Particle size A list of values or a mathematical function that defines the

distribution relative amount, typically by number or mass, of particles

(PSD) present according to size (Jillavenkatesa et al., 2001). In this

study, particle size range is expressed in terms of aerodynamic

diameter, the diameter of a sphere of unit density (1 g cm-3)

having the same settling velocity. The particles measured were

ranged from 0.3-10 vim.

Particulate Also known as particle pollution or PM, is a complex mixture of

matter extremely small particles and liquid droplets (U.S. EPA, 2013)

Coarse Particles which are larger than 2.5 tm and smaller than 10 pm

particles in diameter (U.S. EPA, 2013).

Fine particles Particles which have an aerodynamic diameter of 2.5 tm or

less. It is usually known as PM2.5 (U.S. EPA, 2013).

Indoor The indoor activities involved in this study are mainly based on

activities the office activities conducted during office hour, which

including printing, photocopy and use of air freshener spray.

1.9 CONCEPTUAL FRAMEWORK

Figure 1.1 illustrates the variables and parameters in this study. It describes that particle

size distribution of different indoor activities are dependent on a few factors.

Particle Size Distribution I Printing

Particle Measurement Indoor _____ Photocopying number from Different L activities concentration

Indoor Use of sprays __________

Particle mass Activities

concentration

Environmental Particle Properties Parameters

Air change rate Particle size

Relative humidity I H Particle size distribution

1--', Particle shape

Air velocity

Temperature LJ Chemical composition

LEGEND

Variables being studied

Variables not being studied

Figure 1.1: Conceptual framework of study

CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

This chapter reviews the relevant literature that related to my study such as the

definition of particle properties and the description of three main indoor activities in

office which have been selected in this research. It also provides a solid historical

background to support this study. The strengths and weakness from relevant studies will

serve as a stepping stone to achieve the objectives of current research.

2.2 PHYSICAL PROPERTIES OF PARTICLE

The behaviour of particulate matter is often dominated by the physical properties of

particles. There are a few important physical properties of particles to measure. These

include particle size, particle -shape, surface properties, charge properties and

microstructure. For this research, particle size distribution is the main characteristic to

be studied. Hence, the focus will be placed on the most significant and easy to measure

property, which is particle size.

2.2.1 Particle Size

By far the most important physical property of particulate matter is particle size.

Particles are 3-dimensional objects, and they cannot be fully described by a single

dimension such as a radius or diameter unless they are perfect spheres (e.g. emulsions

8

or bubbles). Hence, it is usually convenient to define the particle size in term of

equivalent spheres concept in order to simplify the measurement process.

Sphere of same minimum length

Sphere of same

wn

w

weight

Sphere having same sedimentation rate d

Sphere of same

Sphere passing same surface area

sieve aperture

Figure 2.1: Illustration of the concept of equivalent spheres

Source: A Basic Guide to Particle Characterization (2012)

Spherical (e.g. fly h)

Aggregates Irregular

(e.g. soot) (e.g. minor)

owe

Shape

odlt Fibrous

Ce.Q. tai) (e, . cellulose)

Platelet (e. g. mke

4* Figure 2.2: Examples of particle shapes

Sphere of same maximum length

SLSphere of same

volume

Souce: Valliappan (2010)

As shown in Figure 2. 1, particle size is defined by the diameter of an equivalent

sphere which has the same property as the actual particle such as mass or volume. The

equivalent sphere concept works well for particles with regular shape. However, it may

not always be appropriate to apply on particles with irregular shape due to significant

difference in size dimension. In fact, the atmospheric particles could have different

shapes and densities, as shown in Figure 2.2 (Valliappan, 2010).

Different terminologies have been used to define the particles in various size

ranges. Total Suspended Particles (TSP) refers to all particles suspended in the air,

while PMio and PM2.5 are airborne particulate matter equal to or smaller than 10 and 2.5

tim, respectively. At least one of these three type of particulates is included as part of

indoor air quality guidelines in most countries around the world. These particle

parameters are therefore important from a regulatory standpoint. For research purposes,

airborne particles are also classified as super-coarse (> 10 jim), coarse (2.5- 10 jim), fine

(<2.5 tm), ultrafine (<0.1 pm), and nanoparticles (<0.05 jim). Identification of PM

can also be based directly on their sizes, for example, supermicrometer and

submicrometer particles denote those larger and smaller than 1 jim, respectively. Figure

2.3 summarizes the common terminologies used to describe particles of different

aerodynamic diameters and their corresponding size ranges.

Particle diameter, Dp (pm)

iO 1012 10 Up, 10' 10 I I I I I III I i i I UI I I I I UI 1111

Total suspended pakIcs(1) I (PM

PM2.5 or Fine particles Coarse SupErcoarse

Luitrafine particles (UFPs

Nanoparticles J [ubkrthneLr parlides - 1superrn1crornerprUcIesl

Figure 2.3: Classification of particles in different size ranges

10

2.2.2 Particle Size Distribution

Measurement of particle size distributions is routinely carried out across a wide

range of industries and is often a critical parameter in the industrial and non-industrial

buildings. Measuring particle size and understanding how it is distributed during

different indoor activities is important to determine the potential health risk exposure to

the occupants (Morawska and Salthammer, 2003).

Particles suspended in the air are ranged in size from about 1 nm to about 100

tm. The former is molecular size and the latter is the size above which particles

sediment rapidly due to gravitational forces. Almost all sources generate particles with

some distribution of the sizes (polydisperse aerosol) rather than particles of a single size

(monodisperse aerosol). The spread of the particle size distribution is characterized by

an arithmetic or geometric (logarithmic) standard deviation. The most common ways of

characterizing a particle distribution are in terms of its mean size, which is the average

of all sizes, its median size, which means that there are an equal number of particles

above and below this size, or its mode size, which is the size with the maximum number

of particles. The terms used include: count median diameter (CMD), number median

diameter (NMD) or mass median diameter (MMD) respectively (Morawska and

Salthammer, 2003).

The particle size distribution is always presented in either a frequency

distribution curve, or a cumulative (undersize) distribution curve. Particles generated by

most sources have a log-normal size distribution, which means that the particle

concentration versus particle size curve is "normal" (bell-shaped) when the particles are

plotted on a logarithmic scale. Geometric standard deviation characterizes the width of

the peak in the distribution. When a single pollution source is investigated and when it

operates under steady conditions (for example, steady parameters for a combustion

process), the size distribution obtained is likely to have one distinctive peak and

sometimes additional, usually much smaller peaks. These peaks are called modes of the

distribution. Different emission sources are characterized by different size distributions

and while these distributions are not unique to these particle sources alone, the

information from the size distribution can help to identify their contribution to particle

I

concentrations in ambient air, and also serve as a source signature (Morawska and

Salthammer, 2003).

Particle distributions can be presented either in terms of number or mass

distributions. In terms of number, the vast majority of airborne particles are in the ultra-

fine range. Different sources contribute to the generation of particles in the

submicrometer range, which is predominant in particle number, and different sources to

larger particles, which predominate in mass. For example, measurements of particle

concentrations as a function of time conducted in a large office building with

mechanical ventilation, air-conditioning, and sealed windows, demonstrated that for the

three smaller particle size bins of 0.3-0.5 jim, 0.5-0.7 jim, and 0.7-1.0 jim, the particle

number concentrations decrease under most conditions by roughly an order of

magnitude as the particle size bin increases one step (Fisk et al., 2000). Figure 2.4

presents an example of number distributions of particles generated during printing and

idle mode.

L2OE+05

IOOE+05 -Q- Before printing

8-OOE+04I-W-after90page pnnt

600E+04 0

400E+04 - C 0 U

200E+04

0.00E+O010 100 1000

Particle size (nrn)

Figure 2.4: Particle number distributions of particles generated during printing and

idle mode

Souce: Valliappan (2010)