Atmospheric Environment 41 (2007) 5224–5235 The effects of electric fields on charged molecules and particles in individual microenvironments K.S. Jamieson a, , H.M. ApSimon a , S.S. Jamieson a , J.N.B. Bell a , M.G. Yost b a Centre for Environmental Policy, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, UK b Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, Box 357234, Seattle, WA 98040, USA Received 21 February 2006; received in revised form 13 November 2006; accepted 5 February 2007 Abstract Measurements of small air ion concentrations, electrostatic potential and AC electric field strengths were taken in an office setting to investigate the link between electric fields and charged molecule and particle concentrations in individual microenvironments. The results obtained indicate that the electromagnetic environments individuals can be exposed to whilst indoors can often bear little resemblance to those experienced outdoors in nature, and that many individuals may spend large periods of their time in ‘‘Faraday cage’’-like conditions exposed to inappropriate levels and types of electric fields that can reduce localised concentrations of biologically essential and microbiocidal small air ions. Such conditions may escalate their risk of infection from airborne contaminants, including microbes, whilst increasing localised surface contamination. The degree of ‘‘electro-pollution’’ that individuals are exposed to was shown to be influenced by the type of microenvironment they occupy, with it being possible for very different types of microenvironment to exist within the same room. It is suggested that adopting suitable electromagnetic hygiene/productivity guidelines that seek to replicate the beneficial effects created by natural environments may greatly mitigate such problems. r 2007 Elsevier Ltd. All rights reserved. Keywords: Air ions; Electric fields; Microbes; Charged ultrafine particles 1. Introduction The nature of the electromagnetic environments that most humans are now regularly exposed to has changed dramatically over the past century and often bears little resemblance to those created in nature. In particular, the increased masking/shield- ing of individuals from beneficial types of natural electromagnetic phenomena, the presence of syn- thetic materials that can gain strong charge and increased exposures to inappropriate electric field levels and polarities have greatly altered the electromagnetic nature of the microenvironments many individuals usually occupy. Considerable electrostatic and alternating current (AC) electric fields, poor specification of materials and relative humidity (RH)/dew-point tempera- ture levels, ‘‘Faraday cage’’-like conditions plus failure to appropriately ground conductive objects ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2007.02.050 Corresponding author. Tel.: +44 20 7594 9263; fax: +44 20 7594 9334. E-mail address: [email protected](K.S. Jamieson).
Transcript
ARTICLE IN PRESS
1352-2310/$ - se
doi:10.1016/j.at
�Correspondfax: +4420 759
E-mail addr
(K.S. Jamieson
Atmospheric Environment 41 (2007) 5224–5235
www.elsevier.com/locate/atmosenv
The effects of electric fields on charged moleculesand particles in individual microenvironments
aCentre for Environmental Policy, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, UKbDepartment of Environmental and Occupational Health Sciences, School of Public Health,
University of Washington, Box 357234, Seattle, WA 98040, USA
Received 21 February 2006; received in revised form 13 November 2006; accepted 5 February 2007
Abstract
Measurements of small air ion concentrations, electrostatic potential and AC electric field strengths were taken in an
office setting to investigate the link between electric fields and charged molecule and particle concentrations in individual
microenvironments. The results obtained indicate that the electromagnetic environments individuals can be exposed to
whilst indoors can often bear little resemblance to those experienced outdoors in nature, and that many individuals may
spend large periods of their time in ‘‘Faraday cage’’-like conditions exposed to inappropriate levels and types of electric
fields that can reduce localised concentrations of biologically essential and microbiocidal small air ions. Such conditions
may escalate their risk of infection from airborne contaminants, including microbes, whilst increasing localised surface
contamination. The degree of ‘‘electro-pollution’’ that individuals are exposed to was shown to be influenced by the type of
microenvironment they occupy, with it being possible for very different types of microenvironment to exist within the same
room.
It is suggested that adopting suitable electromagnetic hygiene/productivity guidelines that seek to replicate the beneficial
effects created by natural environments may greatly mitigate such problems.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: Air ions; Electric fields; Microbes; Charged ultrafine particles
1. Introduction
The nature of the electromagnetic environmentsthat most humans are now regularly exposed to haschanged dramatically over the past century andoften bears little resemblance to those created innature. In particular, the increased masking/shield-
e front matter r 2007 Elsevier Ltd. All rights reserved
ing of individuals from beneficial types of naturalelectromagnetic phenomena, the presence of syn-thetic materials that can gain strong charge andincreased exposures to inappropriate electric fieldlevels and polarities have greatly altered theelectromagnetic nature of the microenvironmentsmany individuals usually occupy.
Considerable electrostatic and alternating current(AC) electric fields, poor specification of materialsand relative humidity (RH)/dew-point tempera-ture levels, ‘‘Faraday cage’’-like conditions plusfailure to appropriately ground conductive objects
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(including humans), can create highly localisedincidents of electromagnetic pollution capable ofsignificantly reducing concentrations of biologicallyvital and microbiocidal small air ions (SAI), suchas charged oxygen. Evidence (Ghaly and Teplitz,2004; Altmann, 1974, 1969; Barron and Dreher,1964; Lang, 1972a, b; Kritzinger, 1957) indicatesthat if the body is exposed to poorly designedelectromagnetic environments it is more prone todemonstrate reduced activity levels, oxygen uptakeand performance, whilst potentially increasingstress and likelihood of succumbing to degener-ative illnesses. Research by Cohen et al. (1998)also suggests that in certain instances electromag-netic pollution can increase the body’s alveolarburden of potentially harmful particulate matter byenhancing retention rates of contaminants wheninhaled.
2. Background
2.1. Charged molecules (small air ions)
These are also known as fast air ions or clusterions and are charged gaseous molecules that canpossess complex geometries. Negative cluster ionsare 0.36–0.85 nm in size with mobilities of1.3–3.2 cm2V�1 s�1, whilst positive cluster ions are0.85–1.6 nm in size with mobilities of0.5–1.3 cm2V�1 s�1. Their average lifetime is be-tween 50 and 250 s, depending on the aerosolcontent of the air. They have a complicated andvaried chemical nature, usually independent ofnearby aerosols, which normally changes severaltimes a second. They each possess a singleelementary charge of 1.6� 10�19 C, and theirdirection of movement is greatly influenced byelectric fields, with a large degree of attractionbeing shown towards opposite or ‘‘mirror’’ charges.They are repelled by charges of similar polarity andattracted to those of opposite polarity. Both smallnegative and small positive air ions have beenshown to be microbiocidal, further details are givenin Jamieson and Jamieson (2006). Whilst prolongedlong-term exposure to unipolar negative ionisationappears capable of shortening life-span (Kelloggand Yost, 1986), experiments by Goldstein andArshavskaya (1997), indicate that charged oxygenappears vital to life and that animals can diewithin weeks of being completely deprived of thisform of SAI.
2.2. Charged particles
2.2.1. Intermediate and large air ions
These are solid or liquid charged aerosol parti-cles/ultrafine particles. Both long- and short-termexposures to elevated concentrations of such parti-cles are associated with raised admissions tohospital and premature death. At present, they areseldom measured in air pollution or air ion studies.Intermediate air ions are 1.6–7.4 nm in size withmobilities of 0.034–0.5 cm2V�1 s�1 and are nor-mally present in far lower numbers than large airions. There are two main types of large air ions (alsoknown as slow ions because of their lower mobility).Light large air ions are 7.4–22 nm in size and havemobilities of 0.0042–0.034 cm2V�1 s�1, whilst heavylarge air ions (charged Aitken particles) are22–79 nm in size and have mobilities of0.00087–0.0042 cm2V�1 s�1. Both follow air-streamflows like uncharged aerosols unless very largeelectric fields are present. Their chemical nature issimilar to that of uncharged aerosols, and they canpossess more than one elementary charge. Increas-ing charge increases their likelihood of depositionon oppositely charged surfaces (Dolezalek, 1985).
2.2.2. Charged ultrafine particles
These are charged particles of particulate mattero0.1 mm (100 nm) in size and are classed as PM0.1.Ultrafine particles can induce greater cytotoxicityand epithelial damage than fine particles composedof similar materials, partially due to their far greatersurface area per given mass, a factor which can alsoincrease their ability to carry toxic co-pollutants.
2.2.3. Charged fine particles
These are charged particles from 0.1 to o2.5 mmin size. Electrical effects can predominate as atransport and deposition mechanism for particlesp1 mm in size (McMurry and Rader, 1985).
Particles p1 mm in size can greatly exacerbatehealth problems. In excess of 90% of PM10 particlescan be in this size range (Rao et al., 2005). Suchparticles can be composed of dust, lint, tobaccosmoke, diesel soot, fresh combustion particles,ozone and terpene-formed aerosols, nitrates andsulphates, heavy metals, mineral fines, respiratorydroplets, skin squamae and a variety of othersubstances. Airborne biological contaminants inthis size range include allergens, bacteria, fungalspores and viruses. The greater the charge theypossess the higher the likelihood of their deposition.
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2.3. Alternating current (AC) electric fields
AC fields are measured in volts per metre (Vm�1)and can be created by high-voltage power lines,electrical wiring and items of electrical equipment.They increase in strength as voltage is raised. Whilstelectrical equipment has to be switched on beforemagnetic fields are registered, electric fields can bedetected even if the equipment is switched off butnot unplugged from the mains power socket.Frequencies within the range being measured inthe present case study (10–2000Hz73 dB) can bebiologically active (Lang, 1972a, b).
2.4. Electrostatic fields
Under natural fair weather conditions an electro-static vertical potential gradient of 100–200Vm�1
can exist near the ground, with the positivelycharged ionosphere acting as an anode and theearth as a cathode causing a transfer of negativeions from the earth to the sky and positive ions fromthe ionosphere to the earth along electrostatic linesof force. When poor weather conditions, suchas thunderstorms, arise this situation is reversedand triboelectric inversion occurs, with the airbelow positively charged clouds becoming morenegatively charged than the ground underneath,causing the vertical electric current to flow in theopposite direction—in such situations fields of3000–10,000Vm�1 can be encountered (Sulman,1980; Sheppard and Eisenbud, 1977; Bach, 1967).Distorted current flow and higher fields than thiscan however be created indoors, particularly whenconditions of low RH or dew-point temperatureexist.
2.5. Standards and guidelines
2.5.1. Standards regarding air ion concentrations
The Ministry of Health of the Russian Federa-tion’s ‘Sanitary and Epidemiologial Norms’ guide-lines (SanPiN, 2003) stipulate mandatory maximumand minimum levels of bipolar air ion concentra-tions in the computer workplace. SAI concentra-tions must not be o600 negative (NSAI) and 400positive small air ions (PSAI) cm�3, and levels mustnot exceed 50,000 NSAI or PSAI cm�3. Theseregulations state that optimum recommended ionconcentrations to reduce fatigue and enhancecapacity for work are 3000–5000 NSAI and1500–3000 PSAI cm�3. These air ion concentrations
are also required to have a factor of unipolarity Y,with a minimum and maximum ratio of positive tonegative ions being given by 0.4pYp1.0.
Though the recommended optimal and manda-tory maximum small air ion concentrations sug-gested by the Russian SanPiN guidelines are farhigher than often found in nature, such levels canhelp to reduce incidences of excess charge.
Though no formal legislation appears to exist inthe western world, in the USA, the Federal AviationAuthority (F.A.A.) acknowledged that both verylow SAI concentrations, and high ion concentra-tions with a factor of unipolarity with a strongimbalance of positive air ions can produce detri-mental effects (Rosenberg, 1972).
2.5.2. Standards regarding AC fields
Whilst International Commission on Non-Ionis-ing Radiation Protection (ICNIRP, 1998) guidelinesstipulate that 60Hz AC electric fields encounteredby members of the general public should bep4200Vm�1, Russian and Swedish guidelines forcomputer users advocate AC field levels of p25 andp10Vm�1, respectively, at 0.5m from computersin the ELF 5–2000Hz (Band I) range (SanPiN,2003; TCO, 2003).
AC fields may partially influence ion deposition,coagulation rates along with localised contamina-tion levels if they are sufficiently strong.
2.5.3. Standards regarding electrostatic fields
The Russian guidelines for computer usersstipulate that the electrostatic potential at 0.5mfrom computers should be p500V (SanPiN, 2003),whilst the Swedish guidelines specify a maximumsurface potential of 7500V (TCO, 2003).
However, whilst such standards can be of greatuse in reducing incidences of electrostatic discharge,induced charge and surface contamination, they donot take into account the fact that the body appearsto function best when exposed to constant verticalelectrical fields and that exposure to distorted fieldregimes and ‘‘Faraday-cage’’ conditions may actu-ally prove detrimental to health (Jamieson et al.,2006).
2.6. Hypothesis and scientific evidence
The presence of inappropriate levels and typesof electric fields in individual microenvironmentsmay greatly reduce localised concentrations ofSAI, whilst increasing localised concentrations of
charged ultrafine particles, such as large air ions(LAI).
The possible presence of high concentrations ofLAI in the room being assessed for the case study isindicated by the fact that the air is highly conductivewhilst having low concentrations of SAI—large airions normally add little to the air’s conductivityapart from when SAI are absent (Wait andParkinson, 1951). Note: though LAI are categorisedas being p79 nm in size, electrical effects canpredominate as a transportation and depositionmechanism for ultrafine particles and fine particlesup to 1 mm in size.
3. Case study
Measurements of SAI concentrations, electro-static potential and AC electric field strengths weretaken in an office environment. It was intended thatthis work would indicate the link between inap-propriate levels and types of electric fields, lowconcentrations of SAI and high concentrations ofLAI, whilst also showing how the electromagneticenvironments individuals can be exposed to whenindoors often have little resemblance to thatgenerally experienced in nature. This work was alsoundertaken in conjunction with a critical literaturereview.
3.1. Methodology
3.1.1. Room description
The office studied was a computer work-suite,with both natural ventilation and air conditioning,which is situated in a reinforced-concrete building inBergen, Norway. Data were collected on separatedays in July 2005 whilst the main workstation wasoccupied. A listing of the materials and finishesfound in this room are given in Table 1, and a plan,section and photograph of it are shown in Fig. 1.
3.1.2. Measurement procedures
For the vertical sections created through theroom used for this work, continuous measurementswere taken at 0.1m increments from a height of2.1m to a height of 0.1m, with further readingsbeing taken 0.05m from the finished floor level ineach instance. These were taken at 0.35m intervalsalong a line that passed diagonally directly throughthe sitting area occupied by the main computeroperative and the 0.25m horizontal grid-work usedfor measuring the horizontal sections. Two hundred
and seventy-six individual sampling points wereused for constructing the vertical isopleths of thisroom, and 202 sampling points for the creation ofthe horizontal isopleths. As the measurements weretaken at grid points, it was possible to missmaximum and minimum readings that appearedoff-grid.
3.1.2.1. Ion measurements. The concentrations ofSAI present were measured using an air ion counterby Alpha Lab Inc., which had accuracy guaranteedto 725% for ions in this range (mobility40.8 cm2V�1 s�1) though the unit itself is cali-brated to an accuracy of 75%. The lowestcharacterisable mobility for the unit is0.5 cm2V�1 s�1. It had been intended to extend thiswork to include the measurement of large air ions,but this part of the project was postponed due tolack of equipment/funding.
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Fig. 1. Case study: office.
K.S. Jamieson et al. / Atmospheric Environment 41 (2007) 5224–52355228
Whilst undertaking measurements of NSAI con-centrations, a period of between 10 and 15 s wasallowed between switching grid-points before themaximum and minimum concentrations werelogged at each location. These were each taken overa minimum period of 15 s and up to a maximumperiod of 30 s in cases where large fluctuations invalues were noted. When these occurred, due to thepresence of clouds of high or low ion concentrationsin sections of poorly mixed air in individualmicroenvironments, the most regular maximumand minimum SAI concentrations noted werelogged. Due to time limitations, it was not possibleto create isopleths of PSAI concentrations, thoughspot measurements, and additional studies by theauthors (Jamieson et al., 2005), indicate that theconcentrations and distribution of this type of ionthroughout the room would have been very similarto that found with the NSAI.
3.1.2.2. AC electric field measurements. Single mea-surements were undertaken at each grid-point usingan EMFields Professional AC Electric and Mag-netic Field Metre by Perspective Scientific Ltd.,which has an expected accuracy of 4710% in the50–500Hz range and can measure from 0 to1999Vm�1, RMS, with a frequency response of10–2000Hz73 dB. The metre is calibrated forhand-held use and provides a strong indication ofthe E-fields a person would experience at thelocation being measured. A truly accurate readingcannot be achieved as perturbed electric fields varygreatly due to the presence of conductive objects,including the instrument’s operator in the environ-ment being assessed.
3.1.2.3. Electrostatic potential measurements. Mea-surements of electrostatic potential (D) were takenin the X-, Y- and Z-axis at each grid-point using aJCI Static Monitor 140F by John Chubb Instru-mentation to allow ‘‘3D-measurements’’ to beobtained. This was undertaken using the following
formula:
D ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiX 2 þ Y 2 þ Z2
p.
The monitor used to measure the electrostaticpotential had a 1 and 10V resolution, a response of�3 dB at E400Hz, and an accuracy 72% full-scaledeflection.
3.1.2.4. Additional measurements. The number andtype of measurements taken were primarily deter-mined by equipment availability and access periods.Spot checks of temperature and relative humidity(RH) variations were taken throughout the courseof the measurements. Isopleths were also created ofthe light levels measured during the course of theassessment period but are omitted from the currentdiscussion. It was not possible to measure windspeeds or air pressure variations.
4. Results and discussion
Access periods limited the amount of data thatcould be collected and the number of complete datasets that could be formed. The results shown belowin Table 2 were taken on two separate days whenthe laptop computer used on the main workstationwas grounded. There was a large variation betweenthe temperature and RH/dew-point temperaturelevels recorded indoors on these days but themeasurements taken indicated that low levels ofSAI were normally detected in areas where highelectric fields occurred. Access periods limited theamount of data that could be collected and thenumber of complete data sets that could be formed.
4.1. Air ion concentrations
4.1.1. Vertical section
Analysis of the data taken at 276 sampling pointsfor this section determined an arithmetic mean of361 negative small air ions cm�3 (SNAI cm�3), with
average maximum and minimum values of 930 and10 SNAI cm�3 being found. The lowest actual valuedetected in several areas was 0 SNAI cm�3 and thehighest value 1070 SNAI cm�3. The isopleths cre-ated from these measurements are shown in Fig. 2,which indicates that very low SAI concentrationswere found in the microenvironments where theoperative was sitting and where high electric fieldsoccurred. In the personal breathing zone of thecomputer operator concentrations of10–280 SNAI cm�3 were detected, whilst the influ-ence of inappropriate types and levels of fields onSAI concentrations was also clearly seen for theanglepoise desk-light located on grid-line 10 whereconcentrations of 0–40 SNAI cm�3 were registered.
4.1.2. Horizontal section
Measurements were taken to create horizontalisopleths at a height of 1.1m when the laptop com-puter on the main workstation was both groundedand ungrounded, though only those taken whilst it
was grounded are shown in Fig. 3. On the day thesemeasurements were taken the weather was farwarmer than when the data for the vertical ionisopleths were collected, see Table 2, necessitatingthe continual use of an oscillating fan unit withinthe room, and natural ventilation provided by anopened high-level external window, in addition tothe sporadically operating air conditioning unit.
Analysis of the data taken at the 202 samplingpoints used determined an arithmetic mean of433 SNAI cm�3 for this section, with average max-imum and minimum values of 910 and35 SNAI cm�3, respectively, being found. The low-est actual value detected was 10 SNAI cm�3 and thehighest value 1060 SNAI cm�3. The isopleths cre-ated from these measurements are shown in Fig. 3.
The measurements taken clearly indicate thatconcentrations of negative small air ions measuredin the room used for the case study were well belowthe minimum acceptable level of 600 SNAI cm�3
Fig. 3. Plan section at height of 1.1m showing concentrations of small negative air ions cm�3.
K.S. Jamieson et al. / Atmospheric Environment 41 (2007) 5224–52355230
very low concentrations of SAI are detected in themain work area, the concentrations of chargedoxygen molecules must also have been greatlyreduced.
It is suggested that the presence of inappropriatelevels and types of electric fields in individualmicroenvironments within the room may greatlyincrease both the localized concentrations ofcharged sub-micron particles, such as large air ions,in those areas and the risk of contamination andrespiratory problems.
4.2. AC electric fields
4.2.1. Vertical section
Natural vertical atmospheric fields are oftenalmost completely prohibited from entering manymodern buildings due to the type of constructionmethods used. Even if such fields had been able topenetrate the room being measured; they wouldoften have been masked by the high levels of ACelectric and electrostatic fields present that wouldhave distorted the direction of current flow.
This section was measured on the same day as thevertical isopleths showing NSAI concentrations.
The arithmetic mean for the AC fields measuredat the 276 sampling points was 20.9Vm�1, withactual maximum and minimum values of 452.0 and1.0Vm�1, respectively, being obtained. The isoplethcreated from the data collected is shown in Fig. 4,and when studied in conjunction with Fig. 2 visuallydemonstrates the link between high AC electricalfields and low SAI concentrations.
Though the AC fields emitted from the monitorscomplied with both Russian and Swedish guidelines,the fields emitted by the junction box on theworkstation and the anglepoise desk-light exceededthose suggested guidance levels for computers,thereby preventing the creation of low-field condi-tions in those microenvironments and creating highlocal concentrations of charged sub-micron parti-culates.
4.3. Electrostatic potential
4.3.1. Vertical section
This was measured on the same day as the ionmeasurements taken for the horizontal section, andis shown in Fig. 5. The average electrostaticpotential measured was 104.9V, with maximum
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1 2 3 5 6 8 9 10 11
AC E-fields V m−1
10
30
50
70
90
110
130
150
170
190
210
SECTION
V m−1
0
10
25
375
475
4 7
Fig. 4. AC electric field strengths in Vm�1.
1 2 3 4 5 6 7 8 10 11
SECTION
10
30
50
70
90
110
130
150
170
190
210
kV
-0.8
0.0
0.5
9
Fig. 5. Electrostatic potentials in kilovolts (kV).
and minimum values of 7705.8 and 2.2V also beingnoted. Field readings in excess of 500V were alsorecorded off-grid above the CRT monitor.
It can be clearly seen in Fig. 5 that theelectrostatic field in this room does not resemblefair weather field conditions and that the room’soccupant is constantly exposed to distorted currentflow regimes. It is suggested that such conditionsmay greatly reduce the operator’s biological andwork efficiency.
Moreover, the influence of tribolectric charging increating high electrostatic potentials is clearlydemonstrated in Fig. 5, with the greatest poten-tial measured in the room being created by fric-tional charging of the footrest of the computer
operative’s chair by the user (concentrations of0–40 SiNAI cm�3 being noted there). Again lowconcentrations of SAI were found where high fieldsfrom electrical equipment and wiring existed.
In addition to the electric fields created by theitems of electrical equipment and cabling in theroom, high body voltages can be created throughfrictional charging, particularly when individualswear insulative footwear, or come into contact withinsulative materials such as are often used forclothing and furnishings. The most notable cause ofthis in the room was the insulative footrest whichcurtailed charge dissipation from the computeroperative. Such charging leads to a high bodypotential being created by frictional charging and
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retention of charge, with the excess charge beingdissipated when a conductive surface is touched.The problems encountered from electrostatic char-ging in such situations are much exacerbated inwintertime when lower RH/dew-point temperatureleads to higher potentials being generated. As anexample of this, Moss (1987) showed that walkingon a floor finish similar to the one in the surveyedroom at 20% RH at 21 1C (�2.5 1C dew-pointtemperature) could generate 12,000V whilst thesame action at 80% RH at 21 1C (17.4 1C dew-pointtemperature) generated only 250V.
4.4. Temperature, RH and dew-point temperature
Indoor temperatures on the first measurement daywere 26.870.6 1C, necessitating the continual use ofan oscillating fan unit within the room, in addition tothe air conditioning unit (which was sporadically inoperation) and natural ventilation provided by theopened external window. 29.173.6% RH was alsorecorded during that period, giving an average dew-point temperature of 7.35 1C. On the final measure-ment day the temperature was 19.370.3 1C, with66.774.2% RH (12.96 1C dew-point temperature).The air conditioning was still in sporadic operation,though the fan was no longer in use and the externalwindow shut.
Furthermore, large seasonal variations can occurwith regard to charge generation in buildings, withhigher charges generally being generated in wintermonths (even when external RH levels are 450%).This is primarily due to the reduction in indoor RHlevels due to the operation of heating systems withRH being halved for every 10 1C increase intemperature over the outdoors. Vonnegut (1973)noted that in a hypothetical situation where 100%RH was encountered at �20 1C, indoor tempera-tures of 20 1C would reduce RH to o10%. Lowhumidities can greatly increase the deposition andretention of contaminants as they encourage thegeneration of higher electric fields.
5. Effects of electrostatic and AC electric fields on
charged molecules and particles
Both fair weather and poor weather field condi-tions can significantly influence biological processes,with poor-weather fields tending to be seen asdetrimental and fair weather fields beneficial.Building occupants can often be screened fromthese however due to many buildings acting like
Faraday cages. Constant vertical electrostatic fieldscan significantly influence a number of physiologicalparameters in comparison to controls under Fara-day conditions. These include breathing rate,oxygen uptake, activity levels and immune systemfunctioning (Mose and Fischer, 1975; Altmann,1974, 1969; Lang, 1972a, b; Kritzinger, 1957; Hahn,1956). It is suggested by the present authors thatexclusion and/or masking of individuals from suchphenomena, or artificial simulations of them, maysignificantly influence their health, performance andwell-being.
In indoor environments where large concentra-tions of aerosols exist, the main cause of decay ofSAI can be collision with neutral or oppositelycharged particles. When this occurs, the result of thecollision can be the creation of an intermediate orlarge air ion. SAI can also be lost due to plate-outon surfaces, this situation being greatly exacerbatedwhen the surfaces themselves obtain a highdegree of charge and when there is o20–30% RH.As previously mentioned, high electric fields canalso be created from electrical items and wiring,and through frictional charging, as was demon-strated by the measurements taken next to thefootrest of the computer operative’s chair in thispresent study.
Recombination of oppositely charged cluster ionsin the air can additionally occur and result in theirneutralisation, though this is more likely to occur inareas where there is little aerosol pollution. Highlevels of unipolar charge in particular, such as arenoted in the case study, can affect the concentra-tions of different sizes of aerosols, with dropletdisintegration occurring when the repellent forcesthat unipolar charges apply to each other exceed thedroplet’s surface tension, causing the creation ofsmaller particles (Wehner, 1969). Such situationsmay further exacerbate contamination and healthrisks by creating higher concentrations of chargedultrafine particles. Excess electrical charges mayoften play a key part in contamination incidences bysignificantly increasing the coagulation, chargingand deposition of microbes, contaminated airbornedroplets and particulate matter on the skin,surroundings and airways of those exposed. Thegreater the degree of charge that such contaminantsreceive, the greater the likelihood of infection andcontamination, as high electric fields can alsosignificantly raise the deposition velocity andlocalised deposition rate of charged and charge-neutralised dielectric particles p1 mm in diameter.
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This is because increased potential linearly increasestheir deposition onto oppositely charged objects.
As demonstrated in the case study, high electricalfields can often be created in everyday life. Thepresence of inappropriate charging regimes inindividual microenvironments may greatly increaseincidences of skin and surface contamination andthe likelihood of contaminants, including patho-gens, being retained by the body when inhaled,though there are many ways in which excess chargecan be reduced (Jamieson et al., 2006).
Past research by Wedberg (1991, 1986, 1987)found that in office environments the deposition ofparticulate matter 40.07mm in size on individuals’faces was significantly influenced by electrical fieldregimes, with precipitation rates increasing markedlyas the magnitude of applied voltages increased—facial deposition rates of E100particlesmm�2 h�1 at0 kV increasing to E1000particlesmm�2 h�1 whenthe body was charged to a potential of 75–6kV.This is because though such particles have driftvelocities far lower than normal indoor (and out-door) wind velocities, they are likely to be capturedwhen passing sufficiently close to suitably chargedsurfaces. High charging will also increase contami-nant deposition onto other areas of exposed skin,such as the hands, thereby increasing the risk ofcontamination spread. Research by Rao et al. (2005)indicates that 490% of airborne particles may beo1mm in size. Electrostatic attraction betweenairborne ultrafine particles and charged surfaces isoften a greater determinant of localised contaminantdeposition than aerodynamic forces or gravity.Unlike gas molecules and millimetre-sized mole-cules, aerosols strongly adhere to surfaces theycontact (Hinds, 1999; Yost and Steinman, 1986).
Electrical forces can greatly increase the deposi-tion of charged particles in the respiratory tractsince whilst its surface, is uncharged, it is electricallyconductive, and when a suitably charged particleapproaches the alveolar surface the particle inducesan image charge of opposite polarity on its surface,thereby attracting the particle. Work by the Inter-national Commission on Radiological Protection(ICRP, 1994) modelling particle deposition in therespiratory tract indicates that maximum alveolardeposition in humans may occur with singletultrafine particles of approximately 20 nm(0.02 mm) diameter. Research by Cohen et al.(1998) has indicated that this size of particle whensingly charged may deposit 5.370.3 times morereadily than uncharged particles, and 3.470.3 times
more readily than charge-neutralised particles.Creating conditions where such particles gaincharge may greatly increase risk of infection andrespiratory problems.
6. Conclusions
The measurements discussed within this docu-ment, and taken during additional surveys by themain author, indicate that many individuals mayspend the majority of their time indoors in ‘‘Fara-day cage’’-like conditions exposed to (unnecessarily)high electrostatic and AC electric fields. Suchconditions can reduce available concentrations ofbiologically-essential SAI, whilst increasing theirlikelihood of inhaling and retaining airborne con-taminants, such as charged ultrafine particles andbeing exposed to higher levels of difficult-to-removesurface contamination. The degree of ‘‘electro-pollution’’ that individuals are exposed to is verymuch determined by the type of microenvironmentthey occupy, with inappropriate levels and types ofelectric field normally resulting in low concentra-tions of SAI and high concentrations of LAI. Veryoften, different types of microenvironment can existwithin the same room, with the location occupied byindividuals for prolonged periods greatly influen-cing the levels of pollution they are exposed to.Therefore, where possible, future research studyingthe link between particulate pollution and healthshould include measurements of concentrations(and charge) of small, intermediate and large airions and sub-micron particles in such areas.
The cost to national economies of poor indoorair/indoor environmental quality (IAQ/IEQ) prac-tices is immense and may be significantly reduced byintroducing suitable electromagnetic hygiene/pro-ductivity guidelines. It was estimated by Mendellet al. (2002) that respiratory illnesses due to poorbuilding management and practices in the USAalone may cost $32 billion dollars annually in termsof absenteeism, health-care costs and reduced workefficiency, whilst Clements-Croome and Baizhan(1997) suggest that improving indoor air qualitymay increase the productivity of office staff byE10%. It is suggested by the current authors thatcreating indoor environments which more closelyenhance/simulate beneficial natural electromagneticphenomena and reduce incidences of excess charge,whilst exposing individuals to constant verticalelectrical fields and suitable concentrations ofbalanced bipolar small air ionisation, may greatly
ARTICLE IN PRESSK.S. Jamieson et al. / Atmospheric Environment 41 (2007) 5224–52355234
improve their productivity and biological function-ing at the same time as significantly reducingincidences of contamination and infection. Furtherresearch in this relatively unexplored area isurgently required.
Acknowledgements
Special thanks are given to assistant professorAlvhild Allette Bjørkum of Bergen UniversityCollege, Norway and professor Karen Rosendahlof Haukeland University Hospital, Norway fortheir generous help, advice and assistance inconducting this research. The authors would alsolike to thank Dr. Roy N. Colvile and Dr. DominicWeiss of Imperial College London for theirassistance during the course of this work.
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