Environ. Sci. Technol. 2010, 44, 526–531
Corona Ions from Overhead Transmission Voltage Powerlines: Effect on Direct Current Electric Field and Ambient Particle Concentration Levels FOLASADE J-FATOKUN,† ROHAN JAYARATNE,† L I D I A M O R A W S K A , * ,† D A V I D B I R T W H I S T L E , ‡ RIHANDANU RACHMAN,‡ AND KERRIE MENGERSEN§ ILAQH, School of Engineering Systems, and School of Mathematical Sciences, Queensland University of Technology Brisbane, GPO Box 2434, Brisbane 4001, Australia
Received August 6, 2009. Revised manuscript received October 28, 2009. Accepted November 8, 2009.
Along with their essential role in electricity transmission and distribution, some powerlines also generate large concentrations of corona ions. This study aimed at the comprehensive investigation of corona ions, vertical direct current electric field (dc e-field), ambient aerosol particle charge, and particle number concentration levels in the proximity of some high/ subtransmission voltage powerlines. The influence of meteorology on the instantaneous value of these parameters and the possible existence of links or associations between the parameters measured were also statistically investigated. The presence of positive and negative polarities of corona ions was associated with variation in the mean vertical dc e-field, ambient ion, and particle charge concentration level. Though these variations increased with wind speed, their values also decreased with distance from the powerlines. Predominately positive polarities of ions were recorded up to a distance of 150 m (with the maximum values recorded 50 m downwind of the powerlines). At 200 m from the source, negative ions predominated. Particle number concentration levels, however, remained relatively constant (103 particle cm-3), irrespective of the sampling site and distance from the powerlines. Meteorological factors of temperature, humidity, and wind direction showed no influence on the electrical parameters measured. The study also discovered that e-field measurements were not necessarily a true representation of the ground-level ambient ion/ particle charge concentrations.
1. Introduction High-voltage overhead powerlines (HVPLs) are essential to the process of power transmission and distribution, as they are used to transfer electricity from the generating stations to other stations, substations, and the end user at a much reduced voltage. But despite this essential role, some powerlines also generate large concentrations of corona ions * Corresponding author phone: +617 3138 2616; fax: 3138 9079; e-mail:
[email protected]. † ILAQH. ‡ School of Engineering Systems. § School of Mathematical Sciences. 526
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when the conductor’s surface electric field (e-field) gradient exceeds a certain critical voltage value referred to as the onset voltage for corona discharge. This onset voltage depends on a number of factors, including the conductor’s surface irregularity (particle deposition, presence of protrusions, contaminations, etc.), conductor characteristics (diameter, age, etc.), the voltage transmitted, the number of subconductors used for the transmission, and the prevailing meteorology (1-4). The release of large concentrations of corona ions (i.e., molecular oxygen, nitrogen, and free electrons) into the ambient air by HVPLs is associated with variation in the earth’s natural direct current (dc) e-field of about 100 V m-1, and this effect is measurable at ground level (5-7). In the first 100 ns of their release, corona-generated ions attach to aerosol particles in the air to form atmospheric or small ions. The small ions later interact with other ambient aerosol particles by the attachment of ions to aerosols and the transfer of charge from the former to the latter causes the aerosols to increase their charge state (8-10). These charged particles are then carried by the wind, and depending on the prevailing wind speed and turbulence, their presence is observed several hundred meters from the ion -emitting source (11). Over the years, various studies have been conducted on corona emission by HVPLs, their effect on the earth’s natural dc e-field (9-12), and their impact on atmospheric chemistry (13-15) and the biological system (12, 13). However, to date no study has simultaneously characterized air ion concentration, particle charge concentration, particle number concentration, and variation in magnitude of the vertical dc e-field, while also investigating possible links/associations between these various parameters in the environment of energized power conducting lines. Being a novel study to be conducted in the proximity of overhead HVPLs, this study provides more understanding of the localized effect of corona ions generated by transmission voltage powerlines. The aim of the study was to investigate the effects of corona ions generated by overhead powerlines on the magnitude of the local dc e-field, net ambient ion concentration, ambient aerosol particle number, and particle charge concentration levels. The main objectives were to quantify parameters directly under the HVPLs and as a function of distance from the HVPLs, while also investigating the possible effect of meteorology (wind speed, wind direction, temperature, pressure, air humidity, and solar radiation) on the instantaneous value of these measured parameters. Regression and multivariate analysis were used to statistically investigate the existence of possible associations between measured parameters.
2. Methods This study was conducted between February and December 2006 at three different locations, in the proximity of some energized overhead high transmission voltage powerlines (HTVPL; voltages of 220-330 kV) and subtransmission voltage powerlines (STVPL; voltages of 110-132 kV). However, the operating characteristics of these lines such as the actual operating voltage and the peak current during measurements were not known. Due to the nature of the parameters investigated and especially as certain environmental conditions were already known to be unsuitable for the operation of some of the instruments used, all the samplings were carried out under strictly desired meteorology of very fine weather (clear skysno rain or any form of precipitation that may reduce ambient particle concentration and no electrified rain cloudssas this can also affect the magnitude and sign 10.1021/es9024063
2010 American Chemical Society
Published on Web 12/02/2009
of the dc e-field). The desired wind speeds during sampling were slight to moderate. The predominant wind direction must be from the powerlines to the receptors (instruments), and the air humidity must be less than 70% for reliable operation of the aerosol electrometer (since its zero reading drifts uncontrollably at high humidity values, causing the instrument to be unstable and its output unreliable (14). The methodology employed also involved quantifying parameters as a function of distance (i.e., directly under and some distance away) from the powerlines. 2.1. Measurement Site. The main criteria for selecting suitable sampling sites were flat topography, open terrain, and the absence of interfering trees and buildings. It was also ensured that vegetation was less than 1 m in height. On the basis of this criteria, three different powerline sites (referred to in this study as A, B, and C) were selected. Site A had two overhead double circuit alternating current (ac) HTVPLs and one overhead double circuit STVPL running through its entire length and site B had an overhead double circuit ac HTVPL and an overhead double circuit ac STVPL, while site C had one overhead double circuit ac HTVPL. At sites A and B, measurements were conducted at distances of less than 10 m from the lines. At site C, the availability of large perpendicular space on both sides of the HTVPL provided the opportunity for measurements to be conducted directly under the lines and as a function of distance (upwind and downwind) from the lines. At this location, the sampling instruments were placed at distances of between 50 m in the upwind direction to 200 m in the downwind direction of the lines. Consequently, while adhering strictly to the preferred meteorological conditions for sampling, a total of 16 days of sampling was carried out in this study (10 days at site A, 3 days at site B, and another 3 days at site C). 2.2. Instrumentation. The real-time monitoring of total aerosol particle number concentration in the air environment of the powerlines was carried out using a portable TSI model 8525 P-Trak ultrafine particle counter (P-Trak). Designed for sampling ambient aerosol particles within the size range of 0.02-1 µm, the P-Trak is also equipped with in-built memory for data storage (15). The TSI model 3068 aerosol electrometer (AE) used to measure net particle charge concentration was designed for sampling 0.002-5 µm sized particles (16). The suitability, limitations, and optimal operating conditions of using AE for ambient particle charge measurement was established in a separate study (14). Factory-calibrated AlphaLab air ion counters (AIC) with a field measurement range of 10-106 ions cm-3 and minimum detectable ion size of 1.6 nm were used for measuring the net ambient ion (space charge) concentrations in the environment of the powerlines. Local vertical dc e-field was measured using JCI 140 e-field meters. These field meters have resolutions of 10 V m-1 and were designed for a field measurement range of ( 20.000 V. Prior to being used for any measurement, the e-field meters were precalibrated in the laboratory using two flat parallel plates connected to a variable voltage supply to simulate a known electric field. The prevailing meteorology (i.e., wind speed, wind direction, temperature, solar radiation, humidity, and pressure) during sampling was recorded with an automated Monitor Sensors weather station. Apart from the P-Trak and weather station, which both had in-built memory for data storage, the output signal of all the other instruments were digitized and transmitted onto a computer via a wireless system of data transfer. 2.3. Measurement Techniques and Design. The techniques employed were to conduct sampling (i) directly under and at distances of less than 10 m from the lines and (ii) as a function of distance (greater than 10 m in the upwind and downwind directions) from the lines. Since the earth’s fair weather dc e-field is subject to variation with location and even under nonthunderstorm conditions (17), prior to each
sampling the natural (i.e., background) dc e-field in the same locality as the powerlines (but well away from any electrical infrastructure, buildings, or trees) was always measured. The average value of these background measurements was of the positive polarity (i.e., e-field directed vertically downward) and around 70 V m-1. 2.3.1. Measurements at Distances Less Than 10 m. Site A. The parameters measured at this site were the magnitude of the vertical dc e-field, net ambient ion concentration, net ambient aerosol particle charge concentration, and ambient aerosol particle number concentration. At this location, the AE, P-Trak, and meteorological station were placed at a fixed position of 5.8 m downwind (D5.8) of the STVPL, while the AIC (AIC1 and AIC2) and e-field meters (Ef1 and Ef2) were placed 4 m downwind (D4) of the lines (Figure S1a, Supporting Information). Site B. The parameters measured at site B were the vertical dc e-field, net ambient aerosol particle charge concentration, and ambient aerosol particle number concentration. At this site, one e-field meter (Ef1) was placed between the HTVPL and the STVPL at a position labeled as L00, while the AE, P-Trak, and a second e-field meter (Ef2) were placed 10 m away from the STVPL (Figure S1b, Supporting Information). 2.3.2. Measurements as a Function of Distance. Site C. The parameters measured at this site were the vertical dc e-field, net ambient aerosol particle charge concentration, aerosol particle number concentration, and net ambient ion concentration. In conducting these measurements, one e-field meter (Ef1) was placed at a distance of 50 m in the upwind direction (U50) to the HTVPLs, while the AE, P-Trak, a second e-field meter (Ef2), and meteorological station were placed 50 m downwind (D50) of the lines. Two additional field meters (Ef3 and Ef4) were placed downwind of the lines at 100 m (D100) and 150 m (D150), respectively (Figure S1c, Supporting Information). At site C, the AIC was used for the spot measurement of net ambient ion concentration. With all instruments set to sample and log data at a time interval of 1 s, the e-field meters (Ef1, Ef2, Ef3, and Ef4) simultaneously measured dc e-field at four different locations (U50, D50, D100, and D150). But since only one P-Trak and AE were used in the study, both instruments had to be moved from one sampling distance to the other during the course of sampling. As a result, the effect of possible fluctuation in source concentration with time had to be taken into consideration and minimized. This was achieved by employing one sampling distance (D50) as a reference point and subsequently sampling alternately from this reference point and the other sampling distances (U50, L00, D100, D200) with the AE and P-Trak. All measured parameters with the exception of wind were monitored directly under the HTVPL (L00) and as a function of distance from the HTVPL. The schematic diagrams of these sampling sites and positions of all the sampling instruments relative to the powerlines are shown in Figures S1a-c in the Supporting Information of this paper. 2.4. Data Analysis. Since the installation of the HTVPL at site C was almost in the form of a letter “L”, it was decided to investigate only the impact of ions generated by length “g to h” of the line on the environment. This was achieved by calculating the angle each sampling distance (U50, D50, D100, and D200) makes with the opposite ends (i.e., point “g” and “h”) of the HTVPL and only this subset of data was used in the analysis. Further, in assessing aerosol particle charge and number concentration as a function of distance, the mean concentration (based on the angles) obtained at each sampling distance was normalized. Normalization was achieved by calculating the ratio of the concentrations obtained at U50, D50, D100, and D200 to the immediate preceding or succeeding reference point (D50) measurement, taken at a time interval of not more than 1 h apart. The data VOL. 44, NO. 1, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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set was analyzed using simple linear regression, correlation, and multivariate (principal component, factor, classification, and regression tree-CART) analysis. The strength of the regression was tested with coefficient of determinations R2, and statistical significance was asserted at the 95% confidence level.
3. Results This study found that the presence of corona ions in the air environment of the electricity transmission powerlines had significant effect on the local dc e-field, ambient particle charge, and ambient ion concentration levels. The overall results obtained from the study also revealed substantial within-site and between-site variations in the mean estimates of the measured electrical parameters. Apart from the days when high concentrations of ions and charged particles were recorded in the air environment of the powerlines, there were also days when the recorded values of some parameters (especially dc e-field and aerosol particle charge concentration) indicated that very little or minimal corona ions were generated by the investigated powerlines. On such days, these parameters had values that were in the range of what was obtained in another study (18), for a normal (away from any known ion-emitting source) outdoor environment. The cause of these low values is not exactly known, but the possibility that transmission voltages might have been lower on such days could not be ruled out. To achieve the aims of this study, therefore, the data set used were those when the magnitude of these parameters were significantly different from those of the background, and this was used as an indication that corona ions were being generated by the powerlines. 3.1. Measurements at a Distance of Less Than 10 m. The predominant ion polarity at site A was positive; this was inspite of the fact that both positive and negative polarities of ions/charged particles were recorded as being present in this air environment. According to the measured electrical parameters, background values suggesting minimal corona ion discharges were recorded on 3 out of 10 sampling days, while predominantly positive polarity of ions were recorded on the remaining 7 days. The overall results obtained at site A gave respective maximum and minimum mean net air ion concentration levels of 4922 and 2893 ions cm-3 and maximum and minimum mean net aerosol particle charge concentration of 1469 and 727 ions cm-3, as well as maximum and minimum magnitude of vertical dc e-field of 396 and 243 V m-1. The earth’s natural dc e-field (average of 70 V m-1), measure in the same locality as the powerlines (but well away from any electrical infrastructure, buildings, or trees) showed diurnal variation on a much slower time scale compared to the magnitude of the vertical dc e-field in the proximity of the corona ion-emitting HVPLs. The mean ambient particle number concentration at this site was on the order of 103 particle cm-3 for all the sampling days. It was also observed that in line with the predominant (positive) polarity of ions generated by the powerlines and invariably the polarity of the excess ions/charged particles in this air environment, the predominant polarity of the dc e-field was also of the positive polarity (i.e., the field was directed downward). At site B, background values suggesting minimal corona discharges were observed on 2 days, while predominantly negative polarity of ions was recorded on 1 day. Mean net aerosol particle charge concentration levels of -987 ( 1111 ions cm-3, vertical dc e-field of 47 ( 28 V m-1, and particle number concentrations on the order of 103 particle cm-3 were recorded at site B. The SD is greater than the mean, itself testifying to the variability of the e-field. The mean dc e-field at site B was less than the earth’s average natural dc 528
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TABLE 1. Mean Net Aerosol Particle Charge Concentration, Net Particle Number Concentration and DC E-Field, as a Function of Distance from the HTVPL at Site C instrument positiona (m)
mean net particle charge (ions cm-3)
mean dc e-field (V m-1)
mean particle number (particles cm-3)
U50 L00 D50 D100 D200
252 ( 174 299 ( 194 518 ( 317 332 ( 283 -94 ( 320
196 ( 130 458 ( 150 628 ( 194 429 ( 186 413 ( 179
1.3 ( 0.1 × 103 3.2 ( 0.2 × 103 1.8 ( 0.07 × 103 0.7 ( 0.1 × 103 1.4 ( 0.3 × 103
a Directly under the powerline (L00), 50 m upwind (U50), 50 m downwind (D50), 100 m downwind (D100), and 200 m downwind (D200).
e-field, which is an indication that the polarity of the e-field at the site was predominantly negative. 3.2. Measurements as a Function of Distance. The predominant polarity of ions/charged particles in the air environment of the transmission powerline at site C was positive. In Table 1 is presented a summary of the results obtained at this site, showing the recorded variation in local vertical dc e-field, mean net particle charge, and mean net particle number concentration levels. As expected, higher concentrations of ions/charged particles and e-field perturbations were recorded in the downwind direction than the upwind direction of the HTVPL. However, with increase in distance from the lines, statistically significant but gradual decrease was also recorded in the mean values of these parameters. Particle number concentrations were on the order of 103 particle cm-3 at all the distances sampled. The results obtained from normalizing net aerosol particle charge and particle number concentration as a function of distance from the HTVPL indicted that while net particle charge concentration decreased with distance from the powerlines, no statistically significant trend could be associated with particle number concentration (Figure 1a,b). In these figures, the negative distance values refer to upwind directions, positive refer to downwind directions, while zero is directly under the powerline. The error bars represent the standard deviation (σ). 3.3. Effect of Meteorology. The meteorological conditions during the entire sampling were temperature range of 7.5-40.0 °C, atmospheric pressure range of 850.0-1027.9 hPa, solar radiation of 11.9-1419.6 W m-2, relative humidity range of 30.0-61.1%, wind speed of 0-5.5 m s-1, and wind direction of 0-360°. Statistical (linear regression and multivariate) analysis revealed that meteorology had very strong effects on the instantaneous values of all the measured electrical parameters. The CART analysis showed that for the three powerline sites investigated, temperature (solar radiation), humidity, wind speed, and wind direction were dominant meteorological variables for describing the instantaneous value of the measured electrical parameters. 3.3.1. Effect of Wind Speed. Measurement at Distances of Less Than 10 m. Regression analysis performed on the data collected at sites A and B showed no statistically significant effect of wind speed on vertical dc e-field, aerosol particle number, and net particle charge concentration. However, the net ambient ion concentration increased with wind speed and showed a maximum at a value of between 3 and 5 m s-1. Figure 2 is a graphic presentation of this observed trend at one of the powerline sites. Measurements as a Function of Distance. At site C, wind speed had no statistically significant effect on the mean particle number concentration, while mean net particle charge concentration gradually increased with wind speed at four (80%) out of the five different sampling distances
FIGURE 1. (a) Normalized mean aerosol particle number concentration and (b) normalized mean aerosol particle charge concentration.
FIGURE 4. Mean (upwind and downwind) particle charge concentration as a function of wind speed. FIGURE 2. Mean net particle charge, ion concentration, and dc e-field, measured at site A.
FIGURE 3. Mean (upwind and downwind) particle number concentration as a function of wind speed.
FIGURE 5. Mean dc e-field (directly under the line) as a function of wind speed.
(Figures 3 and 4). The e-field meters placed directly under (L00) and downwind of the lines (D50, D100, and D150) also recorded the significant (increasing) effect of wind speed on the local dc e-field. Dc e-field increased up to an optimum wind speed value of 3-4 m s-1 at L00 (Figure 5) and between 4 and 4.5 m s-1 at all other downwind distances (Figure 6). After these wind speed values, the observed effect started to decrease. Statistically, strong associations (R2 > 0.72, p > 0.5) were found to exist between dc e-field and wind speed at all the sampling distances. A supplementary t test of differences between means also confirmed these results. 3.4. Effect of Wind Direction. The overall wind direction during sampling was from 0° to 360°. But at site C, by taking into consideration the angle each sampling distance makes with length “g to h” of the HTVPL, the wind direction range
at site C reduced (5.4°-160°). The results obtained consistently showed that for all the owerline sites, the instantaneous values of the electrical parameters were mostly influenced by winds blowing from the direction of the powerlines. Higher concentrations of ions/charged particles and e-field perturbations were associated with winds blowing from the direction of the lines compared to winds from any other direction. In addition, within a given wind direction, wide variations were also recorded in the mean values of the electrical parameters. These observed variations were deemed responsible for the huge magnitude of standard deviation (σ) recorded in the study (Figure S2, Supporting Information) and may be a result of variable wind turbulence at different heights above the ground. The observation that the net particle charge concentration in Figure 4 was not maximal VOL. 44, NO. 1, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 6. Mean dc e-field (upwind and downwind) as a function of wind speed. at any distance from the powerline at 3-5 m/s may have another explanation. Although high concentrations of ions/charged particles and e-field perturbations were recorded from certain wind directions, the study found that no statistically significant trend could be associated with winds blowing from the powerline direction. A likely explanation for this insignificant trend is the possible existence of more than one corona ion emitting source (i.e., multiple ion sources) along the entire length of the powerlines. 3.5. Relationships between Measured Parameters. Investigations of possible links/associations between ambient ions, aerosol particle charge, particle number, and dc e-field were carried out in two stages (i) by comparing their realtime series variation pattern and (ii) statistically, using Pearson correlations. Comparison of the instantaneous value of aerosol particle charge and particle number when both parameters were simultaneously measured in the environment of the powerlines showed that their time series variation pattern were different. This difference in variation pattern was supported by the extremely low statistical (R2) correlations of between 0.2% and 1.0% found to exist between the instantaneous values of the two parameters. A typical plot of this time variation pattern is presented in Figure S3 (Supporting Information). Similar analysis performed on aerosol particle charge and the local vertical dc e-field also showed their time series patterns to be different. For measurements conducted less than 10 m away from the powerlines, R2 statistical correlations of between 3.4% and 9% were obtained. When measurements were conducted as a function of distance from the powerlines, R2 correlations of 22%, 23%, 25%, and 48% were obtained at distances of U50, L00, D50, and D100, respectively. These correlations, however, improved when averaged over time, as maximum values of 34%, 53%, 67%, and 57% were obtained for a time average of 1.5 min, after which the correlation level started to decrease. Although this study recorded a 3-4-fold difference between the mean values of ambient aerosol particle charge and ion concentration, the instantaneous values of these two parameters were found to be between 42% and 79% correlated (p < 0.05).
4. Discussion The novelty of this study lies in the simultaneous monitoring of a number of parameters characterizing the electrical environment around corona ion-emitting HTVPLs and STVPLs. Being the first of its kind to be conducted in the proximity of real-world energized powerlines, the study has 530
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the potential to serve as a basis for other future and more comprehensive studies that will extend the scope of work presented in this paper. In terms of the results, the study recorded both positive and negative polarities of ions in the air environment of the investigated powerlines, which is an indication that both polarities of ions were generated by these lines during the corona discharge process. This result agrees with the outcome of some other studies which have also reported the presence of positive and negative polarities of ions at various powerline sites (7, 11). However, the reason for dominance/bias toward one polarity of charge versus the other is yet to be fully understood. With respect to the possible effects of meteorology, although higher concentrations of net ambient ions/charged particles and e-field perturbations were recorded in the downwind than the upwind direction of these lines, the mean values of these parameters also gradually decreased with increase in distance downwind of the line. Wind speed was also recorded to have a significant (increasing) effect on the instantaneous values of all the measured electrical parameters (i.e., ambient ions, aerosol charged particle, and e-field perturbations). But since the optimum wind speed value at which this effect is no longer observable varied between parameters and from one powerline site to the other, this suggests the presence of a high degree of wind instability relative to the dispersion and measurement times. Despite the wind dispersal effects, aerosol particle number concentrations still remained the same (103) at all the sites and irrespective of the sampling distance from the powerlines. Similar particle number concentration levels to these were obtained in a different study, in the proximity of a nearthe-ground high-voltage electrical infrastructure (18), and these values are well within the range for a typical outdoor air environment (19). A close investigation of the output of the sampling instruments used consistently revealed large fluctuations (or variation) in the instantaneous value of all the electrical parameters measured. The fluctuations (usually in the form of nonperiodic extremely high and low, negative and positive polarities) of ions/charged particles and e-field perturbations were considered to be responsible for the large standard deviations recorded in this study. Similar fluctuations to these were also reported by other studies. But according to a study which investigated 42 different HVPL sites (20), these fluctuations appeared to be characteristic of the electrical environment around corona ion-emitting powerlines and hence were found to be absent when ambient ions and e-field measurements were conducted in other outdoor environments, situated well away from HVPLs sites. Consequently, it is being hypothesized that the fluctuations may perhaps be suggestive of the possibility that the release of corona ions by ac lines may not necessarily be as a continuous flow. According to Table 1, at site C the predominant polarity of ions/charged particles in the ambient environment was positive. At a downwind distance of 200 m, however, the ground-level net particle charge concentration was of the negative polarity (-94 ( 320 ions cm-3) and only slightly more positive than the value (-486 ( 34 ions cm-3) obtained by another study in a typical urban outdoor air environment (18). But at this same sampling position, the recorded vertical dc e-field (413 ( 179 V m-1) was of the positive polarity and about six times higher than the earth’s natural dc e-field of 70 V m-1 (obtained in the same locality as the investigated powerlines). This observed difference in polarity and the fact that while ground-level particle charge concentration was almost of the background value the vertical dc e-field remained relatively high were attributed to a number of factors, such as the prevailing meteorology (mostly wind dispersal and turbulence) as well as the principles of operation of the sampling instruments. For instance, as a plume of
corona ions/charged particles moves within the atmospheric system, it undergoes vertical dispersion, which causes the dilution and invariably the scattering of these ions/charged particle within the system. An e-field meter set to measure the effect of these ions/charged particles within this environment will give an integrated net e-field reading that is associated with the net concentration of ions contained in the large volume of air above the sampling point. But, since the measurement range of the aerosol electrometer is limited to only the air sampled via a small inlet at the front of the instrument, the ions/charged particles concentration above the ground level do not influence the electrometer’s readings. This explains the reason why (i) statistically low (R2) correlations were obtained in this study between the ground level ambient particle charge concentration and vertical dc e-field, despite the fact that both parameters were strongly influenced by the presence of corona ions, and (ii) e-field measurements are not necessarily a true representation of the ground-level ambient ion/particle charge concentration levels. In addition, these results also suggest that in terms of particle charge concentration at site C, the ground-level effect of corona ions generated by the HTVPLs were localized and limited to a distance of about 200 m from the line, though it must be emphasized that this is not implying that all corona ion effects are limited to distances of less than 200 m from the emitting lines, especially since some studies have found space charge effects 500 m away from a 275 kV line (11). But rather that, the real-world electrical effects of corona ions generated by energized voltage powerlines are subject to a number of factors, such as their (ions/charged particles) ambient concentration levels, distance from the corona ion source, the prevailing meteorology of wind turbulence and dispersal. The study also found that no statistically significant correlations exist between aerosol particle number and aerosol particle charge concentration. This showed that there is no substantial link between the two parameters in the proximity of powerlines and their source contribution to this ambient environment was potentially different. Similar low correlations between aerosol particle number and aerosol particle charge concentration were also obtained in a separate study that characterized the electrical environment of a strong corona ion-emitting source (18).
5. Conclusions In summary, this paper gives an assessment of the effect of corona ions generated by energized high/subtransmission voltage powerlines on the local vertical dc e-field, ambient ion concentration, aerosol particle number, and particle charge concentration levels, under real-world conditions. However, there is need for more studies to follow up on the findings presented in this study. The follow-up studies should be conducted under different diurnal, seasonal, and more extreme weather conditions (as it is possible that the results obtained in this study may not have reflected the strong influence of humidity due to the desired meteorological condition for sampling). Among other things, the possible effects of real-world high-voltage powerline characteristics (i.e., operating voltages and peak current), conductor surface contamination, etc. also need further investigation.
Acknowledgments This work was conducted under the Australian Research Council (LP0562205) Linkage grant. We thank our industry
partner (Australian Strategic Technology Programme) for their invaluable assistance.
Supporting Information Available Additional information as outlined in the text. This material is available free of charge via the Internet at http:// pubs.acs.org.
Literature Cited (1) Phillips, A. J.; Childs, D. J.; Schneider, H. M. Aging of nonceramic insulators due to corona from water drops. Power Delivery, IEEE Trans. 1999, 14 (3), 1081–1089. (2) Maruvada, S. P. Corona Performance of High-Voltage Transmission Lines; Research Studies Press Ltd: Baldock, England, 2000. (3) Nie, Y.; Yin, X.; Liu, C.; Wen, Y.; Mao, M.; Tian, Z. In Research into the Corona Current Characteristics of Polluted Insulators. Proceedings of 2001 International Symposium on Electrical Insulating Materials, 2001 (ISEIM 2001). IEEJ: Tokyo, 2001; pp 47-50. (4) MacAlpine, J. M. K.; Zhang, C. H. The effect of humidity on the charge/phase-angle patterns of AC corona pulses in air. IEEE Trans. Dielectr. Electr. Insul. 2003, 10 (3), 506–513. (5) Abdel-Salam, M.; Mufti, A. Analysis of corona losses on monopolar dc transmission lines. Electric Power Syst. Res. 1998, 44 (2), 145–154. (6) Abdel-Salam, M.; Abdallah, H. Induced fields, charges and currents on a human underneath power transmission lines. Proceedings of the 15th Annual International Conference of the IEEE Engineering in Medicine and Biology Society; IEEE: Piscataway, NJ, 1993; p 14261427. (7) Fews, A. P.; Henshaw, D. L.; Wilding, R. J.; Keitch, P. A. Corona ions from powerlines and increased exposure to pollutant aerosols. Int. J. Radiat. Biol. 1999, 75 (12), 1523–1531. (8) Hoppel, W. A.; Frick, G. M. Ion-aerosol attachment coefficients and the steady-state charge distribution on aerosols in a bipolar ion environment. Aerosol Sci. Technol. 1986, 5, 1–21. (9) Nagato, K.; Ogawa, T. Evolution of tropospheric ions observed by an ion mobility spectrometer with a drift tube. J. Geophys. Res. 1998, 103 (D12), 13917–13925. (10) Viggiano, A. A. In situ mass spectrometry and ion chemistry in the stratosphere and troposphere. Mass Spectrom. Rev. 1993, 12, 115–137. (11) Wilding, R. J.; Fews, A. P.; Henshaw, D. L.; Keitch, P. A. Increase exposure to pollutant aerosol in electrically charged atmospheres that exist around high voltage powerlines. J. Aerosol Sci. 2000, 31 (1), S1023–S1024. (12) Guler, G.; Seyhan, N. The effects of electric fields on biological systems. Engineering in Medicine and Biology Society, 2001. Proceedings of the 23rd Annual International Conference of the IEEE; IEEE: Piscataway, NJ, 2001; Vol. 2, pp 1023-1025. (13) Krueger, A. P.; Reed, E. J. Biological impact of small air ions. Science 1976, 193, 1209–1213. (14) J-Fatokun, F. O.; Morawska, L.; Jayaratne, E. R. Application of aerosol electrometer for ambient particle charge measurements. Atmos. Environ. 2008, 42, 8827-8830. (15) Model 8525 P-TRAK Ultrafine Particle Counter Operation and Service Manual; TSI: Shoreview, MN, 2004; Vol. Revision H. (16) Aerosol Electrometer (AE) Model 3068A Instruction Manual; TSI: Shoreview, MN, 2003. (17) Bennett, A. J.; Harrison, G. R. Atmospheric electricity in different weather conditions. Weather 2007, 62 (10), 277–283. (18) J-Fatokun, F. O.; Jayaratne, E. R.; Morawska, L.; Rachman, R.; Birtwhistle, D.; Mengersen, K. Characterization of the atmospheric electrical environment near a corona ion emitting source. Atmos. Environ. 2008, 42 (7), 1607–1616. (19) Morawska, L.; Thomas, S.; Bofinger, N.; Wainwright, D.; Neale, D. Comprehensive characterization of aerosols in a subtropical urban atmosphere: Particle size distribution and correlation with gaseous pollutants. Atmos. Environ. 1998, 32 (14-15), p 2467–2478. (20) Jayaratne, E. R.; J-Fatokun, F. O.; Morawska, L. Air ion concentrations under overhead high-voltage transmission lines. Atmos. Environ. 2008, 42 (8), 1846–1856.
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