Influence of filtration on I/O particle concentration ratios at urban office buildings

Epidemiological research has consistently shown an association between fine and ultrafine particle concentrations, and increases in both respiratory and cardiovascular morbidity and mortality. These particles, often found in vehicle emissions outside buildings, can penetrate inside via their envelopes and mechanically ventilated systems. Indoor activities such as printing, cooking and cleaning, as well as the movement of building occupants are also an additional source of these particles. In this context, the filtration systems of mechanically ventilated buildings can reduce indoor particle concentrations. Several studies have quantified the efficiency of dry-media and electrostatic filters, but they mainly focused on the particle size range > 300 nm. Some others studied ultrafine particles but their investigations were conducted in laboratories. At this point, there is still only limited information on in situ filter efficiency and an incomplete understanding of filtration influence on I/O ratios of particle concentrations. To help address these gaps in knowledge and provide new information for the selection of appropriate filter types in office building HVAC systems, we aimed to: (1) measure particle concentrations at up and down stream flows of filter devices, as well as outdoor and indoor office buildings; (2) quantify efficiency of different filter types at different buildings; and (3) assess the impact of these filters on I/O ratios at different indoor and outdoor source operation scenarios

Characterization of particle number concentrations and PM2.5 in a school: influence of outdoor air pollution on indoor air

Background, Aim and Scope The impact of air pollution on school children’s health is currently one of the key foci of international and national agencies. Of particular concern are ultrafine particles which are emitted in large quantities, contain large concentrations of toxins and are deposited deeply in the respiratory tract. Materials and methods In this study, an intensive sampling campaign of indoor and outdoor airborne particulate matter was carried out in a primary school in February 2006 to investigate indoor and outdoor particle number (PN) and mass concentrations (PM2.5), and particle size distribution, and to evaluate the influence of outdoor air pollution on the indoor air. Results For outdoor PN and PM2.5, early morning and late afternoon peaks were observed on weekdays, which are consistent with traffic rush hours, indicating the predominant effect of vehicular emissions. However, the temporal variations of outdoor PM2.5 and PN concentrations occasionally showed extremely high peaks, mainly due to human activities such as cigarette smoking and the operation of mower near the sampling site. The indoor PM2.5 level was mainly affected by the outdoor PM2.5 (r = 0.68, p<0.01), whereas the indoor PN concentration had some association with outdoor PN values (r = 0.66, p<0.01) even though the indoor PN concentration was occasionally influenced by indoor sources, such as cooking, cleaning and floor polishing activities. Correlation analysis indicated that the outdoor PM2.5 was inversely correlated with the indoor to outdoor PM2.5 ratio (I/O ratio) (r = -0.49, p<0.01), while the indoor PN had a weak correlation with the I/O ratio for PN (r = 0.34, p<0.01). Discussion and Conclusions The results showed that occupancy did not cause any major changes to the modal structure of particle number and size distribution, even though the I/O ratio was different for different size classes. The I/O curves had a maximum value for particles with diameters of 100 – 400 nm under both occupied and unoccupied scenarios, whereas no significant difference in I/O ratio for PM2.5 was observed between occupied and unoccupied conditions. Inspection of the size-resolved I/O ratios in the preschool centre and the classroom suggested that the I/O ratio in the preschool centre was the highest for accumulation mode particles at 600 nm after school hours, whereas the average I/O ratios of both nucleation mode and accumulation mode particles in the classroom were much lower than those of Aitken mode particles. Recommendations and Perspectives The findings obtained in this study are useful for epidemiological studies to estimate the total personal exposure of children, and to develop appropriate control strategies for minimizing the adverse health effects on school children

Exposure to particles from laser printers operating within office workplaces

While recent research has provided valuable information as to the composition of laser printer particles, their formation mechanisms, and explained why some printers are emitters whilst others are low emitters, fundamental questions relating to the potential exposure of office workers remained unanswered. In particular, (i) what impact does the operation of laser printers have on the background particle number concentration (PNC) of an office environment over the duration of a typical working day?; (ii) what is the airborne particle exposure to office workers in the vicinity of laser printers; (iii) what influence does the office ventilation have upon the transport and concentration of particles?; (iv) is there a need to control the generation of, and/or transport of particles arising from the operation of laser printers within an office environment?; (v) what instrumentation and methodology is relevant for characterising such particles within an office location? We present experimental evidence on printer temporal and spatial PNC during the operation of 107 laser printers within open plan offices of five buildings. We show for the first time that the eight-hour time-weighted average printer particle exposure is significantly less than the eight-hour time-weighted local background particle exposure, but that peak printer particle exposure can be greater than two orders of magnitude higher than local background particle exposure. The particle size range is predominantly ultrafine (< 100nm diameter). In addition we have established that office workers are constantly exposed to non-printer derived particle concentrations, with up to an order of magnitude difference in such exposure amongst offices, and propose that such exposure be controlled along with exposure to printer derived particles. We also propose, for the first time, that peak particle reference values be calculated for each office area analogous to the criteria used in Australia and elsewhere for evaluating exposure excursion above occupational hazardous chemical exposure standards. A universal peak particle reference value of 2.0 x 104 particles cm-3 has been proposed

First observations of new particle formation in Beijing using a neutral cluster and air ion spectrometer (NAIS)

The ILAQH neutral cluster and air ion spectrometer (NAIS) was operated for a continuous period of three months from November 2015 to January 2016 as part of a major air quality monitoring campaign coordinated by the Chinese Research Academy of Environmental Sciences in Beijing. The NAIS provides neutral and charged particle and cluster concentrations in real time in the size range 0.5 to 42 nm. Molecular clusters of precursor gases transform into particles at a size of about 1.6 nm - a phenomenon that is known as nucleation or new particle formation (NPF). NPF requires a sufficiently high level of gaseous supersaturation in the air – a condition that is mitigated by the presence of high concentration of particles in the atmosphere. November and December 2015 was characterised by several severe pollution episodes in Beijing, yielding mean daily PM2.5 levels of 120 and 154 µg m-3, respectively. The average daily PM2.5 level exceeded 100 µg m 3 on most days. However, the pollution level eased during January 2016 giving a mean daily PM2.5 level of 67 µg m 3. The mean number of NPF events observed per month in November and December was just over 4, and in January it increased to 16. In this paper, we will show that severe pollution events in Beijing occur in a cycle of 5-8 days and generally coincide with winds that bring industrial pollution from the south. Successive severe pollution episodes are separated by 2-5 days of relatively clean air periods coinciding with winds from the less-industrialized north. NPF events almost always occurred during these clean air periods

Microbial contents of vacuum cleaner bag dust and emitted bioaerosols and their implications for human exposure indoors

Vacuum cleaners can release large concentrations of particles, both in their exhaust air and from resuspension of settled dust. However, the size, variability, and microbial diversity of these emissions are unknown, despite evidence to suggest they may contribute to allergic responses and infection transmission indoors. This study aimed to evaluate bioaerosol emission from various vacuum cleaners. We sampled the air in an experimental flow tunnel where vacuum cleaners were run, and their airborne emissions were sampled with closed-face cassettes. Dust samples were also collected from the dust bag. Total bacteria, total archaea, Penicillium/Aspergillus, and total Clostridium cluster 1 were quantified with specific quantitative PCR protocols, and emission rates were calculated. Clostridium botulinum and antibiotic resistance genes were detected in each sample using endpoint PCR. Bacterial diversity was also analyzed using denaturing gradient gel electrophoresis (DGGE), image analysis, and band sequencing. We demonstrated that emission of bacteria and molds (Penicillium/Aspergillus) can reach values as high as 1E5 cell equivalents/min and that those emissions are not related to each other. The bag dust bacterial and mold content was also consistent across the vacuums we assessed, reaching up to 1E7 bacterial or mold cell equivalents/g. Antibiotic resistance genes were detected in several samples. No archaea or C. botulinum was detected in any air samples. Diversity analyses showed that most bacteria are from human sources, in keeping with other recent results. These results highlight the potential capability of vacuum cleaners to disseminate appreciable quantities of molds and human-associated bacteria indoors and their role as a source of exposure to bioaerosols

Airborne Particles in Indoor Residential Environment: Source Contribution, Characteristics, Concentration, and Time Variability

The understanding of human exposure to indoor particles of all sizes is important to enable exposure control and reduction, but especially for smaller particles since the smaller particles have a higher probability of penetration into the deeper parts of the respiratory tract and also contain higher levels of trace elements and toxins. Due to the limited understanding of the relationship between particle size and the health effects they cause, as well as instrument limitations, the available information on submicrometer (d < 1.0 µm) particles indoors, both in terms of mass and number concentrations, is still relatively limited. This PhD project was conducted as part of the South-East Queensland Air Quality program and Queensland Housing Study aimed at providing a better understanding of ambient particle concentrations within the indoor environment with a focus on exposure assessment and control. This PhD project was designed to investigate comprehensively the sources and sinks of indoor aerosol particles and the relationship between indoor and outdoor aerosol particles, particle and gaseous pollutant, as well as the association between indoor air pollutants and house characteristics by using, analysing and interpreting existing experimental data which were collected before this project commenced, as well as data from additional experiments which were designed and conducted for the purpose of this project. The focus of this research was on submicrometer particles with a diameter between 0.007 - 0.808 µm. The main outcome of this project may be summarised as following: * A comprehensive review of particle concentration levels and size distributions characteristics in the residential and non-industrial workplace environments was conducted. This review included only those studies in which more general trends were investigated, or could be concluded based on information provided in the papers. This review included four parts: 1) outdoor particles and their effect on indoor environments; 2) the relationship between indoor and outdoor concentration levels in the absence of indoor sources for naturally ventilated buildings; 3) indoor sources of particles: contribution to indoor concentration levels and the effect on I/O ratios for naturally ventilated buildings; and 4) indoor/outdoor relationship in mechanically ventilated buildings. * The relationship between indoor and outdoor airborne particles was investigated for sixteen residential houses in Brisbane, Australia, in the absence of operating indoor sources. Comparison of the ratios of indoor to outdoor particle concentrations revealed that while temporary values of the ratio vary in a broad range from 0.2 to 2.5 for both lower and higher ventilation conditions, average values of the ratios were very close to one regardless of ventilation conditions and of particle size range. The ratios were in the range from 0.78 to 1.07 for submicrometer particles, from 0.95 to 1.0 for supermicrometer particles and from 1.01 to 1.08 for PM2.5 fraction. Comparison of the time series of indoor to outdoor particle concentrations showed a clear positive relationship existing for many houses under normal ventilation conditions (estimated to be about and above 2 h-1), but not under minimum ventilation conditions (estimated to be about and below 1 h-1). These results suggest that for normal ventilation conditions and in the absence of operating indoor sources, outdoor particle concentrations could be used to predict instantaneous indoor particle concentrations but not for minium ventilation, unless air exchange rate is known, thus allowing for estimation of the "delay constant". * Diurnal variation of indoor submicrometer particle number and particle mass (approximation of PM2.5) concentrations was investigated in fifteen of the houses. The results show that there were clear diurnal variations in both particle number and approximation of PM2.5 concentrations, for all the investigated houses. The pattern of diurnal variations varied from house to house, however, there was always a close relationship between the concentration and human indoor activities. The average number and mass concentrations during indoor activities were (18.2±3.9)×10³ particles cm-³ and (15.5±7.9) µg m-³ respectively, and under non-activity conditions, (12.4±2.7)x10³ particles cm-³ (11.1±2.6) µg m-³, respectively. In general, there was a poor correlation between mass and number concentrations and the correlation coefficients were highly variable from day to day and from house to house. This implies that conclusions cannot be drawn about either one of the number or mass concentration characteristics of indoor particles, based on measurement of the other. The study also showed that it is unlikely that particle concentrations indoors could be represented by measurements conducted at a fixed monitoring station due to the large impact of indoor and local sources. * Emission characteristics of indoor particle sources in fourteen residential houses were quantified. In addition, characterizations of particles resulting from cooking conducted in an identical way in all the houses were measured. All the events of elevated particle concentrations were linked to indoor activities using house occupants diary entries, and catalogued into 21 different types of indoor activities. This enabled quantification of the effect of indoor sources on indoor particle concentrations as well as quantification of emission rates from the sources. For example, the study found that frying, grilling, stove use, toasting, cooking pizza, smoking, candle vaporizing eucalyptus oil and fan heater use, could elevate the indoor submicrometer particle number concentration levels by more than 5 times, while PM2.5 concentrations could be up to 3, 30 and 90 times higher than the background levels during smoking, frying and grilling, respectively. * Indoor particle deposition rates of size classified particles in the size range from 0.015 to 6 µm were quantified. Particle size distribution resulting from cooking, repeated under two different ventilation conditions in 14 houses, as well as changes to particle size distribution as a function of time, were measured using a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), and a DustTrak. Deposition rates were determined by regression fitting of the measured size-resolved particle number and PM2.5 concentration decay curves, and accounting for air exchange rate. The measured deposition rates were shown to be particle size dependent and they varied from house to house. The lowest deposition rates were found for particles in the size range from 0.2 to 0.3 µm for both minimum (air exchange rate: 0.61±0.45 h-1) and normal (air exchange rate: 3.00±1.23 h-1) ventilation conditions. The results of statistical analysis indicated that ventilation condition (measured in terms of air exchange rate) was an important factor affecting deposition rates for particles in the size range from 0.08 to 1.0 µm, but not for particles smaller than 0.08 µm or larger than 1.0 µm. Particle coagulation was assessed to be negligible compared to the two other processes of removal: ventilation and deposition. This study of particle deposition rates, the largest conducted so far in terms of the number of residential houses investigated, demonstrated trends in deposition rates comparable with studies previously reported, usually for significantly smaller samples of houses (often only one). However, the results compare better with studies which, similarly to this study, investigated cooking as a source of particles (particle sources investigated in other studies included general activity, cleaning, artificial particles, etc). * Residential indoor and outdoor 48 h average levels of nitrogen dioxide (NO2), 48h indoor submicrometer particle number concentration and the approximation of PM2.5 concentrations were measured simultaneously for fourteen houses. Statistical analyses of the correlation between indoor and outdoor pollutants (NO2 and particles) and the association between house characteristics and indoor pollutants were conducted. The average indoor and outdoor NO2 levels were 13.8 ± 6.3 ppb and 16.7 ± 4.2 ppb, respectively. The indoor/outdoor NO2 concentration ratio ranged from 0.4 to 2.3, with a median value of 0.82. Despite statistically significant correlations between outdoor and fixed site NO2 monitoring station concentrations (p = 0.014, p = 0.008), there was no significant correlation between either indoor and outdoor NO2 concentrations (p = 0.428), or between indoor and fixed site NO2 monitoring station concentrations (p = 0.252, p = 0.465,). However, there was a significant correlation between indoor NO2 concentration and indoor submicrometer aerosol particle number concentrations (p = 0.001), as well as between indoor PM2.5 and outdoor NO2 (p = 0.004). These results imply that the outdoor or fixed site monitoring concentration alone is a poor predictor of indoor NO2 concentration. * Analysis of variance indicated that there was no significant association between indoor PM2.5 and any of the house characteristics investigated (p > 0.05). However, associations between indoor submicrometer particle number concentration and some house characteristics (stove type, water heater type, number of cars and condition of paintwork) were significant at the 5% level. Associations between indoor NO2 and some house characteristics (house age, stove type, heating system, water heater type and floor type) were also significant (p < 0.05). The results of these analyses thus strongly suggest that the gas stove, gas heating system and gas water heater system are main indoor sources of indoor submicrometer particle and NO2 concentrations in the studied residential houses. The significant contributions of this PhD project to the knowledge of indoor particle included: 1) improving an understanding of indoor particles behaviour in residential houses, especially for submicrometer particle; 2) improving an understanding of indoor particle source and indoor particle sink characteristics, as well as their effects on indoor particle concentration levels in residential houses; 3) improving an understanding of the relationship between indoor and outdoor particles, the relationship between particle mass and particle number, correlation between indoor NO2 and indoor particles, as well as association between indoor particle, NO2 and house characteristics

Particle Deposition Rates in Residential Houses

As part of a large study investigating indoor air in residential houses in Brisbane, Australia, the purpose of this work was to quantify the particle deposition rate of size classified particles in the size range from 0.015 to 6 micrometres. Particle size distribution resulting from cooking, repeated under two different ventilation conditions in 14 houses, as well as changes to particle size distribution and PM2.5 concentration as a function of time, were measured using a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), and a DustTrak. Deposition rates were determined by regression fitting of the measured size-resolved particle number and PM2.5 concentration decay curves, and accounting for air exchange rate. The measured deposition rates were shown to be particle size dependent and they varied from house to house. The lowest deposition rates were found for particles in the size range from 0.2 to 0.3 micrometres for both minimum (air exchange rate: 0.6170.45 h-1) and normal (air exchange rate: 3.0071.23 h-1) ventilation conditions. The results of statistical analysis indicated that ventilation condition (measured in terms of air exchange rate) was an important factor affecting deposition rates for particles in the size range from 0.08 to 1.0 micrometres, but not for particles smaller than 0.08 micrometres or larger than 1.0 micrometres. Particle coagulation was assessed to be negligible compared to the two other processes of removal: ventilation and deposition. This study of particle deposition rates, the largest conducted so far in terms of the number of residential houses investigated, demonstrated trends in deposition rates comparable with studies previously reported, usually for significantly smaller samples of houses (often only one). However, the results compare better with studies which, similarly to this study, investigated cooking as a source of particles (particle sources investigated in other studies included general activity, cleaning, artificial particles, etc)

Effect of outdoor site location on calculated I/O ratios

Motor vehicle emissions have been identified as one of the major contributors of fine and ultrafine particles (UFP) in urban areas. Schools located near major roads could potentially be exposed to high levels of UPFs and school classroom is an important microenvironment where significant exposure to UFPs is likely to occur. Most of the research conducted to date has investigated the relationship between indoor and outdoor particle number concentration (PNC) in schools based on one outdoor location, which may introduce a level of error when calculating the variation of total UPFs, and can result in the underestimation or overestimation of indoor to outdoor (I/O) ratio values

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

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