Indoor-generated Particles Research Articles

Air pollution and respiratory health in patients with COPD: should we focus on indoor or outdoor sources?

IntroductionWhile associations between ambient air pollution and respiratory health in chronic obstructive pulmonary disease (COPD) patients are well studied, little is known about individuals’ personal exposure to pollution and associated...

Performance of a heat recovery ventilation system for controlling human exposure to airborne particles in a residential building

Heat recovery ventilation (HRV) system is emerging as a sustainable technology to reduce human exposure to air pollutants in residential buildings. However, there is a lack of information on the HRV system performance for controlling both indoor-generated and outdoor-generated particles in a residential building. To fill this knowledge gap, we conducted field monitoring of indoor airborne particles with two representative HRV system operating modes (ventilation and circulation modes) in a full-scale residential testbed. The results reveal that the filter efficiency, airflow rate, and filter bypass factor of the HRV system play important roles in indoor particle concentrations. The indoor/outdoor concentration ratio is reduced by 72%–92% when operating the HRV system. For both circulation and ventilation modes, the bypass factor is crucial for the particle removal performance of the HRV system. A 20% filter bypass factor leads to up to a 50% increase in indoor exposure to outdoor-originated and indoor-generated PM2.5 compared to the no-bypass scenario. Although circulation mode performed better than ventilation mode, both operating modes with a minimal bypass factor can effectively remove particles generated from indoor emission sources (e.g., incense stick burning and bacon pan frying). The study results suggest that HRV system can reduce human exposure to indoor-generated particles by 56%–90% and particle control performance hinges upon minimizing HRV filter bypass.

Indoor PM2.5 from occupied residences in Sweden caused higher inflammation in mice compared to outdoor PM2.5.

We spend most of our time indoors; however, little is known about the effects of exposure to aerosol particles indoors. We aimed to determine differences in relative toxicity and physicochemical properties of PM2.5 collected simultaneously indoors (PM2.5 INDOOR ) and outdoors (PM2.5 OUTDOOR ) in 15 occupied homes in southern Sweden. Collected particles were extracted from filters, pooled (indoor and outdoor separately), and characterized for chemical composition and endotoxins before being tested for toxicity in mice via intratracheal instillation. Various endpoints including lung inflammation, genotoxicity, and acute-phase response in lung and liver were assessed 1, 3, and 28 days post-exposure. Chemical composition of particles used in toxicological assessment was compared to particles analyzed without extraction. Time-resolved particle mass and number concentrations were monitored. PM2.5 INDOOR showed higher relative concentrations (μg mg-1 ) of metals, PAHs, and endotoxins compared to PM2.5 OUTDOOR . These differences may be linked to PM2.5 INDOOR causing significantly higher lung inflammation and lung acute-phase response 1day post-exposure compared to PM2.5 OUTDOOR and vehicle controls, respectively. None of the tested materials caused genotoxicity. PM2.5 INDOOR displayed higher relative toxicity than PM2.5 OUTDOOR under the studied conditions, that is, wintertime with reduced air exchange rates, high influence of indoor sources, and relatively low outdoor concentrations of PM. Reducing PM2.5 INDOOR exposure requires reduction of both infiltration from outdoors and indoor-generated particles.

Indoor contribution to PM2 .5 exposure using all PurpleAir sites in Washington, Oregon, and California.

Low-cost monitors have made it possible for the first time to measure indoor PM2.5 concentrations over extended periods of time (months to years). Coupled with concurrent outdoor measurements, these indoor measurements can be divided into particles entering the building from outdoors and particles generated from indoor activities. Indoor-generated particles are not normally considered in epidemiological studies, but they can have health effects (e.g., passive smoking and high-temperature cooking). We employed The Random Component Superposition (RCS) regression model to estimate infiltration factors for up to 790 000 matched indoor and outdoor sites. The median infiltration factors for subgroups in the 3-state region ranged between 0.22 and 0.24, with an interquartile range (IQR) of 0.13-0.40. These infiltration factors allowed calculation of both the indoor-generated and outdoor-infiltrated PM2.5 . Indoor-generated particles contributed, on average, 46%-52% of total indoor PM2.5 concentrations. However, the site-specific fractional contribution of these indoor sources to total indoor PM2.5 ranged from near-zero to nearly 100%. The influence of indoor-generated particles on potential exposures varied widely relative to outdoor concentrations. The greatest influence of indoor-generated particles occurred at low-to-moderate daily mean outdoor PM2.5 levels around 6μg/m3 and was negligible at outdoor concentrations >20 μg/m3 . Epidemiological studies incorporating only estimated exposures due to the particles of ambient origin may benefit from the newly available knowledge of long-term indoor-generated particle concentrations.

Residential building ventilation in situations with outdoor PM2.5 pollution

Affordable ventilation of residential buildings in situations with outdoor PM2.5 pollution is a challenge. This investigation used the validated EnergyPlus software program to model ventilation performance in a newly constructed residential apartment in five different climate zones in China. The evaluated ventilation modes were natural ventilation, balanced mechanical ventilation, and hybrid ventilation, together with indoor particle filtration. Both indoor-generated particles due to cooking and ventilation-drawn particles from the outdoor environment were considered. Different heat recovery modes for mechanical ventilation were also compared. The evaluated parameters included indoor CO2 (carbon dioxide), PM2.5 (fine particulate matter), formaldehyde, and TVOC (total volatile organic compound) concentrations, energy consumption, and operating costs. The natural ventilation mode was found to be the cheapest, but it may provide an insufficient ventilation rate for 27%–79% of the occupied time. Mechanical ventilation can ensure good indoor air quality continuously, but the associated utility cost may be more than twice that for natural ventilation. Indoor particulate filtration should be utilized in situations with severe outdoor PM2.5 pollution. Heat recovery is not recommended in residential buildings due to the high initial investment cost at present. The least energy-consuming ventilation mode for residential buildings with maximum potential to use natural ventilation is recommended.

Commuter exposure to particulate matters in four common transportation modes in Nanjing

Particulate matter (PM) is one of the major air pollutants in China. Traffic-related microenvironments are the typical scenarios exposed to high PM concentrations. This paper investigates the personal exposure to PM during commuting in Nanjing in four transportation modes, i.e. subway, bicycle, bus and walking. The measurements were conducted in a heavy-traffic street during rush hours in summer and winter. The result reveals significant PM concentration differences between various commuting modes. Passengers in subway cabin are exposed to lowest PM1 (38.3 μg/m3) and PM2.5 (54.4 μg/m3) concentrations, while passengers in subway station are exposed to highest PM2.5 (90.5 μg/m3). Pedestrians are exposed to highest PM1 (59.5 μg/m3). Both outdoor and indoor-generated particles contribute a lot to the particles in subway station and 63.4% of the PM2.5 generated in subway station are between 1 μm and 2.5 μm in size. Most particles in subway cabin are from subway station and most particles in bus cabin come from the outdoor air, while indoor sources contribute little. Spatial particle concentration variations were observed in subway station. The particle concentration at a deeper level is usually higher than the concentration at a shallower level. Substantial particles within 1–2.5 μm in size were observed at the platform and the portion within 1–2.5 μm decreased at shallower levels. The PM inhalation during subway trip is lowest while the inhalations during walking and cycling are more than 5 times higher. During a short distance subway trip, the exposure in subway station contributes most of the total particle inhalation during the entire subway trip.

Measured performance of filtration and ventilation systems for fine and ultrafine particles and ozone in an unoccupied modern California house.

This study evaluated nine ventilation and filtration systems in an unoccupied 2006 house located 250m downwind of the I-80 freeway in Sacramento, California. Systems were evaluated for reducing indoor concentrations of outdoor particles in summer and fall/winter, ozone in summer, and particles from stir-fry cooking. Air exchange rate was measured continuously. Energy use was estimated for year-round operation in California. Exhaust ventilation without enhanced filtration provided indoor PM2.5 that was 70% lower than outdoors. Supply ventilation with MERV13 filtration provided slightly less protection, whereas supply MERV16 filtration reduced PM2.5 by 97-98% relative to outdoors. Supply filtration systems used little energy but provided no benefits for indoor-generated particles. Systems with MERV13-16 filter in the recirculating heating and cooling unit (FAU) operating continuously or 20min/h reduced PM2.5 by 93-98%. Across all systems, removal percentages were higher for ultrafine particles and lower for black carbon, relative to PM2.5 . Indoor ozone was 3-4% of outdoors for all systems except an electronic air cleaner that produced ozone. Filtration via the FAU or portable filtration units lowered PM2.5 by 25-75% when operated over the hour following cooking. The energy for year-round operation of FAU filtration with an efficient blower motor was estimated at 600 kWh/year.

Concentrations and Sources of Airborne Particles in a Neonatal Intensive Care Unit.

Premature infants in neonatal intensive care units (NICUs) have underdeveloped immune systems, making them susceptible to adverse health consequences from air pollutant exposure. Little is known about the sources of indoor airborne particles that contribute to the exposure of premature infants in the NICU environment. In this study, we monitored the spatial and temporal variations of airborne particulate matter concentrations along with other indoor environmental parameters and human occupancy. The experiments were conducted over one year in a private-style NICU. The NICU was served by a central heating, ventilation and air-conditioning (HVAC) system equipped with an economizer and a high-efficiency particle filtration system. The following parameters were measured continuously during weekdays with 1-min resolution: particles larger than 0.3 μm resolved into 6 size groups, CO2 level, dry-bulb temperature and relative humidity, and presence or absence of occupants. Altogether, over sixteen periods of a few weeks each, measurements were conducted in rooms occupied with premature infants. In parallel, a second monitoring station was operated in a nearby hallway or at the local nurses’ station. The monitoring data suggest a strong link between indoor particle concentrations and human occupancy. Detected particle peaks from occupancy were clearly discernible among larger particles and imperceptible for submicron (0.3–1 μm) particles. The mean indoor particle mass concentrations averaged across the size range 0.3–10 μm during occupied periods was 1.9 μg/m3, approximately 2.5 times the concentration during unoccupied periods (0.8 μg/m3). Contributions of within-room emissions to total PM10 mass in the baby rooms averaged 37–81%. Near-room indoor emissions and outdoor sources contributed 18–59% and 1–5%, respectively. Airborne particle levels in the size range 1–10 μm showed strong dependence on human activities, indicating the importance of indoor-generated particles for infant’s exposure to airborne particulate matter in the NICU.

What should the ventilation objectives be for retrofit energy efficiency interventions of dwellings?

Major energy efficiency refurbishment of the UK housing stock is needed to help attain emission reduction targets of greenhouse gases. Such measures typically entail some planned or incidental reduction of uncontrolled ventilation in dwellings. This paper examines the trade-offs for health and sustainability objectives of typical retrofit refurbishments in UK homes. While reducing ventilation can help protect against the ingress of harmful pollutants from the outdoor air, our results demonstrate that reducing permeability to low levels, without additional purpose-provided ventilation, is likely to lead to substantial increases in pollutants derived from indoor sources, including indoor-generated particles, radon and environmental tobacco smoke. The monetised equivalent cost of the health dis-benefits associated with these exposures may exceed the potential benefits of reducing energy costs and greenhouse gas emissions. Practical application: Reducing uncontrolled ventilation of dwellings helps to improve energy efficiency and can protect against the ingress of pollutants from the outdoor environment. However, simulation studies suggest that at high degrees of airtightness (very low permeability) there is a potentially steep rise in pollutants of indoor origin, whose adverse effects on health may outweigh the benefits of reduced energy use, lower CO2 emissions and protection against outdoor pollution. Though the optimal permeability level for a given dwelling will vary with local circumstances, considerations of health protection suggest the need to avoid reducing permeability to low levels.

Outdoor infiltration and indoor contribution of UFP and BC, OC, secondary inorganic ions and metals in PM2.5 in schools

Infiltration of outdoor-sourced particles into indoor environments in 39 schools in Barcelona was assessed during school hours. Tracers of road traffic emissions (NO2, Equivalent Black Carbon (EBC), Ultrafine Particles (UFP), Sb), secondary inorganic aerosols (SO42−, NO3−, NH4+) and a number of PM2.5 trace elements showed median indoor/outdoor (I/O) ratios ≤ 1, indicating that outdoor sources importantly contributed to indoor concentrations. Conversely, OC and mineral components had I/O ratios>1. Different infiltration factors were found for traffic and secondary components (0.31–0.75 and 0.50–0.92, cold and warm season respectively), with maxima corresponding to EBC and Cd. Higher concentrations of indoor-generated particles were observed when closed windows hindered dispersion (cold season). Building age was not a major determinant of indoor levels. Neither were the window's material, except for NO2 (with an increase of 8 μg m−3 for wood framed windows) and the mineral components (also dependent on the presence of sand in a distance <20m) that reach the indoor environment via soil adhering to footwear with their dispersion being more barred by Aluminium/PVC framed windows than the wooden ones. Enlarged indoor concentrations of some trace elements suggest the presence of indoor sources that should be further investigated in order to achieve a healthier school indoor environment.

Contribution of indoor-generated particles to residential exposure

The majority of airborne particles in residences, when expressed as number concentrations, are generated by the residents themselves, through combustion/thermal related activities. These particles have a considerably smaller diameter than 2.5 μm and, due to the combination of their small size, chemical composition (e.g. soot) and intermittently very high concentrations, should be regarded as having potential to cause adverse health effects.In this study, time resolved airborne particle measurements were conducted for seven consecutive days in 22 randomly selected homes in the urban area of Lund in southern Sweden. The main purpose of the study was to analyze the influence of human activities on the concentration of particles in indoor air. Focus was on number concentrations of particles with diameters <300 nm generated by indoor activities, and how these contribute to the integrated daily residential exposure. Correlations between these particles and soot mass concentration in total dust were also investigated.It was found that candle burning and activities related to cooking (using a frying pan, oven, toaster, and their combinations) were the major particle sources.The frequency of occurrence of a given concentration indoors and outdoors was compared for ultrafine particles. Indoor data was sorted into non-occupancy and occupancy time, and the occupancy time was further divided into non-activity and activity influenced time. It was found that high levels (above 104 cm−3) indoors mainly occur during active periods of occupancy, while the concentration during non-activity influenced time differs very little from non-occupancy time.Total integrated daily residential exposure of ultrafine particles was calculated for 22 homes, the contribution from known activities was 66%, from unknown activities 20%, and from background/non-activity 14%.The collected data also allowed for estimates of particle source strengths for specific activities, and for some activities it was possible to estimate correlations between the number concentration of ultrafine particles and the mass concentration of soot in total dust in 10 homes. Particle source strengths (for 7 specific activities) ranged from 1.6·1012 to 4.5·1012 min−1.The correlation between ultrafine particles and mass concentration of soot in total dust varied between 0.37 and 0.85, with an average of 0.56 (Pearson correlation coefficient).This study clearly shows that due to the importance of indoor sources, residential exposure to ultrafine particles cannot be characterized by ambient measurements alone.

Indoor aerosols: from personal exposure to risk assessment

Motivated by growing considerations of the scale, severity, and risks associated with human exposure to indoor particulate matter, this work reviewed existing literature to: (i) identify state-of-the-art experimental techniques used for personal exposure assessment; (ii) compare exposure levels reported for domestic/school settings in different countries (excluding exposure to environmental tobacco smoke and particulate matter from biomass cooking in developing countries); (iii) assess the contribution of outdoor background vs indoor sources to personal exposure; and (iv) examine scientific understanding of the risks posed by personal exposure to indoor aerosols. Limited studies assessing integrated daily residential exposure to just one particle size fraction, ultrafine particles, show that the contribution of indoor sources ranged from 19% to 76%. This indicates a strong dependence on resident activities, source events and site specificity, and highlights the importance of indoor sources for total personal exposure. Further, it was assessed that 10-30% of the total burden of disease from particulate matter exposure was due to indoor-generated particles, signifying that indoor environments are likely to be a dominant environmental factor affecting human health. However, due to challenges associated with conducting epidemiological assessments, the role of indoor-generated particles has not been fully acknowledged, and improved exposure/risk assessment methods are still needed, together with a serious focus on exposure control.

Indoor airborne particle sources and semi-volatile partitioning effect of outdoor fine PM in offices

To date, few studies have focused on PM air quality in offices, despite the fact that a lot of people spend many working hours a day in such offices. The aim of the present study is to investigate PM1 and PM2.5 in offices in Milan (Northern Italy) and in the air outside those offices. The PM samples were analyzed to determine the entity of certain compounds with possible direct or indirect adverse effects on human health: PAHs, BpA, and water soluble inorganic ions.A good correlation between outdoor and indoor PM mass concentrations emerged (R2 ∼0.87). The maximum I/O concentration ratio was 0.92, suggesting that the indoor PM level was always lower than the outdoor level. The average infiltration factor, FINF, was 0.55, showing that about a half of the outdoor PM had come indoors. The indoor-generated particles, Cig, had values ranging from 0 to 4.4 μg m−3 (<25% of the indoor PM), showing that PM indoor sources had only made a limited contribution to total indoor PM.The results of the indoor-to-outdoor comparisons for the aforementioned chemical compounds demonstrate that the offices were characterized by the absence of effective indoor sources of particulate-bound PAHs and inorganic ions, whereas Cig was around 58% of the indoor concentration for BpA. Our analysis of the FINF data pointed to the presence of a volatilization effect from PM for semi-volatile compounds like ammonium nitrate and 4- or 5-ring PAHs, which affected the measurement of their FINF. We propose the introduction of a new and simple parameter, called volatilization correction, to take account of this effect.

Airborne particulate matter and gaseous air pollutants in residential structures in Lodi province, Italy

The province of Lodi is located in northern Italy on the Po River plain, where high background levels of air pollutants are prevalent. Lodi province is characterized by intensive agriculture, notably animal husbandry. This paper assesses indoor levels of selected airborne pollutants in 60 homes in the province, with special attention to size-fractionated particulate matter (PM). Indoor PM₂.₅ concentrations are frequently higher than current guidelines. PM₁₀ and nitrogen dioxide also exceed the respective guideline recommendations in some cases, noting that 24-h nitrogen dioxide levels were compared with an annual limit value. All other studied pollutant levels are below current international guidelines. Among indoor PM size fractions, PM₀.₅ is predominant in terms of mass concentrations corresponding to 57% of PM₁₀ in summer and 71% in winter. A strong seasonal trend is observed for all studied pollutants, with higher levels in winter corresponding to changes in ambient concentrations. The seasonal variation in PM₁₀ is largely due to PM₀.₅ increase from summer to winter. Summer indoor PM levels are mainly from indoor-generated particles, while particles of outdoor origin represent the main contribution to winter indoor PM levels. On average, indoor concentrations of coarse PM are mostly constituted by indoor-generated particles. This study presents a comparison between measured indoor concentrations in the study area and indoor air quality guideline criteria. Accordingly, particulate matter (PM) and NO₂ are identified as key pollutants that may pose health concerns. It is also found that indoor PM in residential units is mainly constituted by particles with aerodynamic diameters <0.5 μm, especially in winter. Risk mitigation strategies should be focused on the reduction in indoor levels of NO₂ and ultrafine and fine particles, both infiltrated from outdoors and generated by indoor sources.

Use of real-time light scattering data to estimate the contribution of infiltrated and indoor-generated particles to indoor air.

The contribution of outdoor particulate matter (PM) to residential indoor concentrations is currently not well understood. Most importantly, separating indoor PM into indoor- and outdoor-generated components will greatly enhance our knowledge of the outdoor contribution to total indoor and personal PM exposures. This paper examines continuous light scattering data at 44 residences in Seattle, WA. A newly adapted recursive model was used to model outdoor-originated PM entering indoor environments. After censoring the indoor time-series to remove the influence of indoor sources, nonlinear regression was used to estimate particle penetration (P, 0.94 +/- 0.10), air exchange rate (a, 0.54 +/- 0.60 h(-1)), particle decay rate (k, 0.20 +/- 0.16 h(-1)), and particle infiltration (F(inf), 0.65 +/- 0.21) for each of the 44 residences. All of these parameters showed seasonal differences. The F(inf) estimates agree well with those estimated from the sulfur-tracer method (R2 = 0.78). The F(inf) estimates also showed robust and expected behavior when compared against known influencing factors. Among our study residences, outdoor-generated particles accounted for an average of 79 +/- 17% of the indoor PM concentration, with a range of 40-100% at individual residences. Although estimates of P, a, and k were dependent on the modeling technique and constraints, we showed that a recursive mass balance model combined with our censoring algorithms can be used to attribute indoor PM into its outdoor and indoor components and to estimate an average P, a, k, and F(inf), for each residence.

A Pilot Investigation of the Relative Toxicity of Indoor and Outdoor Fine Particles: In Vitro Effects of Endotoxin and Other Particulate Properties

In this study we assessed the in vitro toxicity of 14 paired indoor and outdoor PM(2.5) samples (particulate matter &lt; or =2.5 microm in aerodynamic diameter) collected in 9 Boston-area homes. Samples were collected as part of a large indoor particle characterization study that included the simultaneous measurement of indoor and outdoor PM(2.5), particle size distributions, and compositional data (e.g., elemental/organic carbon, endotoxin, etc.). Bioassays were conducted using rat alveolar macrophages (AMs), and tumor necrosis factor (TNF) was measured to assess particle-induced proinflammatory responses. Additional experiments were also conducted in which AMs were primed with lipopolysaccharides (LPS) to simulate preexisting pulmonary inflammation such as that which might exist in sick and elderly individuals. Significant TNF production above that of negative controls was observed for AMs exposed to either indoor or outdoor PM(2.5). TNF releases were further amplified for primed AMs, suggesting that preexisting inflammation can potentially exacerbate the toxicity of not only outdoor PM(2.5) (as shown by previous studies) but also indoor PM(2.5). In addition, indoor particle TNF production was found to be significantly higher than outdoor particle TNF production in unprimed AMs, both before and after normalization for endotoxin concentrations. Our results suggest that indoor-generated particles may be more bioactive than ambient particles. Endotoxin was demonstrated to mediate proinflammatory responses for both indoor and outdoor PM(2.5), but study findings suggest the presence of other proinflammatory components of fine particles, particularly for indoor-generated particles. Given these study findings and the fact that people spend 85-90% of their time indoors, future studies are needed to address the toxicity of indoor particles.

Characterization of Indoor Particle Sources Using Continuous Mass and Size Monitors

ABSTRACT A comprehensive indoor particle characterization study was conducted in nine Boston-area homes in 1998 in order to characterize sources of PM in indoor environments. State-of-the-art sampling methodologies were used to obtain continuous PM2.5 concentration and size distribution particulate data for both indoor and outdoor air. Study homes, five of which were sampled during two seasons, were monitored over week-long periods. Among other data collected during the extensive monitoring efforts were 24hr elemental/organic carbon (EC/OC) particulate data as well as semi-continuous air exchange rates and time-activity information. This rich data set shows that indoor particle events tend to be brief, intermittent, and highly variable, thus requiring the use of continuous instrumentation for their characterization. In addition to dramatically increasing indoor PM25 concentrations, these data demonstrate that indoor particle events can significantly alter the size distribution and composition of indoor particles. Source event data demonstrate that the impacts of indoor activities are especially pronounced in the ultrafine (da < 0.1 um) and coarse (2.5 < da < 10 |um) modes. Among the sources of ultrafine particles characterized in this study are indoor ozone/terpene reactions. Furthermore, EC/OC data suggest that organic carbon is a major constituent of particles emitted during indoor source events. Whether exposures to indoor-generated particles, particularly from large short-term peak events, may be associated with adverse health effects will become clearer when biological mechanisms are better known.