Coarse particulate matter and airborne endotoxin within wood stove homes

Exposure to fine particulate matter (PM2.5) from non-tobacco sources in homes within high-income countries: a systematic review

The health impacts associated with exposure to elevated concentrations of fine particulate matter (PM_2.5) are well recognised. There is a substantial number of studies characterising PM_2.5 concentrations outdoors, as well as in homes within low- and middle-income countries. In high-income countries (HICs), there is a sizeable literature on indoor PM_2.5 relating to smoking, but the evidence on exposure to PM_2.5 generated from non-tobacco sources in homes is sparse. This is especially relevant as people living in HICs spend the majority of their time at home, and in the northern hemisphere households often have low air exchange rates for energy efficiency. This review identified 49 studies that described indoor PM_2.5 concentrations generated from a variety of common household sources in real-life home settings in HICs. These included wood/solid fuel burning appliances, cooking, candles, incense, cleaning and humidifiers. The reported concentrations varied widely, both between sources and within groups of the same source. The burning of solid fuels was found to generate the highest indoor PM_2.5 concentrations. On occasion, other sources were also reported to be responsible for high PM_2.5 concentrations; however, this was only in a few select examples. This review also highlights the many inconsistencies in the ways data are collected and reported. The variable methods of measurement and reporting make comparison and interpretation of data difficult. There is a need for standardisation of methods and agreed contextual data to make household PM_2.5 data more useful in epidemiological studies and aid comparison of the impact of different interventions and policies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11869-022-01288-8.

Providing a Safe Nest for Improved Health Care Outcomes in Pregnant Women With Asthma

There is a large unmet disease burden arising from asthma in pregnancy. Pregnant women affected by moderate to severe asthma have an increased risk for adverse perinatal outcomes. This can be worsened by social determinants of health, which are social and environmental conditions that affect health and the quality of life. Here we present the case of a medically complex pregnant woman with worsening asthma and challenges in optimizing positive outcomes for both the mother and baby during the perinatal period. This case captures several elements of social determinants of health that affect health outcomes most notably in non-White patients, including chronic exposure to air pollution contributing to asthma severity and reduced access to health care specialists.

Lung-deposited dose of particulate matter from residential exposure to smoke from wood burning

Residential settings are of utmost importance for human exposure, as it is where people spend most of their time. Residential wood combustion is a widespread practice known as a source of indoor particulate matter (PM). Nevertheless, research on the risks of exposure associated with this source is scarce, and a better understanding of respiratory deposition of smoke particles is needed. The dosimetry model ExDoM2 was applied to determine the deposited dose of inhalable particulate matter (PM₁₀) from residential biomass combustion in the human respiratory tract (HRT) of adults and children. The dose was estimated using PM₁₀ exposure concentrations obtained from a field campaign carried out in two households during the operation of an open fireplace and a woodstove. Simultaneously, PM₁₀ levels were monitored outside to investigate the outdoor dose in a rural area strongly impacted by biomass burning emissions. Indoors, the 8-h average PM₁₀ concentrations ranged from 88.3 to 489 μg m^-3 and from 69.4 to 122 μg m^-3 for the operation of the fireplace and the woodstove, respectively, while outdoor average PM₁₀ concentrations ranged from 17.3 to 94.2 μg m^-3. The highest amount of the deposited particles was recorded in the extrathoracic region (68-79%), whereas the deposition was much lower in the tracheobronchial tree (5-6%) and alveolar-interstitial region (16-21%). The total dose received while using the fireplace was more than twofold the one received in the room with a woodstove and more than 10 times higher than in the absence of the source. Overall, indoor doses were higher than the ones received by a subject exposed outdoors, especially at the alveolar-interstitial region. After 24 h of exposure, it was estimated that approximately 35 to 37% of the particles deposited in the HRT were transferred to the gastrointestinal tract, while approximately 2.0-2.5% were absorbed into the blood. The results from exposure and dose of indoor particles gathered in this work suggest that homeowners should be encouraged to upgrade the wood burning technology to reduce the PM levels inside their residences. This study also provides biologically relevant results on the lung deposition of particles from residential biomass burning that can be used as a reference for future research.

Children's Particulate Matter Exposure Characterization as Part of the New Hampshire Birth Cohort Study

As part of the New Hampshire Birth Cohort Study, children 3 to 5 years of age participated in a personal PM_2.5 exposure study. This paper characterizes the personal PM_2.5 exposure and protocol compliance measured with a wearable sensor. The MicroPEM™ collected personal continuous and integrated measures of PM_2.5 exposure and compliance data on 272 children. PM_2.5, black carbon (BC), and brown carbon tobacco smoke (BrC-ETS) exposure was measured from the filters. We performed a multivariate analysis of woodstove presence and other factors that influenced PM_2.5, BC, and BrC exposures. We collected valid exposure data from 258 of the 272 participants (95%). Children wore the MicroPEM for an average of 46% of the 72-h period, and over 80% for a 2-day, 1-night period (with sleep hours counted as non-compliance for this study). Elevated PM_2.5 exposures occurred in the morning, evening, and overnight. Median PM_2.5, BC, and BrC-ETS concentrations were 8.1 μg/m³, 3.6 μg/m³, and 2.4 μg/m³. The combined BC and BrC-ETS mass comprised 72% of the PM_2.5. Woodstove presence, hours used per day, and the primary heating source were associated with the children’s PM_2.5 exposure and air filters were associated with reduced PM_2.5 concentrations. Our findings suggest that woodstove smoke contributed significantly to this cohort’s PM_2.5 exposure. The high sample validity and compliance rate demonstrated that the MicroPEM can be worn by young children in epidemiologic studies to measure their PM_2.5 exposure, inform interventions to reduce the exposures, and improve children’s health.

Effectiveness of portable HEPA air cleaners on reducing indoor endotoxin, PM10, and coarse particulate matter in an agricultural cohort of children with asthma: A randomized intervention trial

We conducted a randomized trial of portable HEPA air cleaners in the homes of children age 6-12 years with asthma in the Yakima Valley, Washington. All families received asthma education while intervention families also received two HEPA cleaners (child's bedroom, living room). We collected 14-day integrated samples of endotoxin in settled dust and PM₁₀ and PM_10-2.5 in the air of the children's bedrooms at baseline and one-year follow-up, and used linear regression to compare follow-up levels, adjusting for baseline. Seventy-one families (36 HEPA, 35 control) completed the study. Baseline geometric mean (GSD) endotoxin loadings were 1565 (6.3) EU/m² and 2110 (4.9) EU/m² , respectively, in HEPA vs. control homes while PM₁₀ and PM_10-2.5 were 22.5 (1.9) μg/m³ and 9.5 (2.9) μg/m³ , respectively, in HEPA homes, and 19.8 (1.8) μg/m³ and 7.7 (2.0) μg/m³ , respectively, in control homes. At follow-up, HEPA families had 46% lower (95% CI, 31%-57%) PM₁₀ on average than control families, consistent with prior studies. In the best-fit heterogeneous slopes model, HEPA families had 49% (95% CI, 6%-110%) and 89% lower (95% CI, 28%-177%) PM_10-2.5 at follow-up, respectively, at 50th and 75th percentile baseline concentrations. Endotoxin loadings did not differ significantly at follow-up (4% lower, HEPA homes; 95% CI, -87% to 50%).

Indoor Particulate Matter in Urban Households: Sources, Pathways, Characteristics, Health Effects, and Exposure Mitigation

Particulate matter (PM) is a complex mixture of solid particles and liquid droplets suspended in the air with varying size, shape, and chemical composition which intensifies significant concern due to severe health effects. Based on the well-established human health effects of outdoor PM, health-based standards for outdoor air have been promoted (e.g., the National Ambient Air Quality Standards formulated by the U.S.). Due to the exchange of indoor and outdoor air, the chemical composition of indoor particulate matter is related to the sources and components of outdoor PM. However, PM in the indoor environment has the potential to exceed outdoor PM levels. Indoor PM includes particles of outdoor origin that drift indoors and particles that originate from indoor activities, which include cooking, fireplaces, smoking, fuel combustion for heating, human activities, and burning incense. Indoor PM can be enriched with inorganic and organic contaminants, including toxic heavy metals and carcinogenic volatile organic compounds. As a potential health hazard, indoor exposure to PM has received increased attention in recent years because people spend most of their time indoors. In addition, as the quantity, quality, and scope of the research have expanded, it is necessary to conduct a systematic review of indoor PM. This review discusses the sources, pathways, characteristics, health effects, and exposure mitigation of indoor PM. Practical solutions and steps to reduce exposure to indoor PM are also discussed.

In vitro toxicity of indoor and outdoor PM10 from residential wood combustion

Particulate matter with aerodynamic diameter < 10 μm (PM₁₀) was collected, indoors and outdoors, when wood burning appliances (open fireplace and woodstove) were in operation. The PM₁₀ ecotoxicity was assessed with the Vibrio fischeri bioluminescence inhibition assay, while the cytotoxicity was evaluated by the WST-8 and lactate dehydrogenase (LDH) release assays using A549 cells. Extracts of PM₁₀-bound polycyclic aromatic hydrocarbons (PAH) were tested for their mutagenicity through the TA98 and TA100 Ames test. The bioluminescent inhibition assay revealed that indoor particles released from the fireplace were the most toxic. Indoors, the reduction in A549 cell metabolic activity was over two times higher for the fireplace in comparison with the woodstove (32 ± 3.2% and 72 ± 7.6% at the highest dose, respectively). Indoor particles from the fireplace were found to induce greater cytotoxicity than the corresponding outdoor samples. Combined WST-8 and LDH results suggest that PM₁₀ exposure induce apoptotic cell death pathway in which the cell membrane integrity is maintained. Indoor and outdoor samples lacked direct and indirect mutagenic activity in any of the tester strains. For indoor-generated PM₁₀, organic carbon and PAH were significantly correlated with cell viability and bioluminescence reduction, suggesting a role of organic compounds in toxicity.

Indoor air quality of 5,000 households and its determinants. Part A: Particulate matter (PM2.5 and PM10-2.5) concentrations in the Japan Environment and Children's Study

Exposure to particulate matter (PM) is one of the important risk factors for morbidity and mortality. Although PM concentrations have been assessed using air quality monitoring stations or modelling, few studies have measured indoor PM in large-scale birth cohorts. The Japan Environment and Children's Study (JECS) measured indoor and outdoor air quality in approximately 5000 households when the participating children were aged 1.5 and 3 years. PM was collected using portable pumps for 7 days (total of 24 h), inside and outside each home. Prediction models for indoor PM concentrations were built using data collected at age 1.5 years and post-validated against data collected at age 3 years. Median indoor/outdoor PM_2.5 and PM_10-2.5 concentrations at age 1.5 years [3 years] were 12.9/12.7 [12.5/11.3] μg/m³ and 5.0/6.3 [5.1/6.1] μg/m³, respectively. Random forest regression analysis found that the major predictors of indoor PM_2.5 were indoor PM_10-2.5, outdoor PM_2.5, indoor smoking, observable smoke and indoor/outdoor temperature. Indoor PM_2.5, outdoor PM_10-2.5, indoor humidity and opening room windows were important predictors of indoor PM_10-2.5 concentrations. Indoor benzene, acetaldehyde, ozone and nitrogen dioxide concentrations were also found to predict indoor PM_2.5 and PM_10-2.5 concentrations, possibly due to the formation of secondary organic aerosols. These findings demonstrate the importance of reducing outdoor PM concentrations, avoiding indoor smoking, using air cleaner in applicable and diminishing sources of VOCs that could form secondary organic aerosols, and the resulting models can be used to predict indoor PM concentrations for the rest of the JECS cohort.

Indoor Air Pollution from Residential Stoves: Examining the Flooding of Particulate Matter into Homes during Real-World Use

This study concerns the levels of particulate matter (PM2.5 and PM1) released by residential stoves inside the home during ‘real world’ use. Focusing on stoves that were certified by the UK’s Department of Environment, Food, and Rural Affairs (DEFRA), PM sensors were placed in the vicinity of 20 different stoves over four weeks, recording 260 uses. The participants completed a research diary in order to provide information on time lit, amount and type of fuel used, and duration of use, among other details. Multivariate statistical tools were used in order to analyse indoor PM concentrations, averages, intensities, and their relationship to aspects of stove management. The study has four core findings. First, the daily average indoor PM concentrations when a stove was used were higher for PM2.5 by 196.23% and PM1 by 227.80% than those of the non-use control group. Second, hourly peak averages are higher for PM2.5 by 123.91% and for PM1 by 133.09% than daily averages, showing that PM is ‘flooding’ into indoor areas through normal use. Third, the peaks that are derived from these ’flooding’ incidents are associated with the number of fuel pieces used and length of the burn period. This points to the opening of the stove door as a primary mechanism for introducing PM into the home. Finally, it demonstrates that the indoor air pollution being witnessed is not originating from outside the home. Taken together, the study demonstrates that people inside homes with a residential stove are at risk of exposure to high intensities of PM2.5 and PM1 within a short period of time through normal use. It is recommended that this risk be reflected in the testing and regulation of residential stoves.

Indoor Exposure to Selected Air Pollutants in the Home Environment: A Systematic Review

(1) Background: There is increasing awareness that the quality of the indoor environment affects our health and well-being. Indoor air quality (IAQ) in particular has an impact on multiple health outcomes, including respiratory and cardiovascular illness, allergic symptoms, cancers, and premature mortality. (2) Methods: We carried out a global systematic literature review on indoor exposure to selected air pollutants associated with adverse health effects, and related household characteristics, seasonal influences and occupancy patterns. We screened records from six bibliographic databases: ABI/INFORM, Environment Abstracts, Pollution Abstracts, PubMed, ProQuest Biological and Health Professional, and Scopus. (3) Results: Information on indoor exposure levels and determinants, emission sources, and associated health effects was extracted from 141 studies from 29 countries. The most-studied pollutants were particulate matter (PM_2.5 and PM₁₀); nitrogen dioxide (NO₂); volatile organic compounds (VOCs) including benzene, toluene, xylenes and formaldehyde; and polycyclic aromatic hydrocarbons (PAHs) including naphthalene. Identified indoor PM_2.5 sources include smoking, cooking, heating, use of incense, candles, and insecticides, while cleaning, housework, presence of pets and movement of people were the main sources of coarse particles. Outdoor air is a major PM_2.5 source in rooms with natural ventilation in roadside households. Major sources of NO₂ indoors are unvented gas heaters and cookers. Predictors of indoor NO₂ are ventilation, season, and outdoor NO₂ levels. VOCs are emitted from a wide range of indoor and outdoor sources, including smoking, solvent use, renovations, and household products. Formaldehyde levels are higher in newer houses and in the presence of new furniture, while PAH levels are higher in smoking households. High indoor particulate matter, NO₂ and VOC levels were typically associated with respiratory symptoms, particularly asthma symptoms in children. (4) Conclusions: Household characteristics and occupant activities play a large role in indoor exposure, particularly cigarette smoking for PM_2.5, gas appliances for NO₂, and household products for VOCs and PAHs. Home location near high-traffic-density roads, redecoration, and small house size contribute to high indoor air pollution. In most studies, air exchange rates are negatively associated with indoor air pollution. These findings can inform interventions aiming to improve IAQ in residential properties in a variety of settings.

Identification of Toxicity Parameters Associated with Combustion Produced Soot Surface Chemistry and Particle Structure by in Vitro Assays

Air pollution has become the world's single biggest environmental health risk of the past decade, causing millions of yearly deaths worldwide. One of the dominant air pollutants is fine particulate matter (PM2.5), which is a product of combustion. Exposure to PM2.5 has been associated with decreased lung function, impaired immunity, and exacerbations of lung disease. Accumulating evidence suggests that many of the adverse health effects of PM2.5 exposure are associated with lung inflammation and oxidative stress. While the physical structure and surface chemistry of PM2.5 are surrogate measures of particle oxidative potential, little is known about their contributions to negative health effects. In this study, we used functionalized carbon black particles as surrogates for atmospherically aged combustion-formed soot to assess the effects of PM2.5 surface chemistry in lung cells. We exposed the BEAS-2B lung epithelial cell line to different soot at a range of concentrations and assessed cell viability, inflammation, and oxidative stress. Our results indicate that exposure to soot with varying particle surface composition results in differential cell viability rates, the expression of pro-inflammatory and oxidative stress genes, and protein carbonylation. We conclude that particle surface chemistry, specifically oxygen content, in soot modulates lung cell inflammatory and oxidative stress responses.

The home air in agriculture pediatric intervention (HAPI) trial: Rationale and methods

BACKGROUND

Data addressing air quality effects on children with asthma in rural U.S. communities are rare. Our community engaged research partnership previously demonstrated associations between neighborhood NH3 and ambient PM2.5 and asthma in the agricultural lower Yakima Valley of Washington. As a next step, the partnership desired an intervention approach to address concerns about pediatric asthma in this largely Latino immigrant, farm worker community.

OBJECTIVE

The Home Air in Agriculture Pediatric Intervention (HAPI) sought to examine the effectiveness of enrichment of an existing asthma education program with portable high-efficiency particulate air (HEPA) cleaners designed to reduce PM2.5 and NH3. We investigated the effect of this enriched approach on these exposures and asthma health measures.

DESIGN

We randomized children with poorly controlled asthma to a control arm (current asthma education program) or an intervention arm (current asthma education program + placement of two indoor air cleaners in the family's home). Outcomes included (1) 14-day integrated samples of indoor air contaminants (PM2.5 and NH3) at baseline and one-year follow-up and (2) child asthma health metrics at baseline, midpoint (4-6 months) and one-year follow-up. These included the Asthma Control Test, symptoms days, clinical utilization, oral corticosteroid use, pulmonary function, fractional exhaled nitric oxide, and urinary leukotriene E4 concentration.

DISCUSSION

To our knowledge, this is the first randomized HEPA cleaner intervention designed to assess NH3 as well as PM2.5 and to evaluate health outcomes of children with asthma in an agricultural region.

Impact of wood combustion on indoor air quality

The incomplete wood combustion in appliances operated in batch mode is a recognised source of both in- and outdoor airborne pollutants, especially particulate matter (PM). Data on pollutant levels and PM characteristics in households with wood burning devices in developed countries are scarce with most studies describing stove change out programmes or other intervention measures. The aim of the present study was to simultaneously evaluate indoor and outdoor concentrations of CO, CO₂ and PM₁₀ during the operation of wood burning appliances (open fireplace and woodstove) in unoccupied rural households. PM₁₀ samples were analysed for water soluble inorganic ions, major and trace elements, organic carbon (OC), elemental carbon (EC), and detailed organic speciation. The CO 8-hour average concentrations did not exceed the protection limit despite the sharp increases observed in relation to background levels. During the open fireplace operation, PM₁₀ levels rose up 12 times compared to background concentrations, while the airtight stove resulted in a 2-fold increase. The inhalation cancer risk of particulate bound PAHs in the room equipped with woodstove was estimated to be negligible while the long-term exposure to PAH levels measured in the fireplace room may contribute to the development of cancer. The excess lifetime cancer risk resulting from the particle-bound Cr(VI) exposure during the fireplace and woodstove operation was higher than 1.0 × 10^-6 and 1.0 × 10^-5, respectively. Levoglucosan was one of the most abundant individual species both indoors and outdoors. This study underlines air pollution hazards and risks arising from the operation of traditional wood burning appliances.

Impact of the wood combustion in an open fireplace on the air quality of a living room: Estimation of the respirable fraction

Presently, both in rural areas and in cities open fireplaces are still present and large quantities of wood are combusted every year. The present study aims to characterize aerosol size distribution, chemical composition and deposition in the human respiratory tract of particles emitted during the combustion of logs of oak in an open fireplace installed in the living room of a typical village house. CO₂ and CO levels and aerosol size distribution have been continuously monitored and a PM₁₀ sampler with two types of filters for chemical and microscopic analysis was also installed. The increment, between the operating periods and the indoor background, in the organic carbon and PM₁₀ concentration due to the use of the fireplace is 15.7±0.6 (mean±standard deviation) and 58.5±6.2μgm^-3, respectively. The two main polluting processes during the operation of the fireplace are the ignition with the subsequent refueling and the final cleaning of the residual ashes. In both phases mean values around 1800 particles cm^-3 with CMD of 0.15μm were measured. However, while PM₁₀ levels of 130±120μgm^-3 were estimated for the ignition stage, values of 200±200μgm^-3 were obtained during the final cleaning step. Assessment conducted according to ISO standard 7708:1995, demonstrated that a person who stays in a living room when an open fireplace is lit will inhale, on average, 217μgm^-3 and 283μgm^-3 during the ignition and the refueling stages, respectively. Subsequent refueling proved to be much less polluting. The ashes removal can also be very polluting and dangerous to health if there are hidden small incandescent embers among the ashes (estimated PM₁₀ of 132μgm^-3), reaching a CO₂ level of 1940ppm and a dangerous level of CO of 132ppm.

Seasonal and spatial variations in the chemical components and the cellular effects of particulate matter collected in Northern China

The health effects of airborne particulate matter (PM) are likely to be strongly influenced by its components. The relationship between the composition of PM and its biological effects has been investigated in vitro/vivo, but more studies are needed to achieve a better understanding of the relationship. Such studies are limited in Northern China, where severe air pollution causes significant health impacts. In this study, we analyzed seasonal PM₁₀ (PM, aerodynamic diameter less than 10μm) samples from five typical cities in Northern China for their physicochemical properties and their in vitro effects on A549 (human lung epithelial cell line) and RAW264.7 (murine monocyte macrophage) cells, including cytotoxicity, oxidative stress and inflammatory effects. Principal component analysis and multiple linear regressions were used to investigate the relationship between the PM components and the cellular responses. The cellular responses of A549 cells were more closely related to the endotoxin content and the levels of polycyclic aromatic hydrocarbons (PAHs) and their derivatives, while the cellular responses of RAW264.7 cells were largely related to PM₁₀-bound metals, and the chalcophile elements (Pb, Cu, Zn, Cd) were more related to the PM-induced oxidative stress, whereas the lithophile and siderophile elements (Al, Fe, Mg, Co, V, Mn, Ca) were more related to PM-induced inflammation and cytotoxicity. As PM compositions changed seasonally, more intense cellular responses were seen when A549 cells were exposed to winter samples that contained higher levels of those components. The autumn and winter samples induced higher levels of oxidative stress in RAW264.7 cells, possibly due to higher contents of chalcophile elements, whereas the spring and/or summer samples were more cytotoxic and proinflammatory, possibly due to higher contents of lithophile and siderophile elements. The study suggests that the evaluation of health impacts induced by air pollution should take into account different physiochemical properties other than the mass concentration, and that public health would benefit greatly from effective, prioritized control of the sources that are the major producers of the central species.

Cell death pathways of particulate matter toxicity

Humans are exposed to various complex mixtures of particulate matter (PM) from different sources. Long-term exposure to high levels of these particulates has been linked to a diverse range of respiratory and cardiovascular diseases that have resulted in hospital admission. The evaluation of the effects of PM exposure on the mechanisms related to cell death has been a challenge for many researchers. Therefore, in this review, we have discussed the effects of airborne PM exposure on mechanisms related to cell death. For this purpose, we have compiled literature data on PM sources, the effects of exposure, and the assays and models used for evaluation, in order to establish comparisons between various studies. The analysis of this collected data suggested divergent responses to PM exposure that resulted in different cell death types (apoptosis, autophagy, and necrosis). In addition, PM induced oxidative stress within cells, which appeared to be an important factor in the determination of cell fate. When the levels of reactive oxygen species were overpowering, the cellular fate was directed toward cell death. This may be the underlying mechanism of the development or exacerbation of respiratory diseases, such as emphysema and chronic obstructive pulmonary diseases. In addition, PM was shown to cause DNA damage and the resulting mutations increased the risk of cancer. Furthermore, several conditions should be considered in the assessment of cell death in PM-exposed models, including the cell culture line, PM composition, and the interaction of the different cells types in in vivo models.

Airborne endotoxin concentrations in indoor and outdoor particulate matter and their predictors in an urban city

Endotoxins are an important biological component of particulate matter and have been associated with adverse effects on human health. There have been some recent studies on airborne endotoxin concentrations. We collected fine (PM_2.5 ) and coarse (PM_10-2.5 ) particulate matter twice on weekdays and weekends each for 48 hour, inside and outside 55 homes in an urban city in Japan. Endotoxin concentrations in both fractions were measured using the kinetic Limulus Amebocyte Lysate assay. The relationships between endotoxin concentrations and household characteristics were evaluated for each fraction. Both indoor and outdoor endotoxin concentrations were higher in PM_2.5 than in PM_10-2.5 . In both PM_2.5 and PM_10-2.5 , indoor endotoxin concentrations were higher than outdoor concentrations, and the indoor endotoxin concentrations significantly correlated with outdoor concentrations in each fraction (R² =0.458 and 0.198, respectively). Indoor endotoxin concentrations in PM_2.5 were significantly higher in homes with tatami or carpet flooring and in homes with pets, and lower in homes that used air purifiers. Indoor endotoxin concentrations in PM_10-2.5 were significantly higher in homes with two or more children and homes with tatami or carpet flooring. These results showed that the indoor endotoxin concentrations were associated with the household characteristics in addition to outdoor endotoxin concentrations.

Reducing indoor air pollutants with air filtration units in wood stove homes

BACKGROUND

Biomass burning has been shown to be a major source of poor indoor air quality (IAQ) in developing and higher income countries across the world. Specifically, wood burning for cooking and heating contributes to high indoor concentrations of fine (particles with aerodynamic diameters<2.5μm; PM_2.5) and coarse (particles with aerodynamic diameters <10μm and >2.5μm; PMc) particulate matter. Endotoxin, predominantly found within the coarse fraction of airborne particulate matter, is associated with proinflammatory effects and adverse outcomes among susceptible populations. The aim of this study was to assess the efficacy of air filter interventions in reducing indoor PM_2.5, PMc, and PMc-associated endotoxin concentrations in homes using a wood stove for primary heating.

RESULTS

Homes (n=48) were randomized to receive in-room air filtration units with either a high efficiency filter (i.e. active) or a lower efficiency fiberglass filter (i.e., placebo). The active filter intervention showed a 66% reduction in indoor PM_2.5 concentrations (95% CI: 42.2% to 79.7% reduction) relative to the placebo intervention. Both the active and the placebo filters were effective in substantially reducing indoor concentrations of PMc (63.3% and 40.6% average reduction for active and placebo filters, respectively) and PMc-associated endotoxin concentrations (91.8% and 80.4% average reductions, respectively).

CONCLUSIONS

These findings support the use of high efficiency air filtration units for reducing indoor PM_2.5 in homes using a wood stove for primary heating. We also discovered that using lower efficiency, lower cost filter alternatives can be effective for reducing PMc and airborne endotoxin in homes burning biomass fuel.

Sources, health effects and control strategies of indoor fine particulate matter (PM2.5): A review

Indoor air quality is directly influenced by indoor PM_2.5. Short-term and long-term exposure of PM_2.5 in the micro environment would severely detriment the health of both humans and animals. The researches both at home and abroad dating from 2000 were analyzed and summarized mainly in the following 3 sections: source apportionment, health effects and control methods. Health effects were illustrated in both epidemiology and toxicology. The epidemiology was explicated in morbidity and mortality, the toxicology was illuminated in inflammatory reaction, oxidative stress, genotoxicity, mutagenicity and carcinogenicity. Control methods were showed in two aspects (sources and means of transmission), of which each was resolved by corresponding control strategy. Abundant investigations indicated that comprehensive control strategies were needed for sources decrement and health burden mitigation of indoor PM_2.5. Based on the increasingly wide research of indoor PM_2.5, the concept of indoors was essentially expanded, and on the basis of the summary of all the aspects mentioned above, both the scope and depth of indoor PM_2.5 research were found insufficiently. Meantime, the potential direction of development in indoor PM_2.5 research were projected, in hope of contributing to further relevant study of engineers in ambient environment and building environment.

Predictors and respiratory depositions of airborne endotoxin in homes using biomass fuels and LPG gas for cooking

Recent studies have highlighted the presence of endotoxin in indoor air and its role in respiratory morbidities. Burning of household fuels including unprocessed wood and dried animal dung could be a major source of endotoxin in homes. We measured endotoxin levels in different size fractions of airborne particles (PM10, PM2.5, and PM1), and estimated the deposition of particle-bound endotoxin in the respiratory tract. The study was carried out in homes burning solid biomass fuel (n=35) and LPG (n=35). Sample filters were analyzed for endotoxin and organic carbon (OC) content. Household characteristics including temperature, relative humidity, and carbon dioxide levels were also recorded. Multivariate regression models were used to estimate the contributing factors for airborne endotoxin. Respiratory deposition doses were calculated using a computer-based model. We found a higher endotoxin concentration in PM2.5 fractions of the particle in both LPG (median: 110, interquartile range (IQR) 100-120 EU/m³) and biomass (median: 350, IQR: 315-430 EU/m³) burning homes. In the multivariate-adjusted model, burning of solid biomass fuel (β: 67; 95% CI: 10.5-124) emerged as the most significant predictor followed by OC (β: 4.7; 95% CI: 2.7-6.8), RH (β: 1.6; 95% CI: 0.76-2.4), and PM2.5 (β: 0.45; 95% CI: 0.11-0.78) for airborne endotoxin (P<0.05). We also observed an interaction between PM organic carbon content and household fuel in predicting the endotoxin levels. The model calculations showed that in biomass burning homes, total endotoxin deposition was higher among infants (59%) than in adult males (47%), of which at least 10% of inhaled endotoxin is deposited in the alveolar region of the lung. These results indicate that fine particles are significant contributors to the deposition of endotoxin in the alveolar region of the lung. Considering the paramount role of endotoxin exposure, and the source and timing of exposure on respiratory health, additional studies are warranted to guide evidence-based public health interventions.

Particulate Matter 2.5 Exposure and Self-Reported Use of Wood Stoves and Other Indoor Combustion Sources in Urban Nonsmoking Homes in Norway

Few studies have examined particulate matter (PM) exposure from self-reported use of wood stoves and other indoor combustion sources in urban settings in developed countries. We measured concentrations of indoor PM < 2.5 microns (PM_2.5) for one week with the MicroPEM^™ nephelometer in 36 households in the greater Oslo, Norway metropolitan area. We examined indoor PM_2.5 levels in relation to use of wood stoves and other combustion sources during a 7 day monitoring period using mixed effects linear models with adjustment for ambient PM_2.5 levels. Mean hourly indoor PM_2.5 concentrations were higher (p = 0.04) for the 14 homes with wood stove use (15.6 μg/m³) than for the 22 homes without (12.6 μg/m³). Moreover, mean hourly PM_2.5 was higher (p = 0.001) for use of wood stoves made before 1997 (6 homes, 20.2 μg/m³), when wood stove emission limits were instituted in Norway, compared to newer wood stoves (8 homes, 11.9 μg/m³) which had mean hourly values similar to control homes. Increased PM_2.5 levels during diary-reported burning of candles was detected independently of concomitant wood stove use. These results suggest that self-reported use of wood stoves, particularly older stoves, and other combustion sources, such as candles, are associated with indoor PM_2.5 measurements in an urban population from a high income country.

Short-term dynamics of indoor and outdoor endotoxin exposure: Case of Santiago, Chile, 2012

Indoor and outdoor endotoxin in PM2.5 was measured for the very first time in Santiago, Chile, in spring 2012. Average endotoxin concentrations were 0.099 and 0.094 [EU/m(3)] for indoor (N=44) and outdoor (N=41) samples, respectively; the indoor-outdoor correlation (log-transformed concentrations) was low: R=-0.06, 95% CI: (-0.35 to 0.24), likely owing to outdoor spatial variability. A linear regression model explained 68% of variability in outdoor endotoxins, using as predictors elemental carbon (a proxy of traffic emissions), chlorine (a tracer of marine air masses reaching the city) and relative humidity (a modulator of surface emissions of dust, vegetation and garbage debris). In this study, for the first time a potential source contribution function (PSCF) was applied to outdoor endotoxin measurements. Wind trajectory analysis identified upwind agricultural sources as contributors to the short-term, outdoor endotoxin variability. Our results confirm an association between combustion particles from traffic and outdoor endotoxin concentrations. For indoor endotoxins, a predictive model was developed but it only explained 44% of endotoxin variability; the significant predictors were tracers of indoor PM2.5 dust (Si, Ca), number of external windows and number of hours with internal doors open. Results suggest that short-term indoor endotoxin variability may be driven by household dust/garbage production and handling. This would explain the modest predictive performance of published models that use answers to household surveys as predictors. One feasible alternative is to increase the sampling period so that household features would arise as significant predictors of long-term airborne endotoxin levels.

Discontinuous and Continuous Indoor Air Quality Monitoring in Homes with Fireplaces or Wood Stoves as Heating System

Around 50% of the world's population, particularly in developing countries, uses biomass as one of the most common fuels. Biomass combustion releases a considerable amount of various incomplete combustion products, including particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs). The paper presents the results of Indoor Air Quality (IAQ) measurements in six houses equipped with wood burning stoves or fireplaces as heating systems. The houses were monitored for 48-h periods in order to collect PM10 samples and measure PAH concentrations. The average, the maximum and the lowest values of the 12-h PM10 concentration were 68.6 μg/m³, 350.7 μg/m³ and 16.8 μg/m³ respectively. The average benzo[a]pyrene 12-h concentration was 9.4 ng/m³, while the maximum and the minimum values were 24.0 ng/m³ and 1.5 ng/m³, respectively. Continuous monitoring of PM10, PAHs, Ultra Fine Particle (UFP) and Total Volatile Organic Compounds (TVOC) was performed in order to study the progress of pollution phenomena due to biomass burning, their trends and contributions to IAQ. The results show a great heterogeneity of impacts on IAQ in terms of magnitude and behavior of the considered pollutants' concentrations. This variability is determined by not only different combustion technologies or biomass quality, but overall by different ignition mode, feeding and flame management, which can also be different for the same house. Moreover, room dimensions and ventilation were significant factors for pollution dispersion. The increase of PM10, UFP and PAH concentrations, during lighting, was always detected and relevant. Continuous monitoring allowed singling out contributions of other domestic sources of considered pollutants such as cooking and cigarettes. Cooking contribution produced an impact on IAQ in same cases higher than that of the biomass heating system.

Indoor particulate matter in rural, wood stove heated homes

Ambient particulate matter (PM) exposures have adverse impacts on public health, but research evaluating indoor PM concentrations in rural homes in the United States using wood as fuel for heating is limited. Our objectives were to characterize indoor PM mass and particle number concentrations (PNCs), quantify infiltration of outdoor PM into the indoor environment, and investigate potential predictors of concentrations and infiltration in 96 homes in the northwestern US and Alaska using wood stoves as the primary source of heating. During two forty-eight hour sampling periods during the pre-intervention winter of a randomized trial, we assessed PM mass (<2.5μm) and PNCs (particles/cm(3)) in six size fractions (0.30-0.49, 0.50-0.99, 1.00-2.49, 2.5-5.0, 5.0-10.0, 10.0+μm). Daily mean (sd) PM2.5 concentrations were 28.8 (28.5)μg/m(3) during the first sampling period and 29.1 (30.1)μg/m(3) during the second period. In repeated measures analyses, household income was inversely associated with PM2.5 and smaller size fraction PNCs, in particular. Time of day was a significant predictor of indoor and outdoor PM2.5 concentrations, and infiltration efficiency was relatively low (Finf (sd)=0.27 (0.20)). Our findings demonstrate relatively high mean PM concentrations in these wood burning homes and suggest potential targets for interventions for improving indoor air quality and health in rural settings.

Estimating the number of low-income americans exposed to household air pollution from burning solid fuels

BACKGROUND

Exposure to household air pollution (HAP) from inefficient biomass and coal stoves kills nearly 4 million people every year worldwide. HAP is an environmental risk associated with poverty that affects an estimated 3 billion people mostly in low- and middle-income countries.

OBJECTIVES

Our goal was to estimate the number of low-income Americans exposed to potentially health-damaging concentrations of HAP.

METHODS

We mapped county-level data for the percentage of households using wood, coal, and/or coke as their primary heating fuel along with percent of the population below the federal poverty level. Using U.S. Census data and the likelihood of fugitive emissions as reported in the literature, we estimated the number of low-income Americans potentially exposed to HAP.

RESULTS

Solid fuel is the primary heating source for > 2.5 million U.S. households, or 6.5 million people. The mapping exercise showed several rural areas, primarily in the northern and western regions, that have high levels of solid-fuel use and poverty. We then identified 117 counties with high co-incident poverty and solid-fuel use as high-priority counties for research into potential health risks from HAP. We estimate that between 500,000 and 600,000 low-income people in the United States are likely exposed to HAP from burning solid fuels within their homes.

CONCLUSION

HAP occurs within the United States and should be further investigated for adverse health risks, especially among those living in areas with rural poverty.

Impact of operating wood-burning fireplace ovens on indoor air quality

The use of combustion heat sources like wood-burning fireplaces has regained popularity in the past years due to increasing energy costs. While the outdoor emissions from wood ovens are strictly regulated in Germany, the indoor release of combustion products is rarely considered. Seven wood burning fireplaces were tested in private homes between November 2012 and March 2013. The indoor air quality was monitored before, during and after operation. The following parameters were measured: ultra-fine particles (5.6-560 nm), fine particles (0.3-20 μm), PM2.5, NOx, CO, CO2, formaldehyde, acetaldehyde, volatile organic compounds (VOCs) and benzo[a]pyrene (BaP). Most ovens were significant sources of particulate matter. In some cases, an increase of benzene and BaP concentrations was observed in the indoor air. The results illustrate that wood-burning fireplaces are potential sources of indoor air contaminants, especially ultra-fine particles. Under the aspect of lowering indoor air exchange rates and increasing the use of fuels with a net zero-carbon footprint, indoor combustion sources are an important topic for the future. With regards to consumer safety, product development and inspection should consider indoor air quality in addition to the present fire protection requirements.

Wintertime particulate mass concentrations in urban environment and the impact of economic crisis

The aim of the specific study is to discuss the impact of economic crisis on air quality in Greece in terms of particulate matter (PM) concentrations. For this purpose, three sampling campaigns were conducted during the winter period of 2012, 2013 and 2014 in two medium sized cities in North Greece (Kavala and Drama). The average concentrations measured ranged from 33-56, 28-47 and 25-44 μg/m(3) for PM10, PM2.5 and PM1, respectively. The analysis of the daily concentration profile for all measurements indicated two distinct periods of elevated concentrations: a) during 08:00 to 10:00 and b) during 19:00 to 22:00. The observed periods of increased concentration coincided with the periods of increased urban traffic in the morning and basic heating needs in late evening. Significant correlation was observed between PM10-PM2.5 (R(2)>0.9) and PM2.5-PM1 (R(2)∼1.0) suggesting that coarse and fine particles originate from similar sources. The PM2.5/PM10 ratio values ranged from 0.84 to 0.85 indicating a major impact of PM2.5 to the final concentration levels recorded. The results presented in the specific study support the notion that a significant alteration is undergoing to the atmospheric air quality in Greece due to the economic crisis and the subsequent increase of biomass products combustion for residential heating. Supplemental materials are available for this article.