Abstract  U.S. Environmental Protection Agency. Because human activities impact the timing, location, and degree of pollutant exposure, they play a key role in explaining exposure variation. This fact has motivated the collection of activity pattern data for their specific use in exposure assessments. The largest of these recent efforts is the National Human Activity Pattern Survey (NHAPS), a 2-year probability-based telephone survey (n=9386) of exposure-related human activities in the United States (U.S.) sponsored by the U.S. Environmental Protection Agency (EPA). The primary purpose of NHAPS was to provide comprehensive and current exposure information over broad geographical and temporal scales, particularly for use in probabilistic population exposure models. NHAPS was conducted on a virtually daily basis from late September 1992 through September 1994 by the University of Maryland's Survey Research Center using a computer-assisted telephone interview instrument (CATI) to collect 24-h retrospective diaries and answers to a number of personal and exposure-related questions from each respondent. The resulting diary records contain beginning and ending times for each distinct combination of location and activity occurring on the diary day (i.e., each microenvironment). Between 340 and 1713 respondents of all ages were interviewed in each of the 10 EPA regions across the 48 contiguous states. Interviews were completed in 63% of the households contacted. NHAPS respondents reported spending an average of 87% of their time in enclosed buildings and about 6% of their time in enclosed vehicles. These proportions are fairly constant across the various regions of the U.S. and Canada and for the California population between the late 1980s, when the California Air Resources Board (CARB) sponsored a state-wide activity pattern study, and the mid-1990s, when NHAPS was conducted. However, the number of people exposed to environmental tobacco smoke (ETS) in California seems to have decreased over the same time period, where exposure is determined by the reported time spent with a smoker. In both California and the entire nation, the most time spent exposed to ETS was reported to take place in residential locations.

Abstract  Carbon sequestration by forested ecosystems offers a potential climate change mitigation benefit. However, wildfire has the potential to reverse this benefit. In the western United States, climate change and land management practices have led to increases in wildfire intensity and size. One potential means of reducing carbon emissions from wildfire is the use of prescribed burning, which consumes less biomass and therefore releases less carbon to the atmosphere. This study uses a regional fire emissions model to estimate the potential reduction in fire emissions when prescribed burning is applied in dry, temperate forested systems of the western U.S. Daily carbon dioxide (CO(2)) fire emissions for 2001-2008 were calculated for the western U.S. for two cases: a default wildfire case and one in which prescribed burning was applied. Wide-scale prescribed fire application can reduce CO(2) fire emissions for the western U.S. by 18-25% in the western U.S., and by as much as 60% in specific forest systems. Although this work does not address important considerations such as the feasibility of implementing wide-scale prescribed fire management or the cumulative emissions from repeated prescribed burning, it does provide constraints on potential carbon emission reductions when prescribed burning is used.

Abstract  This report describes a recent analysis of the original ACS cohort, a large ongoing prospective study of mortality in adults that started in 1982 and has played a central role in the setting of National Ambient Air Quality Standards for fine particulate matter pollution in the U.S. as well as assessments of benefits from PM reduction worldwide. The new study describes for the first time work by Dr. Daniel Krewski and colleagues to increase the follow-up period to 18 years (1982 to 2000) and extend the range of analyses to include innovative refinements of statistical methods and incorporate sophisticated control of bias and confounding.

Abstract  Objective: There is limited information on the public health impact of wildfires. The relationship of cardiorespiratory hospital admissions (n = 40 856) to wildfire-related particulate matter (PM2.5) during catastrophic wildfires in southern California in October 2003 was evaluated. Methods: Zip code level PM2.5 concentrations were estimated using spatial interpolations from measured PM2.5, light extinction, meteorological conditions, and smoke information from MODIS satellite images at 250 m resolution. Generalised estimating equations for Poisson data were used to assess the relationship between daily admissions and PM2.5, adjusted for weather, fungal spores (associated with asthma), weekend, zip code-level population and sociodemographics. Results: Associations of 2-day average PM2.5 with respiratory admissions were stronger during than before or after the fires. Average increases of 70 μg/m3 PM2.5 during heavy smoke conditions compared with PM2.5 in the pre-wildfire period were associated with 34% increases in asthma admissions. The strongest wildfire-related PM2.5 associations were for people ages 65–99 years (10.1% increase per 10 μg/m3 PM2.5, 95% CI 3.0% to 17.8%) and ages 0–4 years (8.3%, 95% CI 2.2% to 14.9%) followed by ages 20–64 years (4.1%, 95% CI −0.5% to 9.0%). There were no PM2.5–asthma associations in children ages 5–18 years, although their admission rates significantly increased after the fires. Per 10 μg/m3 wildfire-related PM2.5, acute bronchitis admissions across all ages increased by 9.6% (95% CI 1.8% to 17.9%), chronic obstructive pulmonary disease admissions for ages 20–64 years by 6.9% (95% CI 0.9% to 13.1%), and pneumonia admissions for ages 5–18 years by 6.4% (95% CI −1.0% to 14.2%). Acute bronchitis and pneumonia admissions also increased after the fires. There was limited evidence of a small impact of wildfire-related PM2.5 on cardiovascular admissions. Conclusions: Wildfire-related PM2.5 led to increased respiratory hospital admissions, especially asthma, suggesting that better preventive measures are required to reduce morbidity among vulnerable populations.

Abstract  Background: Although many studies have linked elevations in tropospheric ozone to adverse health outcomes, the effect of long-term exposure to ozone on air pollution–related mortality remains uncertain. We examined the potential contribution of exposure to ozone to the risk of death from cardiopulmonary causes and specifically to death from respiratory causes. Methods: Data from the study cohort of the American Cancer Society Cancer Prevention Study II were correlated with air-pollution data from 96 metropolitan statistical areas in the United States. Data were analyzed from 448,850 subjects, with 118,777 deaths in an 18-year follow-up period. Data on daily maximum ozone concentrations were obtained from April 1 to September 30 for the years 1977 through 2000. Data on concentrations of fine particulate matter (particles that are 2.5 µm in aerodynamic diameter [PM2.5]) were obtained for the years 1999 and 2000. Associations between ozone concentrations and the risk of death were evaluated with the use of standard and multilevel Cox regression models. Results: In single-pollutant models, increased concentrations of either PM2.5 or ozone were significantly associated with an increased risk of death from cardiopulmonary causes. In two-pollutant models, PM2.5 was associated with the risk of death from cardiovascular causes, whereas ozone was associated with the risk of death from respiratory causes. The estimated relative risk of death from respiratory causes that was associated with an increment in ozone concentration of 10 ppb was 1.040 (95% confidence interval, 1.010 to 1.067). The association of ozone with the risk of death from respiratory causes was insensitive to adjustment for confounders and to the type of statistical model used. Conclusions: In this large study, we were not able to detect an effect of ozone on the risk of death from cardiovascular causes when the concentration of PM2.5 was taken into account. We did, however, demonstrate a significant increase in the risk of death from respiratory causes in association with an increase in ozone concentration.

Abstract  The sentiment that woodsmoke, being a natural substance, must be benign to humans is still sometimes heard. It is now well established, however, that wood-burning stoves and fireplaces as well as wildland and agricultural fires emit significant quantities of known health-damaging pollutants, including several carcinogenic compounds. Two of the principal gaseous pollutants in woodsmoke, CO and NOx, add to the atmospheric levels of these regulated gases emitted by other combustion sources. Health impacts of exposures to these gases and some of the other woodsmoke constituents (e.g., benzene) are well characterized in thousands of publications. As these gases are indistinguishable no matter where they come from, there is no urgent need to examine their particular health implications in woodsmoke. With this as the backdrop, this review approaches the issue of why woodsmoke may be a special case requiring separate health evaluation through two questions. The first question we address is whether woodsmoke should be regulated and/or managed separately, even though some of its separate constituents are already regulated in many jurisdictions. The second question we address is whether woodsmoke particles pose different levels of risk than other ambient particles of similar size. To address these two key questions, we examine several topics: the chemical and physical nature of woodsmoke; the exposures and epidemiology of smoke from wildland fires and agricultural burning, and related controlled human laboratory exposures to biomass smoke; the epidemiology of outdoor and indoor woodsmoke exposures from residential woodburning in developed countries; and the toxicology of woodsmoke, based on animal exposures and laboratory tests. In addition, a short summary of the exposures and health effects of biomass smoke in developing countries is provided as an additional line of evidence. In the concluding section, we return to the two key issues above to summarize (1) what is currently known about the health effects of inhaled woodsmoke at exposure levels experienced in developed countries, and (2) whether there exists sufficient reason to believe that woodsmoke particles are sufficiently different to warrant separate treatment from other regulated particles. In addition, we provide recommendations for additional woodsmoke research.

Abstract  Smoke exposure from landscape and coal mine fires can have severe impacts on human health. The ability of health studies to accurately identify potential associations between smoke exposure and health is dependent on the techniques utilised to quantify exposure concentrations for the population at risk. The evolution of spatial modelling techniques capable of better characterising this association has potential to provide more precise health effect estimates. We reviewed the literature to identify and assess the spatial modelling techniques available to estimate smoke PM2.5 or PM10 concentrations from open biomass or coal mine fires. Four electronic databases were searched: MEDLINE, EMBASE, Scopus and Web of Science. Studies were included if they utilised any method for modelling the spatial distribution of PM2.5 or PM10 concentrations from open biomass or coal mine fires and had applied the modelled PM to health data. Studies based on un-adjusted monitoring data, or which were not in English, were excluded. We identified 28 studies which utilised five spatial modelling techniques to assess exposure from open biomass fires: dispersion models, land use regression, satellite remote sensing, spatial interpolation and blended models. No studies of coal mine fires were identified. We found the most effective models combined multiple techniques to enhance the strengths and mitigate the weaknesses of the underlying individual techniques. "Blended" models have the potential to facilitate research in regions currently under represented in biomass or coal mine fire studies as well as enhancing the power of studies to identify associations with health outcomes.

Abstract  The Pacific Northwest 2018 Wildland Fire Season: Summary of key events and issues offers an overview of key lessons and issues from the 2018 fire season. This document gathers key events from sub-regions and from specific fires; synthesizes key data and lessons learned from the events of the season; and shares these insights in a concise format. It may serve as a framework to support future discussions and further analyses.

Abstract  The Tubbs Fire (2017) and Camp Fire (2018) are the first known wildfires where widespread drinking water chemical contamination was discovered in the water distribution network and not in the source water after the fire. In both disasters, drinking water exceeded state and federal government‐defined exposure limits for several volatile organic compound (VOC) contaminants (e.g., benzene at 40,000 µg/L [Tubbs] and >2,217 µg/L [Camp]). This work outlines factors that influence wildfire‐induced drinking water quality threats based on the findings from these two fires and explores related scientific and policy issues. For example, certain plastics in the network may serve as a primary VOC source through in situ plastic pyrolysis. Depressurization of the distribution network likely transported contaminated water that subsequently contaminated undamaged infrastructure. As wildfires at the wildland–urban interface are likely to occur more frequently, greater scientific evidence is needed to guide agency responses that will better protect public health.

Abstract  Biomass combustion is known to be one of the main contributors to air pollution. However, the influence of biomass burning on the distribution of viable bacterial and fungal aerosols is uncertain. This study aimed to examine survivability of bacteria and fungi in the post-combustion products, and to investigate the aerosolization of viable cells during combustion of different types of organic materials. Laboratory experiments included a small-scale combustion of organic materials contaminated with microorganisms in order to determine the survivability of microbes in the combustion products and the potential aerosolization of viable cells during combustion. Field experiments were completed during intentional and prescribed biomass burning events in order to investigate the aerosolization mechanisms that are not available at the laboratory scale. Laboratory experiments did not demonstrate aerosolization of microorganisms during biomass combustion. However, the relatively high survival rate of bacteria in the combustion products ought to be accounted for, as the surviving microorganisms can potentially be aerosolized by high velocity natural air flows. Field investigations demonstrated significant increase in the bioaerosol concentration above natural background during and after biomass combustion.

Abstract  The expected age-class structure of a forest dependent on random periodic fire for disturbance and renewal is derived and presented. It is simply the negative exponential distribution, well known in probability mathematics. An important feature of this concept is that the present age-class structure of such a forest is the key to its past fire history. Its limitations are discussed, and the computer simulation of variations, including the interaction of fire and logging, is described. Three examples of its use in interpreting fire history are given.

Abstract  The TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor satellite (launched on 13 October 2017) is a nadir-viewing spectrometer measuring reflected sunlight in the ultraviolet, visible, near-infrared, and shortwave infrared spectral ranges. The measured spectra are used to retrieve total columns of trace gases, including nitrogen dioxide (NO2). For ground validation of these satellite measurements, Pandora spectrometers, which retrieve high-quality NO2 total columns via direct-sun measurements, are widely used. In this study, Pandora NO2 measurements made at three sites located in or north of the Greater Toronto Area (GTA) are used to evaluate the TROPOMI NO2 data products, including a standard Royal Netherlands Meteorological Institute (KNMI) tropospheric and stratospheric NO2 data product and a TROPOMI research data product developed by Environment and Climate Change Canada (ECCC) using a high-resolution regional air quality forecast model (in the air mass factor calculation). It is found that these current TROPOMI tropospheric NO2 data products (standard and ECCC) met the TROPOMI design bias requirement (< 10 %). Using the statistical uncertainty estimation method, the estimated TROPOMI upper-limit precision falls below the design requirement at a rural site but above in the other two urban and suburban sites. The Pandora instruments are found to have sufficient precision (< 0.02 DU) to perform TROPOMI validation work. In addition to the traditional satellite validation method (i.e., pairing ground-based measurements with satellite measurements closest in time and space), we analyzed TROPOMI pixels located upwind and downwind from the Pandora site. This makes it possible to improve the statistics and better interpret the high-spatial-resolution measurements made by TROPOMI. By using this wind-based validation technique, the number of coincident measurements can be increased by about a factor of 5. With this larger number of coincident measurements, this work shows that both TROPOMI and Pandora instruments can reveal detailed spatial patterns (i.e., horizontal distributions) of local and transported NO2 emissions, which can be used to evaluate regional air quality changes. The TROPOMI ECCC NO2 research data product shows improved agreement with Pandora measurements compared to the TROPOMI standard tropospheric NO2 data product (e.g., lower multiplicative bias at the suburban and urban sites by about 10 %), demonstrating benefits from the high-resolution regional air quality forecast model.

Abstract  The MODerate resolution Imaging Spectroradiometer (MODIS) instrument provides high spatial and spectral resolution views of each point on the earth four times per day. Both Terra and Aqua platforms have a direct broadcast X-band downlink that allows MODIS (Terra) and MODIS/AIRS (Aqua) data to be received in real time by sites having the proper reception hardware. In order to facilitate use of the data, science production software is being freely distributed through the International MODIS/AIRS processing package (IMAPP). The current suite of IMAPP MODIS products includes navigation and calibration (L1B), cloud mask and cloud top properties, including thermodynamic phase, and atmospheric profiles and water vapor retrievals. The applications have been modified from the operational versions running at the Goddard Distributed Active Archive Center (DAAC) such that the only required external toolkit is NCSA HDF4. Distribution of this software provides scientists around the world with the capability to produce local real-time high spatial resolution science products. MODIS data produced from the University of Wisconsin direct broadcast automated processing is used for a variety of science applications, including calibration and product validation. The data is also being used by other institutions for a range of purposes including assisting USA National Weather Service forecasters and the monitoring of Hudson Bay shipping routes by the Canadian Ice Service. The science software is being implemented globally from Australia to South America. IMAPP has been successful in providing a portable, relatively easy to install and user friendly software package for converting direct broadcast MODIS data into valuable science products.

Abstract  Recognition of the growing threat that wildfire smoke poses to public health and safety has resulted in a proactive and determined response led by the USDA-Forest Service (USFS) and enhanced through partnership with many other agencies such as the National Park Service. The Interagency Wildland Fire Air Quality Response Program (IWFAQRP) was created to directly assess, communicate, and address risks posed by wildland fire smoke to the public as well as fire personnel. The program depends on four primary components: specially trained personnel called Air Resource Advisors, air quality monitoring, smoke concentration and dispersion modeling, and coordination and cooperation with agency partners.

Abstract  Wildfires and associated emissions of particulate matter pose significant environmental and health concerns. In this study we propose tools to evaluate building resilience to extreme episodes of outdoor particulate matter using a combination of indoor and outdoor IoT measurements, coupled with survey-based information of occupants' perception and behaviour. We demonstrated the application of the tools on two buildings with different modes of ventilation during the Chico Camp fire event. We characterized the resilience of the buildings on different temporal and spatial scales using the well-established I/O ratio and a newly proposed E-index that evaluates indoor concentration in the context of adopted 24-hour exposure thresholds. Indoor PM2.5 concentration during the entire Chico Camp Fire event was 21 μg/m3 for 4th Street (Mechanically Ventilated) and 36 μg/m3 for Wurster Hall (Naturally Ventilated). The cumulative median I/O ratio during the fire event was 0.27 for 4th Street and 0.67 for Wurster Hall. Overall E-index for 4th Street was 0.82, suggesting that the whole building was resilient to outdoor air pollution while overall E-index was 1.69 for Wurster Hall suggesting that interventions are necessary. The survey revealed that occupant perception of workplace air quality aligns with measured PM2.5 in the two buildings. The results also highlight that a large portion of occupants wore face masks, even though the PM2.5 concentration was below WHO threshold level. The results of our study demonstrate the utility of the proposed IoT-enabled and survey tools to assess the degree of protection from air pollution of outdoor origin for a single building or across a portfolio of buildings. The proposed survey tool also provides direct links between the PM2.5 levels and occupants' perception and behavior.

Abstract  Air quality impacts from wildfires have been dramatic in recent years, with millions of people exposed to elevated and sometimes hazardous fine particulate matter (PM2.5) concentrations for extended periods. Fires emit particulate matter (PM) and gaseous compounds that can negatively impact human health and reduce visibility. While the overall trend in U.S. air quality has been improving for decades, largely due to implementation of the Clean Air Act, seasonal wildfires threaten to undo this in some regions of the United States. Our understanding of the health effects of smoke is growing with regard to respiratory and cardiovascular consequences and mortality. The costs of these health outcomes can exceed the billions already spent on wildfire suppression. In this critical review, we examine each of the processes that influence wildland fires and the effects of fires, including the natural role of wildland fire, forest management, ignitions, emissions, transport, chemistry, and human health impacts. We highlight key data gaps and examine the complexity and scope and scale of fire occurrence, estimated emissions, and resulting effects on regional air quality across the United States. The goal is to clarify which areas are well understood and which need more study. We conclude with a set of recommendations for future research. Implications: In the recent decade the area of wildfires in the United States has increased dramatically and the resulting smoke has exposed millions of people to unhealthy air quality. In this critical review we examine the key factors and impacts from fires including natural role of wildland fire, forest management, ignitions, emissions, transport, chemistry and human health.

Abstract  The NASA Micro-Pulse Lidar Network (MPLNET) is a federated network of Micro-Pulse Lidar (MPL) systems designed to measure aerosol and cloud vertical structure, and boundary layer heights. The data are collected continuously, day and night, over long time periods from sites around the world. Most MPLNET sites are co-located with sites in the NASA Aerosol Robotic Network (AERONET). MPLNET is also a contributing network to the World Meteorological Organization (WMO) Global Atmospheric Watch (GAW) Aerosol Lidar Observation Network, GALION. MPLNET data have contributed to many studies and applications. Key focus areas for MPLNET include: - domestic and international aerosol and cloud research - climate change and air quality studies - support for NASA satellite and sub-orbital missions - aerosol modeling and forecasting MPLNET is composed of NASA sites and others run by, or with help from, partners from around the world. Principal investigators for individual network sites may be from NASA, other US government agencies, universities, or foreign institutions. MPLNET core activities and the NASA staff are funded by the NASA Radiation Sciences Program and the NASA Earth Observing System (EOS). Many individual network sites also have their own funding support.