Simulating spatio-temporal dynamics of surface PM2.5 emitted from Alaskan wildfires

Wildfire is a major disturbance agent in Arctic boreal and tundra ecosystems that emits large quantities of atmospheric pollutants, including PM2.5. Under the substantial Arctic warming which is two to three times of global average, wildfire regimes in the high northern latitude regions are expected to intensify. This imposes a considerable threat to the health of the people residing in the Arctic regions. Alaska, as the northernmost state of the US, has a sizable rural population whose access to healthcare is greatly limited by a lack of transportation and telecommunication infrastructure and low accessibility. Unfortunately, there are only a few air quality monitoring stations across the state of Alaska, and the air quality of most remote Alaskan communities is not being systematically monitored, which hinders our understanding of the relationship between wildfire emissions and human health within these communities. Models simulating the dispersion of pollutants emitted by wildfires can be extremely valuable for providing spatially comprehensive air quality estimates in areas such as Alaska where the monitoring station network is sparse. In this study, we established a methodological framework that is based on an integration of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, the Wildland Fire Emissions Inventory System (WFEIS), and the Arctic-Boreal Vulnerability Experiment (ABoVE) Wildfire Date of Burning (WDoB) dataset, an Arctic-oriented fire product. Through our framework, daily gridded surface-level PM2.5 concentrations for the entire state of Alaska between 2001 and 2015 for which wildfires are responsible can be estimated. This product reveals the spatio-temporal patterns of the impacts of wildfires on the regional air quality in Alaska, which, in turn, offers a direct line of evidence indicating that wildfire is the dominant driver of PM2.5 concentrations over Alaska during the fire season. Additionally, it provides critical data inputs for research on understanding how wildfires affect human health which creates the basis for the development of effective and efficient mitigation efforts.

Investigating Changes in Ozone Formation Chemistry during Summertime Pollution Events over the Northeastern United States

Understanding the local-scale spatial and temporal variability of ozone formation is crucial for effective mitigation. We combine tropospheric vertical column densities (VCDTrop) of formaldehyde (HCHO) and nitrogen dioxide (NO2), referred to as HCHO-VCDTrop and NO2-VCDTrop, retrieved from airborne remote sensing and the TROPOspheric Monitoring Instrument (TROPOMI) with ground-based measurements to investigate changes in ozone precursors and the inferred chemical production regime on high-ozone days in May-August 2018 over two Northeast urban domains. Over New York City (NYC) and Baltimore/Washington D.C. (BAL/DC), HCHO-VCDTrop increases across the domain, but higher NO2-VCDTrop occurs mainly in urban centers on ozone exceedance days (when maximum daily 8 h average (MDA8) ozone exceeds 70 ppb at any monitor in the region). The ratio of HCHO-VCDTrop to NO2-VCDTrop, proposed as an indicator of the sensitivity of local surface ozone production rates to its precursors, generally increases on ozone exceedance days, implying a transition toward a more NOx-sensitive ozone production regime that should lead to higher efficacy of NOx controls on the highest ozone days in NYC and BAL/DC. Warmer temperatures and enhanced influence from emissions in the local boundary layer on the high-ozone days are accompanied by slower wind speeds in BAL/DC but stronger, southwesterly winds in NYC.

Smoke Injection Heights from Forest and Grassland Fires in Southwest China Observed by CALIPSO

Smoke injection height (SIH) determines the distance and direction of smoke transport, thus impacting the atmospheric environment. In this study, we used Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations data coupled with Moderate Resolution Imaging Spectroradiometer (MODIS) data and the Hybrid Single-Particle Lagrangian Integrated Trajectory model to derive the SIH values during the peak forest and grassland fire seasons from 2012 to 2017 in Southwest China. The results suggest that the SIH values ranged from 2500 m to 2890 m. An analysis of the dependence of SIH on fire characteristics revealed no obvious correlation between SIH and fire radiative power (FRP) because other factors in addition to FRP have an important impact on SIH. Moreover, MODIS FRP data has a drawback in representing the energy released by real fires, also leading to this result. The topographic variables of forest and grassland fires in Southwest China are very different. Complex topography affects SIH by affecting fire intensity and interactions with wind. A comparison of the SIHs with boundary layer height reveals that 75% of the SIHs are above the boundary layer. Compared with other areas, a higher percentage of free troposphere injection occurs in Southwest China, indicating that smoke can cause air pollution over large ranges. Our work provides a better understanding of the transport and vertical distribution of smoke in Southwest China.

An evaluation of empirical and statistically based smoke plume injection height parametrisations used within air quality models

Air quality models are used to assess the impact of smoke from wildland fires, both prescribed and natural, on ambient air quality and human health. However, the accuracy of these models is limited by uncertainties in the parametrisation of smoke plume injection height (PIH) and its vertical distribution. We compared PIH estimates from the plume rise method (Briggs) in the Community Multiscale Air Quality (CMAQ) modelling system with observations from the 2013 California Rim Fire and 2017 prescribed burns in Kansas. We also examined PIHs estimated using alternative plume rise algorithms, model grid resolutions and temporal burn profiles. For the Rim Fire, the Briggs method performed as well or better than the alternatives evaluated (mean bias of less than ±5-20% and root mean square error lower than 1000 m compared with the alternatives). PIH estimates for the Kansas prescribed burns improved when the burn window was reduced from the standard default of 12 h to 3 h. This analysis suggests that meteorological inputs, temporal allocation and heat release are the primary drivers for accurately modelling PIH.

Biomass Burning Over the United States East Coast and Western North Atlantic Ocean: Implications for Clouds and Air Quality

Biomass burning (BB) aerosol events were characterized over the U.S. East Coast and Bermuda over the western North Atlantic Ocean (WNAO) between 2005 and 2018 using a combination of ground-based observations, satellite data, and model outputs. Days with BB influence in an atmospheric column (BB days) were identified using criteria biased toward larger fire events based on anomalously high AERONET aerosol optical depth (AOD) and MERRA-2 black carbon (BC) column density. BB days are present year-round with more in June-August (JJA) over the northern part of the East Coast, in contrast to more frequent events in March-May (MAM) over the southeast U.S. and Bermuda. BB source regions in MAM are southern Mexico and by the Yucatan, Central America, and the southeast U.S. JJA source regions are western parts of North America. Less than half of the BB days coincide with anomalously high PM2.5 levels in the surface layer, according to data from 14 IMPROVE sites over the East Coast. Profiles of aerosol extinction suggest that BB particles can be found in the boundary layer and into the upper troposphere with the potential to interact with clouds. Higher cloud drop number concentration and lower drop effective radius are observed during BB days. In addition, lower liquid water path is found during these days, especially when BB particles are present in the boundary layer. While patterns are suggestive of cloud-BB aerosol interactions over the East Coast and the WNAO, additional studies are needed for confirmation.

Synergistic aircraft and ground observations of transported wildfire smoke and its impact on air quality in New York City during the summer 2018 LISTOS campaign

Air pollution associated with wildfire smoke transport during the summer can significantly affect ozone (O₃) and particulate matter (PM) concentrations, even in heavily populated areas like New York City (NYC). Here, we use observations from aircraft, ground-based lidar, in-situ analyzers and satellite to study and assess wildfire smoke transport, vertical distribution, optical properties, and potential impact on air quality in the NYC urban and coastal areas during the summer 2018 Long Island Sound Tropospheric Ozone Study (LISTOS). We investigate an episode of dense smoke transported and mixed into the planetary boundary layer (PBL) on August 15-17, 2018. The horizontal advection of the smoke is shown to be characterized with the prevailing northwest winds in the PBL (velocity > 10 m/s) based on Doppler wind lidar measurements. The wildfire sources and smoke transport paths from the northwest US/Canada to northeast US are identified from the NOAA hazard mapping system (HMS) fires and smoke product and NOAA-HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) backward trajectory analysis. The smoke particles are distinguished from the urban aerosols by showing larger lidar-ratio (70-sr at 532-nm) and smaller depolarization ratio (0.02) at 1064-nm using the NASA High Altitude Lidar Observatory (HALO) airborne high-spectral resolution lidar (HSRL) measurements. The extinction-related angstrom exponents in the near-infrared (IR at 1020-1640 nm) and Ultraviolet (UV at 340-440 nm) from NASA-Aerosol Robotic Network (AERONET) product show a reverse variation trend along the smoke loadings, and their absolute differences indicate strong correlation with the smoke-Aerosol Optical Depth (AOD) (R > 0.94). We show that the aloft smoke plumes can contribute as much as 60-70% to the column AOD and that concurrent high-loadings of O₃, carbon monoxide (CO), and black carbon (BC) were found in the elevated smoke layers from the University of Maryland (UMD) aircraft in-situ observations. Meanwhile, the surface PM_2.5 (PM with diameter ≤ 2.5 μm), organic carbon (OC) and CO measurements show coincident and sharp increase (e.g., PM_2.5 from 5 μg/m³ before the plume intrusion to ~30 μg/m³) with the onset of the plume intrusions into the PBL along with hourly O₃ exceedances in the NYC region. We further evaluate the NOAA-National Air Quality Forecasting Capability (NAQFC) model PBL-height, PM_2.5, and O₃ with the observations and demonstrate good consistency near the ground during the convective PBL period, but significant bias at other times. The aloft smoke layers are sometimes missed by the model.

Wildfire Smoke Particle Properties and Evolution, From Space-Based Multi-Angle Imaging II: The Williams Flats Fire during the FIREX-AQ Campaign

Although the characteristics of biomass burning events and the ambient ecosystem determine emitted smoke composition, the conditions that modulate the partitioning of black carbon (BC) and brown carbon (BrC) formation are not well understood, nor are the spatial or temporal frequency of factors driving smoke particle evolution, such as hydration, coagulation, and oxidation, all of which impact smoke radiative forcing. In situ data from surface observation sites and aircraft field campaigns offer deep insight into the optical, chemical, and microphysical traits of biomass burning (BB) smoke aerosols, such as single scattering albedo (SSA) and size distribution, but cannot by themselves provide robust statistical characterization of both emitted and evolved particles. Data from the NASA Earth Observing System’s Multi-Angle Imaging SpectroRadiometer (MISR) instrument can provide at least a partial picture of BB particle properties and their evolution downwind, once properly validated. Here we use in situ data from the joint NOAA/NASA 2019 Fire Influence on Regional to Global Environments Experiment-Air Quality (FIREX-AQ) field campaign to assess the strengths and limitations of MISR-derived constraints on particle size, shape, light-absorption, and its spectral slope, as well as plume height and associated wind vectors. Based on the satellite observations, we also offer inferences about aging mechanisms effecting downwind particle evolution, such as gravitational settling, oxidation, secondary particle formation, and the combination of particle aggregation and condensational growth. This work builds upon our previous study, adding confidence to our interpretation of the remote-sensing data based on an expanded suite of in situ measurements for validation. The satellite and in situ measurements offer similar characterizations of particle property evolution as a function of smoke age for the 06 August Williams Flats Fire, and most of the key differences in particle size and absorption can be attributed to differences in sampling and changes in the plume geometry between sampling times. Whereas the aircraft data provide validation for the MISR retrievals, the satellite data offer a spatially continuous mapping of particle properties over the plume, which helps identify trends in particle property downwind evolution that are ambiguous in the sparsely sampled aircraft transects. The MISR data record is more than two decades long, offering future opportunities to study regional wildfire plume behavior statistically, where aircraft data are limited or entirely lacking.

The association between wildfire smoke exposure and asthma-specific medical care utilization in Oregon during the 2013 wildfire season

Wildfire smoke (WFS) increases the risk of respiratory hospitalizations. We evaluated the association between WFS and asthma healthcare utilization (AHCU) during the 2013 wildfire season in Oregon. WFS particulate matter ≤ 2.5 μm in diameter (PM2.5) was estimated using a blended model of in situ monitoring, chemical transport models, and satellite-based data. Asthma claims and place of service were identified from Oregon All Payer All Claims data from 1 May 2013 to 30 September 2013. The association with WFS PM2.5 was evaluated using time-stratified case-crossover designs. The maximum WFS PM2.5 concentration during the study period was 172 µg/m3. A 10 µg/m3 increase in WFS increased risk in asthma diagnosis at emergency departments (odds ratio [OR]: 1.089, 95% confidence interval [CI]: 1.043-1.136), office visit (OR: 1.050, 95% CI: 1.038-1.063), and outpatient visits (OR: 1.065, 95% CI: 1.029-1.103); an association was observed with asthma rescue inhaler medication fills (OR: 1.077, 95% CI: 1.065-1.088). WFS increased the risk for asthma morbidity during the 2013 wildfire season in Oregon. Communities impacted by WFS could see increases in AHCU for tertiary, secondary, and primary care.

Long-range transported North American wildfire aerosols observed in marine boundary layer of eastern North Atlantic

Wildfire is a major source of biomass burning aerosols, which greatly impact Earth climate. Tree species in North America (NA) boreal forests can support high-intensity crown fires, resulting in elevated injection height and longer lifetime (on the order of months) of the wildfire aerosols. Given the long lifetime, the properties of aged NA wildfire aerosols are required to understand and quantify their effects on radiation and climate. Here we present comprehensive characterization of climatically relevant properties, including optical properties and cloud condensation nuclei (CCN) activities of aged NA wildfire aerosols, emitted from the record-breaking Canadian wildfires in August 2017. Despite the extreme injection height of ~12 km, some of the wildfire plumes descended into the marine boundary layer in the eastern North Atlantic over a period of ~2 weeks, owing to the dry intrusions behind mid-latitude cyclones. The aged wildfire aerosols have high single scattering albedos at 529 nm (ω₅₂₉; 0.92-0.95) while low absorption Ångström exponents (Å_abs) at 464 nm/648 nm (0.7-0.9). In comparison, Å_abs of fresh/slightly aged ones are typically 1.4-3.5. This low Å_abs indicates a nearly complete loss of brown carbon, likely due to bleaching and/or evaporation, during the long-range transport. The nearly complete loss suggests that on global average, direct radiative forcing of BrC may be minor. Combining Mie calculations and the measured aerosol hygroscopicity, volatility and size distributions, we show that the high ω₅₂₉ and low Å_abs values are best explained by an external mixture of non-absorbing organic particles and absorbing particles of large BC cores (>~110 nm diameter) with thick non-absorbing coatings. The accelerated descent of the wildfire plume also led to strong increase of CCN concentration at the supersaturation levels representative of marine low clouds. The hygroscopicity parameter, κ_CCN, of the aged wildfire aerosols varies from 0.2 to 0.4, substantially lower than that of background marine boundary layer aerosols. However, the high fraction of particles with large diameter (i.e., within accumulation size ranges, ~100-250 nm) compensates for the low values of κ, and as a result, the aged NA wildfire aerosols contribute more efficiently to CCN population. These results provide direct evidence that the long-range transported NA wildfires can strongly influence CCN concentration in remote marine boundary layer, therefore the radiative properties of marine low clouds. Given the expected increases of NA wildfire intensity and frequency and regular occurrence of dry intrusion following mid-latitude cyclones, the influence of NA wildfire aerosols on CCN and clouds in remote marine environment need to be further examined.

Impact of Fire Emissions on U.S. Air Quality from 1997 to 2016–A Modeling Study in the Satellite Era

A regional modeling system that integrates the state-of-the-art emissions processing (SMOKE), climate (CWRF), and air quality (CMAQ) models has been combined with satellite measurements of fire activities to assess the impact of fire emissions on the contiguous United States (CONUS) air quality during 1997–2016. The system realistically reproduced the spatiotemporal distributions of the observed meteorology and surface air quality, with a slight overestimate of surface ozone (O3) by ~4% and underestimate of surface PM2.5 by ~10%. The system simulation showed that the fire impacts on primary pollutants such as CO were generally confined to the fire source areas but its effects on secondary pollutants like O3 spread more broadly. The fire contribution to air quality varied greatly during 1997-2016 and occasionally accounted for more than 100 ppbv of monthly mean surface CO and over 20 µg m−3 of monthly mean PM2.5 in the Northwest U.S. and Northern California, two regions susceptible to frequent fires. Fire emissions also had implications on air quality compliance. From 1997 to 2016, fire emissions increased surface 8-hour O3 standard exceedances by 10% and 24-hour PM2.5 exceedances by 33% over CONUS.

Wildfire Smoke Particle Properties and Evolution, from Space-Based Multi-Angle Imaging

Emitted smoke composition is determined by properties of the biomass burning source and ambient ecosystem. However, conditions that mediate the partitioning of black carbon (BC) and brown carbon (BrC) formation, as well as the spatial and temporal factors that drive particle evolution, are not understood adequately for many climate and air-quality related modeling applications. In situ observations provide considerable detail about aerosol microphysical and chemical properties, although sampling is extremely limited. Satellites offer the frequent global coverage that would allow for statistical characterization of emitted and evolved smoke, but generally lack microphysical detail. However, once properly validated, data from the National Aeronautics and Space Administration (NASA) Earth Observing System’s Multi-Angle Imaging Spectroradiometer (MISR) instrument can create at least a partial picture of smoke particle properties and plume evolution. We use in situ data from the Department of Energy’s Biomass Burning Observation Project (BBOP) field campaign to assess the strengths and limitations of smoke particle retrieval results from the MISR Research Aerosol (RA) retrieval algorithm. We then use MISR to characterize wildfire smoke particle properties and to identify the relevant aging factors in several cases, to the extent possible. The RA successfully maps qualitative changes in effective particle size, light absorption, and its spectral dependence, when compared to in situ observations. By observing the entire plume uniformly, the satellite data can be interpreted in terms of smoke plume evolution, including size-selective deposition, new-particle formation, and locations within the plume where BC or BrC dominates.

Investigate Wildfire Impacts on Ozone Production by Vertical Observations and Photochemical Modeling

In troposphere, ozone is a toxic secondary pollutant produced when its precursors react in sunlight. An important source of ozone precursors is biomass burning. Here we investigate the impacts of 2016 Southeast U.S. Wildfires on ozone production by integrating vertical resolved ozone profiles and photochemical modeling. The results show that wildfires contributed to ozone lamina at the top of boundary layer and enhanced surface ozone up to about 10ppbv in Southeast U.S.. Ozone lidar observed a lower ozone change with respect to a fast growth of aerosol plume, of which the reason is also investigated. Current results indicate an effective integration of vertical observations and modeling for us to understand the ozone production from fires in troposphere.

Aging Effects on Biomass Burning Aerosol Mass and Composition: A Critical Review of Field and Laboratory Studies

Biomass burning is a major source of atmospheric particulate matter (PM) with impacts on health, climate, and air quality. The particles and vapors within biomass burning plumes undergo chemical and physical aging as they are transported downwind. Field measurements of the evolution of PM with plume age range from net decreases to net increases, with most showing little to no change. In contrast, laboratory studies tend to show significant mass increases on average. On the other hand, similar effects of aging on the average PM composition (e.g., oxygen-to-carbon ratio) are reported for lab and field studies. Currently, there is no consensus on the mechanisms that lead to these observed similarities and differences. This review summarizes available observations of aging-related biomass burning aerosol mass concentrations and composition markers, and discusses four broad hypotheses to explain variability within and between field and laboratory campaigns: (1) variability in emissions and chemistry, (2) differences in dilution/entrainment, (3) losses in chambers and lines, and (4) differences in the timing of the initial measurement, the baseline from which changes are estimated. We conclude with a concise set of research needs for advancing our understanding of the aging of biomass burning aerosol.

Experimental Design of a Prescribed Burn Instrumentation

Observational data collected during experiments, such as the planned Fire and Smoke Model Evaluation Experiment (FASMEE), are critical for evaluating and transitioning coupled fire-atmosphere models like WRF-SFIRE and WRF-SFIRE-CHEM into operational use. Historical meteorological data, representing typical weather conditions for the anticipated burn locations and times, have been processed to initialize and run a set of simulations representing the planned experimental burns. Based on an analysis of these numerical simulations, this paper provides recommendations on the experimental setup such as size and duration of the burns, and optimal sensor placement. New techniques are developed to initialize coupled fire-atmosphere simulations with weather conditions typical of the planned burn locations and times. The variation and sensitivity analysis of the simulation design to model parameters performed by repeated Latin Hypercube Sampling is used to assess the locations of the sensors. The simulations provide the locations for the measurements that maximize the expected variation of the sensor outputs with varying the model parameters.

Biomass Burning Smoke Climatology of the United States: Implications for Particulate Matter Air Quality

We utilize the NOAA Hazard Mapping System smoke product for the period of 2005 to 2016 to develop climatology of smoke occurrence over the Continental United States (CONUS) region and to study the impact of wildland fires on particulate matter air quality at the surface. Our results indicate that smoke is most frequently found over the Great Plains and western states during the summer months. Other hotspots of smoke occurrence are found over state and national parks in the southeast during winter and spring, in the Gulf of Mexico southwards of the Texas and Louisiana coastline during spring season and along the Mississippi River Delta during the fall season. A substantial portion (20%) of the 24 h federal standard for particulate pollution exceedance events in the CONUS region occur when smoke is present. If the U.S. Environmental Protection Agency regulations continue to reduce anthropogenic emissions, wildland fire emissions will become the major contributor to particulate pollution and exceedance events. In this context, we show that HMS smoke product is a valuable tool for analysis of exceptional events caused by wildland fires and our results indicate that these tools can be valuable for policy and decision makers.

The MERRA-2 Aerosol Reanalysis, 1980 Onward. Part II: Evaluation and Case Studies

The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), is NASA's latest reanalysis for the satellite era (1980 onward) using the Goddard Earth Observing System, version 5 (GEOS-5), Earth system model. MERRA-2 provides several improvements over its predecessor (MERRA-1), including aerosol assimilation for the entire period. MERRA-2 assimilates bias-corrected aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer and the Advanced Very High Resolution Radiometer instruments. Additionally, MERRA-2 assimilates (non bias corrected) AOD from the Multiangle Imaging SpectroRadiometer over bright surfaces and AOD from Aerosol Robotic Network sunphotometer stations. This paper, the second of a pair, summarizes the efforts to assess the quality of the MERRA-2 aerosol products. First, MERRA-2 aerosols are evaluated using independent observations. It is shown that the MERRA-2 absorption aerosol optical depth (AAOD) and ultraviolet aerosol index (AI) compare well with Ozone Monitoring Instrument observations. Next, aerosol vertical structure and surface fine particulate matter (PM_2.5) are evaluated using available satellite, aircraft, and ground-based observations. While MERRA-2 generally compares well to these observations, the assimilation cannot correct for all deficiencies in the model (e.g., missing emissions). Such deficiencies can explain many of the biases with observations. Finally, a focus is placed on several major aerosol events to illustrate successes and weaknesses of the AOD assimilation: the Mount Pinatubo eruption, a Saharan dust transport episode, the California Rim Fire, and an extreme pollution event over China. The article concludes with a summary that points to best practices for using the MERRA-2 aerosol reanalysis in future studies.

Observations and impacts of transported Canadian wildfire smoke on ozone and aerosol air quality in the Maryland region on June 9-12, 2015

Canadian wildfire smoke impacted air quality across the northern Mid-Atlantic (MA) of the United States during June 9-12, 2015. A multiday exceedance of the new 2015 70-ppb National Ambient Air Quality Standard (NAAQS) for ozone (O3) followed, resulting in Maryland being incompliant with the Environmental Protection Agency's (EPA) revised 2015 O3 NAAQS. Surface in situ, balloon-borne, and remote sensing observations monitored the impact of the wildfire smoke at Maryland air quality monitoring sites. At peak smoke concentrations in Maryland, wildfire-attributable volatile organic compounds (VOCs) more than doubled, while non-NOx oxides of nitrogen (NOz) tripled, suggesting long range transport of NOx within the smoke plume. Peak daily average PM2.5 was 32.5 µg m(-3) with large fractions coming from black carbon (BC) and organic carbon (OC), with a synonymous increase in carbon monoxide (CO) concentrations. Measurements indicate that smoke tracers at the surface were spatially and temporally correlated with maximum 8-hr O3 concentrations in the MA, all which peaked on June 11. Despite initial smoke arrival late on June 9, 2015, O3 production was inhibited due to ultraviolet (UV) light attenuation, lower temperatures, and nonoptimal surface layer composition. Comparison of Community Multiscale Air Quality (CMAQ) model surface O3 forecasts to observations suggests 14 ppb additional O3 due to smoke influences in northern Maryland. Despite polluted conditions, observations of a nocturnal low-level jet (NLLJ) and Chesapeake Bay Breeze (BB) were associated with decreases in O3 in this case. While infrequent in the MA, wildfire smoke may be an increasing fractional contribution to high-O3 days, particularly in light of increased wildfire frequency in a changing climate, lower regional emissions, and tighter air quality standards.

IMPLICATIONS

The presented event demonstrates how a single wildfire event associated with an ozone exceedance of the NAAQS can prevent the Baltimore region from complying with lower ozone standards. This relatively new problem in Maryland is due to regional reductions in NOx emissions that led to record low numbers of ozone NAAQS violations in the last 3 years. This case demonstrates the need for adequate means to quantify and justify ozone impacts from wildfires, which can only be done through the use of observationally based models. The data presented may also improve future air quality forecast models.

Smoke in the City: How Often and Where Does Smoke Impact Summertime Ozone in the United States?

We investigate the influence of smoke on ozone (O3) abundances over the contiguous United States. Using colocated observations of particulate matter and the National Weather Service Hazard Mapping System smoke data, we identify summertime days between 2005 and 2014 that Environmental Protection Agency Air Quality System O3 monitors are influenced by smoke. We compare O3 mixing ratio distributions for smoke-free and smoke-impacted days for each monitor, while controlling for temperature. This analysis shows that (i) the mean O3 abundance measured on smoke-impacted days is higher than on smoke-free days, and (ii) the magnitude of the effect varies by location with a range of 3 to 36 ppbv. For each site, we present the percentage of days when the 8-h average O3 mixing ratio (MDA8) exceeds 75 ppbv and smoke is present. Smoke-impacted O3 mixing ratios are most elevated in locations with the highest emissions of nitrogen oxides. The Northeast corridor, Dallas, Houston, Atlanta, Birmingham, and Kansas City stand out as having smoke present 10-20% of the days when 8-h average O3 mixing ratios exceed 75 ppbv. Most U.S. cities maintain a similar proportion of smoke-impacted exceedance days when they are held against the new MDA8 limit of 70 ppbv.

Episodic Impacts from California Wildfires Identified in Las Vegas Near-Road Air Quality Monitoring

Air pollutant concentrations near major highways are usually attributed to a combination of nearby traffic emissions and regional background, and generally presumed to be additive in nature. During a near-road measurement study conducted in Las Vegas, NV, the effects of distant wildfires on regional air quality were indicated over a several day period in the summer of 2009. Area-wide elevated particulate levoglucosan (maximum of 0.83 μg/m(3)) and roadside measurements of ultraviolet light-absorbing particulate matter (UVPM) in comparison to black carbon (Delta-C) were apparent over the three-day period. Back-trajectory modeling and satellite images supported the measurement results and indicated the transport of air pollutants from wildfires burning in southern California. Separating roadside measurements under apparent biomass burning event (Delta-C > 1000 ng m(-3)) and nonevent (Delta-C < 1000 ng m(-3)) periods, and constraining to specific days of week, wind speed range, wind direction from the road and traffic volume range, roadside carbon monoxide, black carbon, total particle number count (20-200 nm), and accumulation mode particle number count (100-200 nm) increased by 65%, 146%, 58%, and 366%, respectively, when biomass smoke was indicated. Meanwhile, ultrafine particles (20-100 nm) decreased by 35%. This episode indicates that the presence of aged wildfire smoke may interact with freshly emitted ultrafine particles, resulting in a decrease of particles in the ultrafine mode.

The implementation of NEMS GFS Aerosol Component (NGAC) Version 1.0 for global dust forecasting at NOAA/NCEP

The NOAA National Centers for Environmental Prediction (NCEP) implemented NEMS GFS Aerosol Component (NGAC) for global dust forecasting in collaboration with NASA Goddard Space Flight Center (GSFC). NGAC Version 1.0 has been providing 5 day dust forecasts at 1°×1° resolution on a global scale, once per day at 00:00 Coordinated Universal Time (UTC), since September 2012. This is the first global system capable of interactive atmosphere aerosol forecasting at NCEP. The implementation of NGAC V1.0 reflects an effective and efficient transitioning of NASA research advances to NCEP operations, paving the way for NCEP to provide global aerosol products serving a wide range of stakeholders as well as to allow the effects of aerosols on weather forecasts and climate prediction to be considered.

Aerosol optical properties under the condition of heavy haze over an urban site of Beijing, China

In January 2013, several serious haze pollution events happened in North China. Cimel sunphotometer measurements at an urban site of Beijing (Chinese Academy of Meteorological Sciences-CAMS) from 1 to 30 January 2013 were used to investigate the detailed variation of aerosol optical properties. It was found that Angstrom exponents were mostly larger than 0.80 when aerosol optical depth values are higher than 0.60 at the urban region of Beijing during January 2013. The aerosol optical depth (AOD) at the urban region of Beijing can remain steady at approximately 0.40 before haze happening and then increased sharply to more than 1.50 at 500 nm with the onset of haze, which suggests that the fine-mode AOD is a factor of 20 of the coarse-mode AOD during a serious haze pollution event. The single scattering albedo was approximately 0.90 ± 0.03 at 440, 675, 870 and 1,020 nm during the haze pollution period. The single scattering albedo at 440 nm as a function of the fine-mode fraction was relatively consistent, but it was highly variable at 675, 870 and 1,020 nm. Except on January 12 and 18, all the fine-mode particle volumes were larger than those of coarse particles, which suggests that fine particles from anthropogenic activities made up most of the haze. Aerosol type classification analysis showed that the dominant aerosol types can be classified as both "mixed" and "urban/industrial (U/I) and biomass burning (BB)" categories during the heavy haze period of Beijing in January of 2013. The mixed category occurrence was about 31 %, while the U/I and BB was about 69 %.

Downwind O3 and PM2.5 speciation during the wildfires in 2002 and 2010

A series of wildfires in northern Quebec, early July 2002, and in southern Quebec, late May 2010, resulted in severe air pollution downwind. Downwind exposures were investigated to estimate the impact on outdoor and indoor environments. The plumes derived from the wildfires resulted in an increase of over 10 ppbv ozone (O3) concentrations in both major cities and rural areas, while O3 enhancement was not observed at locations adjacent to wildfire burning areas. Temporal trend in PM2.5 concentration showed a peak of 105.5 μg/m3 on July 7, 2002, while on May 31, 2010 the peak was 151.1 μg/m3 in Boston downwind. PM2.5 speciation showed similar trends between the episodes, along with spikes in the PM2.5/PM10 ratio, and in the concentrations of Black Carbon, ΔC (i.e., UV absorbing compounds minus Black Carbon), Organic Carbon (OC), potassium, and chlorine. OC was the most dominant constituent of the PM2.5 mass in the wildfires. The dominant specific carbon fractions include OC fraction 3, pyrolysis carbon, and EC fraction 1, likely due to pyrolysis of structural components of wood. Indoor PM2.5 peaks at two houses corresponded well with the ambient PM2.5 peak, along with the elemental composition, which could indicate an impact of wildfires on indoor air pollution exposure.

Atmospheric peroxyacetyl nitrate (PAN): a global budget and source attribution

Peroxyacetyl nitrate (PAN) formed in the atmospheric oxidation of non-methane volatile organic compounds (NMVOCs) is the principal tropospheric reservoir for nitrogen oxide radicals (NOx = NO + NO2). PAN enables the transport and release of NOx to the remote troposphere with major implications for the global distributions of ozone and OH, the main tropospheric oxidants. Simulation of PAN is a challenge for global models because of the dependence of PAN on vertical transport as well as complex and uncertain NMVOC sources and chemistry. Here we use an improved representation of NMVOCs in a global 3-D chemical transport model (GEOS-Chem) and show that it can simulate PAN observations from aircraft campaigns worldwide. The immediate carbonyl precursors for PAN formation include acetaldehyde (44% of the global source), methylglyoxal (30 %), acetone (7 %), and a suite of other isoprene and terpene oxidation products (19 %). A diversity of NMVOC emissions is responsible for PAN formation globally including isoprene (37 %) and alkanes (14 %). Anthropogenic sources are dominant in the extratropical Northern Hemisphere outside the growing season. Open fires appear to play little role except at high northern latitudes in spring, although results are very sensitive to plume chemistry and plume rise. Lightning NOx is the dominant contributor to the observed PAN maximum in the free troposphere over the South Atlantic.

Environmental health indicators of climate change for the United States: findings from the State Environmental Health Indicator Collaborative

OBJECTIVE

To develop public health adaptation strategies and to project the impacts of climate change on human health, indicators of vulnerability and preparedness along with accurate surveillance data on climate-sensitive health outcomes are needed. We researched and developed environmental health indicators for inputs into human health vulnerability assessments for climate change and to propose public health preventative actions.

DATA SOURCES

We conducted a review of the scientific literature to identify outcomes and actions that were related to climate change. Data sources included governmental and nongovernmental agencies and the published literature.

DATA EXTRACTION

Sources were identified and assessed for completeness, usability, and accuracy. Priority was then given to identifying longitudinal data sets that were applicable at the state and community level.

DATA SYNTHESIS

We present a list of surveillance indicators for practitioners and policy makers that include climate-sensitive health outcomes and environmental and vulnerability indicators, as well as mitigation, adaptation, and policy indicators of climate change.

CONCLUSIONS

A review of environmental health indicators for climate change shows that data exist for many of these measures, but more evaluation of their sensitivity and usefulness is needed. Further attention is necessary to increase data quality and availability and to develop new surveillance databases, especially for climate-sensitive morbidity.

Influence of fires on O3 concentrations in the western U.S

Because forest fires emit substantial NOx and hydrocarbons--known contributors to O3 production--we hypothesize that interannual variation in western U.S. O3 is related to the burned area. To evaluate this hypothesis we used a gridded database of western U.S. summer burned area (BA) and biomass consumed (BC) by fires between 101-125 degrees W. The fire data were compared with daytime summer O3 mixing ratios from nine rural Clean Air Status and Trends Network (CASTNET) and National Park Service (NPS) sites. Large fire years exhibited widespread enhanced O3. The summer BA was significantly correlated with O3 at all sites. For each 1 million acres burned in the western U.S. during summer, we estimate that the daytime mean O3 was enhanced across the region by 2.0 ppbv. For mean and maximum fire years, O3 was enhanced by an average of 3.5 and 8.8 ppbv, respectively. At most sites O3 was significantly correlated with fires in the surrounding 5 x 5 degrees and 10 x 10 degrees regions, but not with fires in the nearest 1 x 1 degree region, reflecting the balance between O3 production and destruction in a high NOx environment. BC was a slightly better predictor of O3, compared with BA. The relationship between O3 and temperature was examined at two sites (Yellowstone and Rocky Mountain National Parks). At these two sites, high fire years were significantly warmer than lowfire years; however, daytime seasonal meantemperature and O3 were not significantly correlated. This indicates that the presence of fire is a more important predictor for O3 than is temperature.