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Background: Since the outbreak of COVID-19, how to reduce the risk of spreading viruses and other microorganisms while performing aerosolgenerating procedures (AGPs) has become a challenging question within the dental and dental hygiene communities. The purpose of this position paper is to summarize the evidence of the effectiveness of various mitigation methods used to reduce the risk of infection transmission during AGPs in dentistry., Methods: The authors searched 6 databases-MEDLINE, EMBASE, Scopus, Web of Science, Cochrane Library, and Google Scholar-for relevant scientific evidence published between January 2012 and December 2022 to answer 6 research questions about the risk of transmission, methods, devices, and personal protective equipment (PPE) used to reduce contact with microbial pathogens and limit the spread of aerosols., Results: A total of 78 studies fulfilled the eligibility criteria. The literature on the risk of infection transmission including SARS-CoV-2 between dental hygienists and their patients is limited. Although several mouthrinses are effective in reducing bacterial contaminations in aerosols, their effectiveness against SARS-CoV-2 is also limited. The combined use of eyewear, masks, and face shields is effective in preventing contamination of the facial and nasal region while performing AGPs. High-volume evacuation with or without an intraoral suction, low-volume evacuation, saliva ejector, and rubber dam (when appropriate) have shown effectiveness in reducing aerosol transmission beyond the generation site. Finally, the appropriate combination of ventilation and filtration in dental operatories is effective in limiting the spread of aerosols., Discussion and Conclusion: Aerosols produced during clinical procedures can pose a risk of infection transmission between dental hygienists and their patients. The implementation of practices supported by available evidence will ensure greater patient and provider safety in oral health settings. More studies in oral health clinical environments would shape future practices and protocols, ultimately to ensure the delivery of safe clinical care., Competing Interests: The authors have no conflicts of interest to declare., (Copyright © 2024 American Dental Hygienists' Association and the Canadian Dental Hygienists Association.)

Background Since the outbreak of COVID-19, how to reduce the risk of spreading viruses and other microorganisms while performing aerosol generating procedures (AGPs) has become a challenging question within the dental and dental hygiene communities. The purpose of this position paper is to summarize the existing evidence about the effectiveness of various mitigation methods used to reduce the risk of infection transmission during AGPs in dentistry. Methods The authors searched six databases, MEDLINE, EMBASE, Scopus, Web of Science, Cochrane Library, and Google Scholar, for relevant scientific evidence published in the last ten years (January 2012 to December 2022) to answer six research questions about the the aspects of risk of transmission, methods, devices, and personal protective equipment (PPE) used to reduce contact with microbial pathogens and limit the spread of aerosols. Results A total of 78 studies fulfilled the eligibility criteria. There was limited literature to indicate the risk of infection transmission of SARS-CoV-2 between dental hygienists and their patients. A number of mouthrinses are effective in reducing bacterial contaminations in aerosols; however, their effectiveness against SARS-CoV-2 was limited. The combined use of eyewear, masks, and face shields are effective for the prevention of contamination of the facial and nasal region, while performing AGPs. High volume evacuation with or without an intraoral suction, low volume evacuation, saliva ejector, and rubber dam (when appropriate) have shown effectiveness in reducing aerosol transmission beyond the generation site. Finally, the appropriate combination of ventilation and filtration in dental operatories are effective in limiting the spread of aerosols. Conclusion Aerosols produced during clinical procedures can potentially pose a risk of infection transmission between dental hygienists and their patients. The implementation of practices supported by available evidence are best practices to ensure patient and provider safety in oral health settings. More studies in dental clinical environment would shape future practices and protocols, ultimately to ensure safe clinical care delivery., (Copyright © 2024 The American Dental Hygienists’ Association.)

The article focuses on a study which aims at developing a portable, autonomous aerosol lidar system. It discusses the challenges faced by Environment Canada in operating the national lidar network Canadian Operational Research Aerosol Lidar Network (CORALNet) and describes the aerosol lidar technique which is used for measuring backscattered photons from a pulsed laser source.

Below-cloud scavenging (BCS) is the process of aerosol removal from the atmosphere between cloud base and the ground by precipitation (e.g., rain or snow), and affects aerosol number or mass concentrations, size distribution, and lifetime. An accurate representation of precipitation phases is important in treating BCS as the efficiency of aerosol scavenging differs significantly between liquid and solid precipitation. The impact of different representations of BCS on existing model biases was examined through implementing a new aerosol BCS scheme in the Environment and Climate Change Canada (ECCC) air quality prediction model GEM-MACH and comparing it with the existing scavenging scheme in the model. Further, the current GEM-MACH employs a single-phase precipitation for BCS: total precipitation is treated as either liquid or solid depending on a fixed environment temperature threshold. Here, we consider co-existing liquid and solid precipitation phases as they are predicted by the GEM microphysics. GEM-MACH simulations, in a local-area domain over the Athabasca oil sands areas, Canada, are compared with observed precipitation samples, with a focus on the particulate base cation NH 4+ ; acidic anions NO 3- , SO 4= , HSO 3- in precipitation; and observed ambient particulate sulfate, ammonium, and nitrate concentrations. Overall, the introduction of the multi-phase approach and the new scavenging scheme enhances GEM-MACH performance compared to previous methods. Including a multi-phase approach leads to altered SO 4= scavenging and impacts the BCS of SO 2 into the aqueous phase over the domain. Sulfate biases improved from +46% to -5% relative to Alberta Precipitation Quality Monitoring Program wet sulfate observations. At Canadian Air and Precipitation Monitoring Network stations the biases became more negative, from -10% to -30% for the tests carried out here. These improvements contrast with prior annual average biases of +200% for SO 4= , indicating enhanced model performance. Improvements in model performance (via scores for correlation coefficient, normalized mean bias, and/or fractional number of model values within a factor of 2 of observations) could also be seen between the base case and the two simulations based on multi-phase partitioning for NO 3- , NH 4+ , and SO 4=. Whether or not these improvements corresponded to increases or decreases in NO 3- and NH 4+ wet deposition varied over the simulation region. The changes were episodic in nature – the most significant changes in wet deposition were likely at specific geographic locations and represent specific cloud precipitation events. The changes in wet scavenging resulted in a higher formation rate and larger concentrations of atmospheric particle sulfate. [ABSTRACT FROM AUTHOR]

This paper describes a method for speciation of Hg associated with airborne particulate matter. This method uses a mini-sampler for sample collection and analysis, thermal desorption for separating Hg species, and inductively coupled plasma mass spectrometry (ICP-MS) for identification and quantification of Hg. Coal fly ash spiked with different Hg compounds (e.g. Hg0, HgCl2, HgO, and HgS) was used for qualitative calibration. A standard reference material with a certified value for Hg concentration was used to evaluate the method. When the temperature of the furnace was programmed at a linear rate of increase of 50° min-1, different Hg compounds could clearly be separated. Three airborne particulate matter samples were collected in parallel in Toronto, ON, Canada and analyzed using this method. Reproducible results were obtained and Hg0, HgCl2, HgO, and HgS species from these samples were detected. [ABSTRACT FROM AUTHOR]

This paper is concerned with uncertainties in the Advanced Very High Resolution Radiometer (AVHRR)-based retrieval of optical depth for heavy smoke aerosol plumes generated from forest fires that occurred in Canada due to a lack of knowledge on their optical properties (single-scattering albedo and asymmetry parameter). Typical values of the optical properties for smoke aerosols derived from such field experiments as Smoke, Clouds, and Radiation-Brazil (SCAR-B); Transport and Atmospheric Chemistry near the Equator-Atlantic (TRACE-A); Biomass Burning Airborne and Spaceborne Experiment in the Amazonas (BASE-A); and Boreal Ecosystem–Atmosphere Study (BOREAS) were first assumed for retrieving smoke optical depths. It is found that the maximum top-of-atmosphere (TOA) reflectance values calculated by models with these aerosol parameters are less than observations whose values are considerably higher. A successful retrieval would require an aerosol model that either has a substantially smaller asymmetry parameter (g < 0.4 versus g > 0.5), or higher single-scattering albedo (ω ≫ 0.9 versus ω < 0.9), or both (e.g., g = 0.39 and ω = 0.91 versus g = 0.57 and ω = 0.87) than the existing models. Several potential causes were examined including small smoke particle size, low black carbon content, humidity effect, calibration errors, inaccurate surface albedo, mixture of cloud and aerosol layers, etc. A more sound smoke aerosol model is proposed that has a lower content of black carbon (mass ratio = 0.015) and smaller size (mean radius = 0.02 μm for dry smoke particles), together with consideration of the effect of relative humidity. Ground-based observations of smoke suggest that for τ < 2.5 there is an increasing trend in ω and a decreasing trend in g with increases in τ, which is consistent with the results of satellite retrievals. Using these relationships as constraints, more plausible values of τ can b... [ABSTRACT FROM AUTHOR]

Due to a lack of high-latitude ground-based and satellite-based data from traditional passive- and active-based measurements, the impact of aerosol particles on the Arctic region is one of the least understood factors contributing to recent Arctic sea ice changes. In this study, we investigated the feasibility of using the ultraviolet (UV) aerosol index (AI) parameter from the Ozone Monitoring Instrument (OMI), a semi-quantitative aerosol parameter, for quantifying spatiotemporal changes in UV-absorbing aerosols over the Arctic region. We found that OMI AI data are affected by an additional row anomaly that is unflagged by the OMI quality control flag and are systematically biased as functions of observing conditions, such as azimuth angle, and certain surface types over the Arctic region, resulting in an anomalous "ring" of climatologically high AI centered at about 70 ∘ N, surrounding an area of low AI over the pole. Two methods were developed in this study for quality-assuring the Arctic AI data. Using quality-controlled OMI AI data from 2005 through 2020, we found decreases in UV-absorbing aerosols in the spring months (April and May) over much of the Arctic region and increases in UV-absorbing aerosols in the summer months (June, July, and August) over northern Russia and northern Canada. Additionally, we found significant increases in the frequency and size of UV-absorbing aerosol events across the Arctic and high-Arctic (north of 80 ∘ N) regions for the latter half of the study period (2014–2020), driven primarily by a significant increase in boreal biomass-burning plume coverage. [ABSTRACT FROM AUTHOR]

Ice wedges are a characteristic ground ice feature in permafrost regions that form primarily from the meltwater of the seasonal snowpack. Ice‐wedge oxygen and hydrogen stable isotopes have been used in winter paleotemperature reconstructions; however, until recently, the ion geochemistry of ice wedges has rarely been analyzed as a potential paleoclimate proxy. This potential is greatest for ice wedges located in coastal regions, where marine aerosols are the dominant contributor to snowpack impurities. Here, we evaluate the source and integrity of ionic concentrations of a coastal ice wedge in the northwestern Canadian Arctic (Beaufort Sea coast) to evaluate the use of ice wedges as a marine aerosol archive. Comparison to a regionally comparable snowpack reveals remarkably similar ionic concentrations for Cl−, Na+, Br−, SO42−, Ca2+, and Mg2+, with a Cl−/Na+ ratio similar to bulk seawater (1.80 vs. 1.79 in seawater), suggesting that marine aerosols, probably from sea salt aerosol production during blowing snow events over sea ice as indicated by depleted SO42− values relative to Na+, are probably the dominant contributor to ion concentrations. A previously established linear age model for the ice wedge is used to develop a continuous ion record spanning ~4,600 to ~700 yr b2k. Cl− and Na+ concentrations reveal a strong and continuous increase in concentrations over the late Holocene, thought to be driven by reduced distance‐to‐coast of up to 1 km as a result of coastal erosion. This study presents a novel interpretation of ice‐wedge geochemical data and represents the first Holocene ice‐wedge ion record. [ABSTRACT FROM AUTHOR]

A major achievement in research supported by the Kluane Lake Research Station was the recovery, in 2001 - 02, of a suite of cores from the icefields of the central St. Elias Mountains, Yukon, by teams of researchers from Canada, the United States, and Japan. This project led to the development of parallel, long (10³ - 104 year) ice-core r ecords of climate and atmospheric change over an altitudinal range of more than 2 km, from the Eclipse Icefield (3017 m) to the ice-covered plateau of Mt. Logan (5340 m). These efforts built on earlier work recovering single ice cores in this region. Comparison of these records has allowed for variations in climate and atmospheric composition to be linked with changes in the vertical structure and dynamics of the North Pacific atmosphere, providing a unique perspective on these changes over the Holocene. Owing to their privileged location, cores from the St. Elias Icefields also contain a remarkably detailed record of aerosols from various sources around or across the North Pacific. In this paper we review major scientific findings from the study of St. Elias Mountain ice cores, focusing on five main themes: (1) The record of stable water isotopes (δ18O, δD), which has unique characteristics that differ from those of Greenland, other Arctic ice cores, and even among sites in the St. Elias; (2) the snow accumulation history; (3) the record of pollen, biomass burning aerosol, and desert dust deposition; (4) the record of long-range air pollutant deposition (sulphate and lead); and (5) the record of paleo-volcanism. Our discussion draws on studies published since 2000, but based on older ice cores from the St. Elias Mountains obtained in 1980 and 1996. [ABSTRACT FROM AUTHOR]

The photolysis module in Environment and Climate Change Canada's online chemical transport model GEM-MACH (GEM: Global Environmental Multi-scale – MACH: Modelling Air quality and Chemistry) was improved to make use of the online size and composition-resolved representation of atmospheric aerosols and relative humidity in GEM-MACH, to account for aerosol attenuation of radiation in the photolysis calculation. We coupled both the GEM-MACH aerosol module and the MESSy-JVAL (Modular Earth Submodel System) photolysis module, through the use of the online aerosol modeled data and a new Mie lookup table for the model-generated extinction efficiency, absorption and scattering cross sections of each aerosol type. The new algorithm applies a lensing correction factor to the black carbon absorption efficiency (core-shell parameterization) and calculates the scattering and absorption optical depth and asymmetry factor of black carbon, sea salt, dust and other internally mixed components. We carried out a series of simulations with the improved version of MESSy-JVAL and wildfire emission inputs from the Canadian Forest Fire Emissions Prediction System (CFFEPS) for 2 months, compared the model aerosol optical depth (AOD) output to the previous version of MESSy-JVAL, satellite data, ground-based measurements and reanalysis products, and evaluated the effects of AOD calculations and the interactive aerosol feedback on the performance of the GEM-MACH model. The comparison of the improved version of MESSy-JVAL with the previous version showed significant improvements in the model performance with the implementation of the new photolysis module and with adopting the online interactive aerosol concentrations in GEM-MACH. Incorporating these changes to the model resulted in an increase in the correlation coefficient from 0.17 to 0.37 between the GEM-MACH model AOD 1-month hourly output and AERONET (Aerosol Robotic Network) measurements across all the North American sites. Comparisons of the updated model AOD with AERONET measurements for selected Canadian urban and industrial sites, specifically, showed better correlation coefficients for urban AERONET sites and for stations located further south in the domain for both simulation periods (June and January 2018). The predicted monthly averaged AOD using the improved photolysis module followed the spatial patterns of MERRA-2 reanalysis (Modern-Era Retrospective analysis for Research and Applications – version 2), with an overall underprediction of AOD over the common domain for both seasons. Our study also suggests that the domain-wide impacts of direct and indirect effect aerosol feedbacks on the photolysis rates from meteorological changes are considerably greater (3 to 4 times) than the direct aerosol optical effect on the photolysis rate calculations. [ABSTRACT FROM AUTHOR]

Abstract: The Canadian National Air Pollution Surveillance (NAPS) network, monitoring criteria gases (CO, O3, NOx, and SO2), PM2.5, PM10, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs) and particle chemical mass and composition, has been in operation for over 40 years. Since 1984 both fine (<2.5 μm – PM2.5) and coarse (2.5–10 μm – PM10–2.5) particle mass measurements have been made at NAPS network sites using dichotomous samplers. In January 2003, the NAPS PM2.5 speciation program was initiated with the purpose of measuring all major components of PM2.5, including ammonium nitrate, ammonium sulphate, metals, and organic and elemental carbon. The present paper describes the improved sampling (e.g. Teflon/Nylon filter packs for nitrate loss, and an active blank for each and every sample in the determination of positive organic carbon artifacts), and analytical methods used in the Canadian NAPS PM2.5 speciation program. A detailed dataset was then analyzed for seasonal and geographical variations in the major components of 24-h time integrated PM2.5 samples collected at eight urban and three rural measurement sites across Canada (2003–2008). Chemical mass reconstruction was used for assessment of the adequacy of selected sampling and chemical parameters as well as for the determination of the relative contributions of different compound classes to PM2.5 mass. The highest frequency of PM2.5 episodes exceeding 30 μg m−3 were observed in Ontario and southern Quebec. In general, the most important contributions to PM2.5 mass were secondary aerosol sulphate and nitrate (38–63% for western sites and 3–44% for eastern sites), depending on the season. Organic matter (OM) was found to be the second most important component (21–45%), while particle-bound water (PBW) accounted for 6–12% of the PM2.5 mass. Golden B.C. was an exception, exhibiting high levels of OM (60–70%) and low levels of PBW (∼3%). [Copyright &y& Elsevier]

The chemical composition, sources, and concentrations of aerosol particles vary on a seasonal basis in the Arctic. While existing research has focused on understanding the occurrence of aerosol particles during the Arctic winter and spring, less is known of their occurrence during the Arctic summer. In this study, atmospheric aerosol particle chemical composition and concentration were determined during July–September 2018 at Tuktoyaktuk, NT, Canada (69.4 ∘ N, 133.0 ∘ W), to coincide with the Year of Polar Prediction's Second Special Observing Period in the Arctic. The chemical composition of fine (PM 2.5) and coarse (PM 10–2.5) aerosol filter samples suggests the ocean, mineral and/or road dust, and combustion were sources of the sampled aerosol particles. Mass concentrations of PM 2 and PM 10 , estimated from optical particle counter measurements, remained within a similar range during the study. However, elevated mass concentrations coincided with a festival in the community of Tuktoyaktuk, suggesting local human activity was an important source of aerosol particles. Mass concentrations of PM 2 , which promote negative health effects in humans, were significantly lower at Tuktoyaktuk than the national air quality standard recommended by the government of Canada. These measurements provide an important baseline to compare with future measurements associated with the assessment of aerosol chemistry and air quality in the Arctic. [ABSTRACT FROM AUTHOR]

3,3′-dichlorobiphenyl (IUPAC No. 11), a chlorobiphenyl (CB) that is not generally analysed in environmental studies of CBs, is found, sometimes at high concentrations, in water, suspended particulate material, biota and sediments from Halifax Harbour, NS, Canada. The results presented demonstrate the need for investigations of non-Aroclor CBs like CB 11. Not only can they have rather elevated environmental concentrations like those reported here for CB 11, but they also can be members of the more toxic non-ortho class of CBs and thus important from a toxicity standpoint. The focus of this paper was to investigate the possible sources of CB 11, a trace constituent of commercial mixtures, but dominant in various environmental compartments of Halifax Harbour. [Copyright &y& Elsevier]

We present an algorithm for retrieving aerosol layer height (ALH) and aerosol optical depth (AOD) for smoke over vegetated land and water surfaces from measurements of the Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR). The algorithm uses Earth-reflected radiances in six EPIC bands in the visible and near-infrared and incorporates flexible spectral fitting that accounts for the specifics of land and water surface reflectivity. The fitting procedure first determines AOD using EPIC atmospheric window bands (443, 551, 680, and 780 nm), then uses oxygen (O2) A and B bands (688 and 764 nm) to derive ALH, which represents an optical centroid altitude. ALH retrieval over vegetated surface primarily takes advantage of measurements in the O2 B band. We applied the algorithm to EPIC observations of several biomass burning events over the United States and Canada in August 2017. We found that the algorithm can be used to obtain AOD and ALH multiple times daily over water and vegetated land surface. Validation is performed against aerosol extinction profiles detected by the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) and against AOD observed at nine Aerosol Robotic Network (AERONET) sites, showing, on average, an error of 0.58 km and a bias of -0.13 km in retrieved ALH and an error of 0.05 and a bias of 0.03 in retrieved AOD. Additionally, we show that the aerosol height information retrieved by the present algorithm can potentially benefit the retrieval of aerosol properties from EPIC's ultraviolet (UV) bands. [ABSTRACT FROM AUTHOR]

In mid-August through mid-September of 2017 a major wildfire smoke and haze episode strongly impacted most of the NW US and SW Canada. During this period our ground-based site in Missoula, Montana, experienced heavy smoke impacts for ∼500 h (up to 471 µ g m -3 hourly average PM 2.5). We measured wildfire trace gases, PM 2.5 (particulate matter ≤2.5 µ m in diameter), and black carbon and submicron aerosol scattering and absorption at 870 and 401 nm. This may be the most extensive real-time data for these wildfire smoke properties to date. Our range of trace gas ratios for ΔNH3/ΔCO and ΔC2H4/ΔCO confirmed that the smoke from mixed, multiple sources varied in age from ∼2 –3 h to ∼1 –2 days. Our study-average ΔCH4/ΔCO ratio (0.166±0.088) indicated a large contribution to the regional burden from inefficient smoldering combustion. Our ΔBC/ΔCO ratio (0.0012±0.0005) for our ground site was moderately lower than observed in aircraft studies (∼0.0015) to date, also consistent with a relatively larger contribution from smoldering combustion. Our ΔBC/ΔPM2.5 ratio (0.0095±0.0003) was consistent with the overwhelmingly non-BC (black carbon), mostly organic nature of the smoke observed in airborne studies of wildfire smoke to date. Smoldering combustion is usually associated with enhanced PM emissions, but our ΔPM2.5/ΔCO ratio (0.126±0.002) was about half the ΔPM1.0/ΔCO measured in fresh wildfire smoke from aircraft (∼0.266). Assuming PM 2.5 is dominated by PM 1 , this suggests that aerosol evaporation, at least near the surface, can often reduce PM loading and its atmospheric/air-quality impacts on the timescale of several days. Much of the smoke was emitted late in the day, suggesting that nighttime processing would be important in the early evolution of smoke. The diurnal trends show brown carbon (BrC), PM 2.5 , and CO peaking in the early morning and BC peaking in the early evening. Over the course of 1 month, the average single scattering albedo for individual smoke peaks at 870 nm increased from ∼0.9 to ∼0.96. Bscat401/Bscat870 was used as a proxy for the size and "photochemical age" of the smoke particles, with this interpretation being supported by the simultaneously observed ratios of reactive trace gases to CO. The size and age proxy implied that the Ångström absorption exponent decreased significantly after about 10 h of daytime smoke aging, consistent with the only airborne measurement of the BrC lifetime in an isolated plume. However, our results clearly show that non-BC absorption can be important in "typical" regional haze and moderately aged smoke, with BrC ostensibly accounting for about half the absorption at 401 nm on average for our entire data set. [ABSTRACT FROM AUTHOR]

Modelling studies suggest that the climate and the hydrological cycle are sensitive to the concentrations of ice-nucleating particles (INPs). However, the concentrations, composition, and sources of INPs in the atmosphere remain uncertain. Here, we report daily concentrations of INPs in the immersion freezing mode and tracers of mineral dust (Al, Fe, Ti, and Mn), sea spray aerosol (Na+ and Cl-), and anthropogenic aerosol (Zn, Pb, NO3- , NH4+ , and non-sea-salt SO42-) at Alert, Canada, during a 3-week campaign in March 2016. In total, 16 daily measurements of INPs are reported. The average INP concentrations measured in the immersion freezing mode were 0.005±0.002 , 0.020±0.004 , and 0.186±0.040 L -1 at -15 , -20 , and -25 ∘ C, respectively. These concentrations are within the range of concentrations measured previously in the Arctic at ground level or sea level. Mineral dust tracers all correlated with INPs at -25 ∘ C (correlation coefficient, R , ranged from 0.70 to 0.76), suggesting that mineral dust was a major contributor to the INP population at -25 ∘ C. Particle dispersion modelling suggests that the source of the mineral dust may have been long-range transport from the Gobi Desert. Sea spray tracers were anti-correlated with INPs at -25 ∘ C (R=-0.56). In addition, INP concentrations at -25 ∘ C divided by mass concentrations of aluminum were anti-correlated with sea spray tracers (R=-0.51 and -0.55 for Na+ and Cl- , respectively), suggesting that the components of sea spray aerosol suppressed the ice-nucleating ability of mineral dust in the immersion freezing mode. Correlations between INPs and anthropogenic aerosol tracers were not statistically significant. These results will improve our understanding of INPs in the Arctic during spring. [ABSTRACT FROM AUTHOR]

Simple Summary: This study aims to quantify the effects of smoke originating from boreal biomass-burning fires on solar radiation propagating through the atmosphere. The wildfires that took place in summer 2017 along Greenland's west coast and northern Canada produced a considerable amount of particles that were transported north and northeast, respectively, and were detected at the Thule High Arctic Atmospheric Observatory (THAAO; 76.53 ∘ N, 68.74 ∘ W). Solar radiation measurements carried out at THAAO, satellite data, and modeled radiations allowed the estimation of surface cooling and the warming aloft at two atmospheric layers (at altitudes of approximately 5 and 11 km asl) due to the presence of the biomass-burning aerosol particles. Boreal fires have increased during the last years and are projected to become more intense and frequent as a consequence of climate change. Wildfires produce a wide range of effects on the Arctic climate and ecosystem, and understanding these effects is crucial for predicting the future evolution of the Arctic region. This study focuses on the impact of the long-range transport of biomass-burning aerosol into the atmosphere and the corresponding radiative perturbation in the shortwave frequency range. As a case study, we investigate an intense biomass-burning (BB) event which took place in summer 2017 in Canada and subsequent northeastward transport of gases and particles in the plume leading to exceptionally high values (0.86) of Aerosol Optical Depth (AOD) at 500 nm measured in northwestern Greenland on 21 August 2017. This work characterizes the BB plume measured at the Thule High Arctic Atmospheric Observatory (THAAO; 76.53 ∘ N, 68.74 ∘ W) in August 2017 by assessing the associated shortwave aerosol direct radiative impact over the THAAO and extending this evaluation over the broader region ( 60 ∘ N– 80 ∘ N, 110 ∘ W– 0 ∘ E). The radiative transfer simulations with MODTRAN6.0 estimated an aerosol heating rate of up to 0.5 K/day in the upper aerosol layer (8–12 km). The direct aerosol radiative effect (ARE) vertical profile shows a maximum negative value of −45.4 Wm − 2 for a 78 ∘ solar zenith angle above THAAO at 3 km altitude. A cumulative surface ARE of −127.5 TW is estimated to have occurred on 21 August 2017 over a portion (∼ 3.1 × 10 6 km 2 ) of the considered domain ( 60 ∘ N– 80 ∘ N, 110 ∘ W– 0 ∘ E). ARE regional mean daily values over the same portion of the domain vary between −65 and −25 Wm − 2 . Although this is a limited temporal event, this effect can have significant influence on the Arctic radiative budget, especially in the anticipated scenario of increasing wildfires. [ABSTRACT FROM AUTHOR]

High time-resolved aircraft data, concurrent surface measurements and air quality model simulations were explored to diagnose the processes influencing aerosol chemistry under the influence of lake-breeze circulations in a polluted region of southwestern Ontario, Canada. The analysis was based upon horizontal aircraft transects conducted at multiple altitudes across an entire lake-breeze circulation. Air mass boundaries due to lake-breeze fronts were identified in the aircraft meteorological and chemical data, which were consistent with the frontal locations determined from surface analyses. Observations and modelling support the interpretation of a lake-breeze circulation where pollutants were lofted at a lake-breeze front, transported in the synoptic flow, caught in a downdraft over the lake, and then confined by onshore flow. The detailed analysis led to the development of conceptual models that summarize the complex 3-D circulation patterns and their interaction with the synoptic flow. The identified air mass boundaries, the interpretation of the lake-breeze circulation, and the air parcel circulation time in the lake-breeze circulation (3.0 to 5.0 h) enabled formation rates of organic aerosol (OA/ΔCO) and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed to be determined. The formation rate for OA (relative to excess CO in ppmv) was found to be 11.6-19.4 µgm-3 ppmv-1 h-1 and the Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed formation rate was 5.0-8.8 %h-1. The formation rates are enhanced relative to regional background rates implying that lake-breeze circulations are an important dynamic in the formation of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed and secondary organic aerosol. The presence of cumulus clouds associated with the lake-breeze fronts suggests that these enhancements could be due to cloud processes. Additionally, the effective confinement of pollutants along the shoreline may have limited pollutant dilution leading to elevated oxidant concentrations. [ABSTRACT FROM AUTHOR]

We describe aerosol optical depth (AOD) measured during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) experiment, focusing on vertical profiles, inter-comparison with correlative observations and fine-mode fraction. Arctic haze observed in <2 km and 2-4 km over Alaska in April 2008 originated mainly from anthropogenic emission and biomass burning, respectively, according to aerosol mass spectrometry and black carbon incandescence measurements. The Angstrom exponent for these air masses is 1.4 ± 0.3 and 1.7 ± 0.1, respectively, when derived at 499 nm from a second-order polynomial fit to the AOD spectra measured with the 14-channel Ames Airborne Tracking Sunphotometer (AATS-14) over 354-2139 nm. We examine 55 vertical profiles selected from all phases of the experiment. For two thirds of them, the AOD spectra are within 3% + 0.02 of the vertical integral of local visible-light scattering and absorption. The horizontal structure of smoke plumes from local biomass burning observed in central Canada in June and July 2008 explains most outliers. The differences in mid-visible Angstrom exponent are <0.10 for 63% of the profiles with 499-nm AOD > 0.1. The retrieved fine-mode fraction of AOD is mostly between 0.7 and 1.0, and its root mean square difference (in both directions) from column-integral submicron fraction (measured with nephelometers, absorption photometers and an impactor) is 0.12. These AOD measurements from the NASA P-3 aircraft, after compensation for below-aircraft light attenuation by vertical extrapolation, mostly fall within ± 0.02 of AERONET ground-based measurements between 340-1640 nm for five overpass events. [ABSTRACT FROM AUTHOR]

The article discusses ultraviolet (UV)-B cloud optical properties for Canada. It discusses the importance of cloud optical properties on the amount of UV-B irradiance reaching the ground. It also discusses the use of discrete ordinate radiative transfer (DISORT) and delta-Eddington algorithms in overcast cloud optical depth estimation.

Threats associated with bioaerosol weapons have been around for several decades. However, with the recent political developments that changed the image and dynamics of the international order and security, the visibility and importance of these bioaerosol threats have considerably increased. Over the last few years, Defence Research and Development Canada has investigated the spectrometric LIDAR-based standoff bioaerosol detection technique to address this menace. This technique has the advantages of rapidly monitoring the atmosphere over wide areas without physical intrusions and reporting an approaching threat before it reaches sensitive sites. However, it has the disadvantages of providing a quality of information that degrades as a function of range and bioaerosol concentration. In order to determine the importance of these disadvantages, Canada initiated in 1999 the SINBAHD (Standoff Integrated Bioaerosol Active Hyperspectral Detection) project investigating the standoff detection and characterization of threatening biological clouds by Laser-Induced Fluorescence (LIF) and intensified range-gated spectrometric detection techniques. This article reports an overview of the different lessons learned with this program. Finally, the BioSense project, a Technology Demonstration Program aiming at the next generation of wide area standoff bioaerosol sensing, mapping, tracking and classifying systems, is introduced. [ABSTRACT FROM AUTHOR]

Because the health effects of manganese are dependent its oxidation-state, we have improved upon oxidation-state resolved methods to quantify soluble manganese in atmospheric aerosols. Two spectrophotometric methods were adapted for measurements in atmospheric aerosols in order to measure total soluble manganese (Mnsol) and soluble oxidized manganese [Mn(III) and Mn(IV), Mnox]. Using the formaldoxime method, we noted a detection limit two orders of magnitude better than past studies using trace-metal clean techniques and a 1 meter path-length spectrophotometric cell. Extractions of co-located aerosol samples were performed in four environmentally or biologically relevant extract solutions and processed for soluble manganese analysis. The quantity of manganese extracted was a strong function of the fluid, and the greatest amount of manganese was extracted in the rain-water surrogate (acetate buffered solution). Mnsol in East St. Louis, IL, USA (6-20% of the total manganese) was less than the Mnsol in aerosols collected in Toronto, ON, Canada (40% of the total). Mnox was not detected in the PM10 samples collected in East St. Louis, however Mnox accounted for around 30% of the PM2.5 soluble manganese in Toronto. Mnox was not detected in the coarse fraction in Toronto, which may imply that soils are not a source of Mnox at this site. Oxidized manganese was not recoverable from extracts of samples from East St. Louis spiked with 1 μg Mnox L-1. This implies that a soluble component of the aerosol is responsible for reduction of oxidized manganese and that the chemical form of manganese in aerosols can quickly change when it comes into contact with a fluid. [ABSTRACT FROM AUTHOR]

Simultaneous ACE (Atmospheric Chemistry Experiment) upper tropospheric CO, C2H6, HCN, CH3Cl, CH4, C2H2, CH3OH, HCOOH, and OCS measurements show plumes up to 185 ppbv (10-9 per unit volume) for CO, 1.36 ppbv for C2H6, 755 pptv (10-12 per unit volume) for HCN, 1.12 ppbv for CH3Cl, 1.82 ppmv (10-6 per unit volume) for CH4, 0.178 ppbv for C2H2, 3.89 ppbv for CH3OH, 0.843 ppbv for HCOOH, and 0.48 ppbv for OCS in western Canada and Alaska at 50°N-68°N latitude between 29 June and 23 July 2004. Enhancement ratios and emission factors for HCOOH, CH3OH, HCN, C2H6, and OCS relative to CO at 250-350 hPa are inferred from measurements of young plumes compared with lower mixing ratios assumed to represent background conditions based on a CO emission factor derived from boreal measurements. Results are generally consistent with the limited data reported for various vegetative types and emission phases measured in extratropical forests including boreal forests. The low correlation between fire product emission mixing ratios and the SF6 mixing ratio is consistent with no significant SF6 emissions from the biomass fires. [ABSTRACT FROM AUTHOR]

During the New England Air Quality Study (NEAQS) in the summer of 2004, airborne measurements were made of the major inorganic ions and the water-soluble organic carbon (WSOC) of the submicron (PM1.0) aerosol. These and ancillary data are used to describe the overall aerosol chemical characteristics encountered during the study. Fine particle mass was estimated from particle volume and a calculated density based on measured particle composition. Fine particle organic matter (OM) was estimated from WSOC and a mass balance analysis. The aerosol over the northeastern United States (U.S.) and Canada was predominantly sulfate and associated ammonium, and organic components, although in unique plumes additional ionic components were also periodically above detection limits. In power generation regions, and especially in the Ohio River Valley region, the aerosol tended to be predominantly sulfate (~ 60%µgµg-1) and apparently acidic, based on an excess of measured anions compared to cations. In all other regions where sulfate concentrations were lower and a smaller fraction of overall mass, the cations and anions were balanced suggesting a more neutral aerosol. In contrast, the WSOC and estimated OM were more spatially uniform and the fraction of OM relative to PM mass was largely influenced by sources of sulfate. The study median OM mass fraction was 40%. Throughout the study region, sulfate and organic aerosol mass were highest near the surface and decreased rapidly with increasing altitude. The relative fraction of organic mass to sulfate was similar throughout all altitudes within the boundary layer (altitude less than 2.5 km), but was significantly higher at altitude layers in the free troposphere (above 2.5 km). A number of distinct biomass burning plumes from fires in Alaska and the Yukon were periodically intercepted, mostly at altitudes between 3 and 4 km. These plumes were associated with highest aerosol concentrations of the study and were largely comprised of organic aerosol components (~60%). [ABSTRACT FROM AUTHOR]

Airborne in situ measurements of vertical profiles and horizontal transects of aerosol optical and physical properties, obtained during the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) field campaign off the East Coast of the United States during the summer of 2001, are presented. Most of the measurements were obtained in relatively clean air dominated by airflows that had passed over Canada and the northern Atlantic Ocean. Results from the 17 July and 2 August 2001 flights are presented; on these days, the aerosol loading was relatively high. In the lower troposphere, ω0 values at a wavelength of 550 nm were consistently above 0.93 throughout the field experiment, indicating the dominance of weakly absorbing aerosol. Particle number size distributions are presented and discussed for transects at altitudes ∼0.05–3.5 km above mean sea level. Particles with diameters (Dp) <0.1 μm made up the majority of the aerosol number. Accumulation mode particles dominate the number size, surface area, and volume distributions. The variability of optical and physical aerosol parameters was analyzed on horizontal scales of ∼1–4 km. There was little horizontal variability in the single-scattering albedo (ω0), aerosol optical depth (AOD), and accumulation mode size, but greater variability in particle number concentration. Comparisons of the airborne measurements with remotely sensed aerosol parameters, such as ω0 and effective particle radius (reff), derived from the Multiangle Imaging Spectroradiometer (MISR) aboard the Terra satellite were generally in good agreement. Overall, the MISR retrievals captured both the similarities and the differences between the properties of the aerosols measured on 17 July and 2 August. [ABSTRACT FROM AUTHOR]

A complete set of Advanced Very High Resolution Radiometer (AVHRR) data (75 images) is used to retrieve aerosol optical depth (AOD) over dense vegetation and over lake water in the visible AVHRR channel. The present approach for remote sensing of aerosols from the National Oceanic and Atmospheric Administration (NOAA)-11 AVHRR sensor is based on the detection of atmospherically dominated signals over dark surface covers such as dense dark vegetation (DDV). Such targets were identified using the reflective portion of the middle-wave AVHRR channel 3 signal. When a fixed DDV surface reflectance is subtracted from the observed reflectance after correction for all other atmospheric effects, the remaining part, which is due to aerosols, is inverted to derive aerosol optical thickness using a look-up table (LUT) similar to that used in water surface inversion. The algorithm was applied to the daily afternoon NOAA-11 AVHRR (1 km×1 km) data acquired from the end of May to mid-August 1994 over the Canadian 1000 km×1000 km Boreal Ecosystem Atmosphere Study (BOREAS) domain. A validation analysis using five ground-based Sun photometers within the studied area shows the good performance of the retrieval algorithm. The approach allows detailed analysis of the AOD spatio-temporal behaviour at the regional scale useful for climate and transport model validation. [ABSTRACT FROM AUTHOR]