Transport and transformation of atmospheric aerosol across Central Europe with emphasis on anthropogenic sources

<p>The trend in PM<sub>10</sub> concentrations in Europe has stagnated over the last two decades, showing only limited annual changes even though there are continued reductions in PM emissions. Possible reasons could be linked to both the aging processes of the particles in the atmosphere and their long-range transport. Therefore, better understanding the multiple origins of the atmospheric aerosol, their sources apportionment at different places are necessary for the development of efficient mitigation strategies. The ultimate objective of the project TRACE is to assess the transport and transformation of atmospheric aerosol across Central Europe with emphasis on anthropogenic sources (including coal and wood combustion) using synergic measurement methods (offline and online) and state-of-the art modelling tools including receptor-oriented models and Chemical transport models. Measurements were performed during winter and summer periods in 2021 simultaneously at three sampling places (Melpitz, DE, Kosetice, CZ, and Frydland, CZ) using state-of-the-art online and offline comprehensive chemical characterization of the atmospheric aerosol. Preliminary results from Scanning Mobility Particle Sizer (SMPS) showed peaks as high as 50 µg/m³ mass concentration during a dust event. Moreover, results from Aerosol Mass Spectrometer (AMS) and receptor modeling (RF) via Positive Matrix Factorization (PMF) from the winter campaign will be presented. </p>

The importance of termites and fire to dead wood consumption in the longleaf pine ecosystem

Microbes, insects, and fire are the primary drivers of wood loss from most ecosystems, but interactions among these factors remain poorly understood. In this study, we tested the hypothesis that termites and fire have a synergistic effect on wood loss from the fire-adapted longleaf pine (Pinus palustris Mill.) ecosystem in the southeastern United States. We predicted that the extensive galleries created by termites would promote the ignition and consumption of logs by fire. We exposed logs from which termites had or had not been excluded to prescribed fire after 2.5 years in the field. We found little support for our hypothesis as there was no significant interactive effect of termites and fire on wood mass loss. Moreover, there was no significant difference in mass loss between burned and unburned logs. Termites were responsible for about 13.3% of observed mass loss in unprotected logs, a significant effect, while microbial activity accounted for most of the remaining mass loss. We conclude that fire has little effect on wood loss from the longleaf pine ecosystem and that termite activity does not strongly promote wood combustion. However, longer term research involving multiple burn cycles, later stages of decay, and differing fire intensities will be needed to fully address this question.

Investigating the concentration levels, distribution patterns, source identification and health risk assessment of PAHs, n-alkanes, hopanes, and steranes in deposited dust of Mashhad, Iran

Deposited dust (DD) in urban environments contains carcinogenic organic compounds. The Indoor air quality is greatly affected by heating, ventilation, and air conditioning systems (HVAC), and in the Middle East most of the buildings are equipped by HVAC on top of them. It is possible that the DD on the roof near this equipment would be transferred to an indoor area. For these reasons, 40 samples of the over the roof DD were prepared, and organic compounds (16PAH compounds, 20n-alkane homologs, 8hopanes, and 6steranes) of DD were extracted using Soxhlet and analyzed by GC-MS. Source identification of organic compounds conducted by ring classification, diagnostic ratios, and factor analysis (FA). The results showed that the average (±SD) of total PAHs, n-alkanes, hopanes and steranes in DD were 1356.00 (±291.45) ng kg−1dw, 3211.65 (±969.18), 146.37 (±79.45) and 469.76 (±188.25) µg.g_1dw, respectively. The highest concentration of organic compounds was in the city center, where traffic congestion is common. Diagnostic ratios of n-alkanes results showed the dominant source is vehicular emission. FA results indicated vehicular emission and biogenic sources. In agreement, the results of sterane and hopane profiles confirm these results. On the other hand, the PAHs diagnostic ratios results indicated petroleum combustion sources. In this regard, FA findings showed combustion from vehicular emission and natural gas and wood combustion were the main factors. Furthermore, the incremental lifetime cancer risk was calculated as 8.45× 10−12 for children and 9.80 × 10−7 for adults, and the imposed risk was negligible.

Air Particulate Matter in Pollluted New Zealand Urban Environments: Sources, Patterns and Transport

<p>During the winters of 2010 and 2011, three intensive particulate matter (PM) monitoring campaigns were undertaken in Masterton, Alexandra and Nelson, New Zealand. The goal of these campaigns was, for the first time, to identify the sources and factors contributing to elevated PM concentrations on an hourly time-scale. In each location, hourly coarse (PM₁₀-₂.₅; particles with aerodynamic diameters 2.5 μm < d < 10 μm) and fine (PM₂.₅; particles with aerodynamic diameters < 2.5 μm) samples, PM₁₀ (particles with aerodynamic diameters < 10 μm, incorporating the coarse and fine fractions) concentrations and meteorological variables were collected from a number of sites. Using elemental concentrations determined from ion beam analysis and black carbon concentrations determined from light reflection for each hourly sample, PM sources and their contributions on an hourly time-scale were identified using positive matrix factorization (PMF). In Masterton, where two sampling sites were employed, PM₁₀ concentrations displayed distinct diurnal cycles, with peak concentrations occurring in the evening (7 pm–midnight) and in the morning (7–9 am). Four PM sources were identified (biomass burning, marine aerosol, crustal matter and vehicles) at each of the sites and biomass burning was identified as the most dominant source of PM₁₀ during both the evening and morning. One of the sites experienced consistently higher PM₁₀ concentrations and katabatic flows across Masterton were identified to be the main contributor to this phenomenon. In Alexandra and Nelson, three sampling sites on a horizontal transect (upwind, central and downwind of the general katabatic flow pathway) and a fourth site located centrally, but at a height of 26 m, were incorporated in a novel study design. Each of the sites in Alexandra and Nelson also showed diurnal patterns in PM₁₀ concentrations. The central site in Alexandra experienced consistently higher PM₁₀ concentrations and four PM₁₀ sources were identified at each of the sites (biomass burning, marine aerosol, vehicles and crustal matter). Biomass burning was identified as the main source of PM₁₀ throughout the day at each of the sites. The convergence of numerous katabatic flows was identified as the contributing factor to the elevated PM₁₀ concentrations measured at the central site. In Nelson, five PM sources were identified at each of the sites (biomass burning, vehicles, marine aerosol, shipping sulfate and crustal matter) and biomass burning was identified as the dominant source of PM₁₀ throughout the day. Katabatic flows were also identified to play an important role in PM₁₀ transport. Analyses of source-specific (wood combustion and vehicles) PM samples was also undertaken, and the results of these analyses are included in this thesis.</p>

Air Particulate Matter in Pollluted New Zealand Urban Environments: Sources, Patterns and Transport

<p>During the winters of 2010 and 2011, three intensive particulate matter (PM) monitoring campaigns were undertaken in Masterton, Alexandra and Nelson, New Zealand. The goal of these campaigns was, for the first time, to identify the sources and factors contributing to elevated PM concentrations on an hourly time-scale. In each location, hourly coarse (PM₁₀-₂.₅; particles with aerodynamic diameters 2.5 μm < d < 10 μm) and fine (PM₂.₅; particles with aerodynamic diameters < 2.5 μm) samples, PM₁₀ (particles with aerodynamic diameters < 10 μm, incorporating the coarse and fine fractions) concentrations and meteorological variables were collected from a number of sites. Using elemental concentrations determined from ion beam analysis and black carbon concentrations determined from light reflection for each hourly sample, PM sources and their contributions on an hourly time-scale were identified using positive matrix factorization (PMF). In Masterton, where two sampling sites were employed, PM₁₀ concentrations displayed distinct diurnal cycles, with peak concentrations occurring in the evening (7 pm–midnight) and in the morning (7–9 am). Four PM sources were identified (biomass burning, marine aerosol, crustal matter and vehicles) at each of the sites and biomass burning was identified as the most dominant source of PM₁₀ during both the evening and morning. One of the sites experienced consistently higher PM₁₀ concentrations and katabatic flows across Masterton were identified to be the main contributor to this phenomenon. In Alexandra and Nelson, three sampling sites on a horizontal transect (upwind, central and downwind of the general katabatic flow pathway) and a fourth site located centrally, but at a height of 26 m, were incorporated in a novel study design. Each of the sites in Alexandra and Nelson also showed diurnal patterns in PM₁₀ concentrations. The central site in Alexandra experienced consistently higher PM₁₀ concentrations and four PM₁₀ sources were identified at each of the sites (biomass burning, marine aerosol, vehicles and crustal matter). Biomass burning was identified as the main source of PM₁₀ throughout the day at each of the sites. The convergence of numerous katabatic flows was identified as the contributing factor to the elevated PM₁₀ concentrations measured at the central site. In Nelson, five PM sources were identified at each of the sites (biomass burning, vehicles, marine aerosol, shipping sulfate and crustal matter) and biomass burning was identified as the dominant source of PM₁₀ throughout the day. Katabatic flows were also identified to play an important role in PM₁₀ transport. Analyses of source-specific (wood combustion and vehicles) PM samples was also undertaken, and the results of these analyses are included in this thesis.</p>

Simulation of Wood Combustion in PATO Using a Detailed Pyrolysis Model Coupled to fireFoam

The numerical simulation of fire propagation requires capturing the coupling between wood pyrolysis, which leads to the production of various gaseous species, and the combustion of these species in the flame, which produces the energy that sustains the pyrolysis process. Experimental and numerical works of the fire community are targeted towards improving the description of the pyrolysis process to better predict the rate of production and the chemical nature of the pyrolysis gases. We know that wood pyrolysis leads to the production of a large variety of chemical species: water, methane, propane, carbon monoxide and dioxide, phenol, cresol, hydrogen, etc. With the idea of being able to capitalize on such developments to study more accurately the physics of fire propagation, we have developed a numerical framework that couples a detailed three-dimensional pyrolysis model and fireFoam. In this article, we illustrate the capability of the simulation tool by treating the combustion of a wood log. Wood is considered to be composed of three phases (cellulose, hemicellulose and lignin), each undergoing parallel degradation processes leading to the production of methane and hydrogen. We chose to simplify the gas mixture for this first proof of concept of the coupling of a multi-species pyrolysis process and a flame. In the flame, we consider two separate finite-rate combustion reactions for methane and hydrogen. The flame evolves during the simulation according to the concentration of the two gaseous species produced from the material. It appears that introducing different pyrolysis species impacts the temperature and behavior of the flame.

Physical and chemical properties of black carbon and organic matter from different combustion and photochemical sources using aerodynamic aerosol classification

The physical and chemical properties of black carbon (BC) and organic aerosols are important for predicting their radiative forcing in the atmosphere. During the Soot Aerodynamic Size Selection for Optical properties (SASSO) project and a EUROCHAMP-2020 transnational access project, different types of light-absorbing carbon were studied, including BC from catalytically stripped diesel exhaust, an inverted flame burner, a colloidal graphite standard (Aquadag) and controlled flaming wood combustion. Brown carbon (BrC) was also investigated in the form of organic aerosol emissions from wood burning (pyrolysis and smouldering) and from the nitration of secondary organic aerosol (SOA) proxies produced in a photochemical reaction chamber. Here we present insights into the physical and chemical properties of the aerosols, with optical properties presented in subsequent publications. The dynamic shape factor (χ) of BC particles and material density (ρm) of organic aerosols was investigated by coupling a charging-free Aerodynamic Aerosol Classifier (AAC) with a Centrifugal Particle Mass Analyzer (CPMA) and a Scanning Mobility Particle Sizer (SMPS). The morphology of BC particles was captured by transmission electron microscopy (TEM). For BC particles from the diesel engine and flame burner emissions, the primary spherule sizes were similar, around 20 nm. With increasing particle size, BC particles adopted more collapsed/compacted morphologies for the former source but tended to show more aggregated morphologies for the latter source. For particles emitted from the combustion of dry wood samples, the χ of BC particles and the ρm of organic aerosols were observed in the ranges 1.8–2.17 and 1.22–1.32 g cm−3, respectively. Similarly, for wet wood samples, the χ and ρm ranges were 1.2–1.85 and 1.44–1.60 g cm−3, respectively. Aerosol mass spectrometry measurements show no clear difference in mass spectra of the organic aerosols in individual burn phases (pyrolysis or smouldering phase) with the moisture content of the wood samples. This suggests that the effect moisture has on the organic chemical profile of wood burning emissions is through changing the durations of the different phases of the burn cycle, not through the chemical modification of the individual phases. In this study, the incandescence signal of a Single Particle Soot Photometer (SP2) was calibrated with three different types of BC particles and compared with that from an Aquadag standard that is commonly used to calibrate SP2 incandescence to a BC mass. A correction factor is defined as the ratio of the incandescence signal from an alternative BC source to that from the Aquadag standard and took values of 0.821 ± 0.002 (or 0.794 ± 0.005), 0.879 ± 0.003 and 0.843 ± 0.028 to 0.913 ± 0.009 for the BC particles emitted from the diesel engine running under hot (or cold idle) conditions, the flame burner and wood combustion, respectively. These correction factors account for differences in instrument response to BC from different sources compared to the standardised Aquadag calibration and are more appropriate than the common value of 0.75 recommended by Laborde et al. (2012b) when deriving the mass concentration of BC emitted from diesel engines. Quantifying the correction factor for many types of BC particles found commonly in the atmosphere may enable better constraints to be placed on this factor depending on the BC source being sampled and thus improve the accuracy of future SP2 measurements of BC mass concentrations.

Technical note: Pyrolysis principles explain time-resolved organic aerosol release from biomass burning

Emission of organic aerosol (OA) from wood combustion is not well constrained; understanding the governing factors of OA emissions would aid in explaining the reported variability. Pyrolysis of the wood during combustion is the process that produces and releases OA precursors. We performed controlled pyrolysis experiments at representative combustion conditions. The conditions changed were the temperature, wood length, wood moisture content, and wood type. The mass loss of the wood, the particle concentrations, and light-gas concentrations were measured continuously. The experiments were repeatable as shown by a single experiment, performed nine times, in which the real-time particle concentration varied by a maximum of 20 %. Higher temperatures increased the mass loss rate and the released concentration of gases and particles. Large wood size had a lower yield of particles than the small size because of higher mass transfer resistance. Reactions outside the wood became important between 500 and 600 ∘C. Elevated moisture content reduced product formation because heat received was shared between pyrolysis reactions and moisture evaporation. The thermophysical properties, especially the thermal diffusivity, of wood controlled the difference in the mass loss rate and emission among seven wood types. This work demonstrates that OA emission from wood pyrolysis is a deterministic process that depends on transport phenomena.