Alejandro Keller

Oxidative potential of logwood and pellet burning particles assessed by a novel profluorescent nitroxide probe.

This study reports the potential toxicological impact of particles produced during biomass combustion by an automatic pellet boiler and a traditional logwood stove under various combustion conditions using a novel profluorescent nitroxide probe, BPEAnit. This probe is weakly fluorescent but yields strong fluorescence emission upon radical trapping or redox activity. Samples were collected by bubbling aerosol through an impinger containing BPEAnit solution, followed by fluorescence measurement. The fluorescence of BPEAnit was measured for particles produced during various combustion phases: at the beginning of burning (cold start), stable combustion after refilling with the fuel (warm start), and poor burning conditions. For particles produced by the logwood stove under cold-start conditions, significantly higher amounts of reactive species per unit of particulate mass were observed compared to emissions produced during a warm start. In addition, sampling of logwood burning emissions after passing through a thermodenuder at 250 degrees C resulted in an 80-100% reduction of the fluorescence signal of the BPEAnit probe, indicating that the majority of reactive species were semivolatile. Moreover, the amount of reactive species showed a strong correlation with the amount of particulate organic material. This indicates the importance of semivolatile organics in particle-related toxicity. Particle emissions from the pellet boiler, although of similar mass concentration, were not observed to lead to an increase in fluorescence signal during any of the combustion phases.

Time-resolved characterization of primary emissions from residential wood combustion appliances

Primary emissions from a log wood burner and a pellet boiler were characterized by online measurements of the organic aerosol (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and of black carbon (BC). The OA and BC concentrations measured during the burning cycle of the log wood burner, batch wise fueled with wood logs, were highly variable and generally dominated by BC. The emissions of the pellet burner had, besides inorganic material, a high fraction of OA and a minor contribution of BC. However, during artificially induced poor burning BC was the dominating species with ∼80% of the measured mass. The elemental O:C ratio of the OA was generally found in the range of 0.2-0.5 during the startup phase or after reloading of the log wood burner. During the burnout or smoldering phase, O:C ratios increased up to 1.6-1.7, which is similar to the ratios found for the pellet boiler during stable burning conditions and higher than the O:C ratios observed for highly aged ambient OA. The organic emissions of both burners have a very similar H:C ratio at a given O:C ratio and therefore fall on the same line in the Van Krevelen diagram.

Organic Emissions from a Wood Stove and a Pellet Stove Before and After Simulated Atmospheric Aging

Logwood and pellet stoves are popular heating sources around the world. The particulate matter emitted from such stoves contains organic particulate matter (OM), soot, and ash, each of which may have significant effects on climate and health. In this study, the primary OM (POM) emitted from a wood stove and a pellet stove operated according to standard Swiss testing protocols were characterized using aerosol mass spectrometry. The POM mass spectra were found to be highly reproducible, and contained CO+ as the dominant ion. Because the POM emitted by such stoves is typically enhanced by the condensation of gaseous organics following atmospheric aging, the secondary OM (SOM) formation potential of these stoves was simulated using the Micro Smog Chamber (MSC) designed by Keller and Burtscher in 2012. In general, OM emission factors from MSC-aged aerosols were comparable to lower-time-resolution results from the literature, although the MSC exposed aerosols to much higher concentrations of oxidants and therefore produced OM that was more oxidized than expected for atmospheric samples. In addition, the logwood-stove particles remained highly aspherical even after oxidation, indicating that mixing with an external aerosol is required for these particles to become spherical. The one exception to this observation occurred when the wood failed to ignite and appeared to generate tar-ball OM particles.

Charge-based personal aerosol samplers

There are several good reasons to use personal monitors for exposure control and health effect studies. But current personal monitoring methods are either not sensitive enough to measure typical ambient concentrations, work offline (masking short exposures to high concentrations), and/or require trained personnel to analyze the data, which makes them difficult to use. For this reason, we propose the use of a diffusion charging sensor as an online personal monitoring method, and present a miniaturized device (45 × 80 ×  200 mm, 770 g) that works on this principle. Our device has a high time resolution and covers typically encountered ambient concentration ranges. It can measure very low particle concentrations of a few hundred particles per cubic centimeter even for ultrafine particles (i.e., two to three orders of magnitude more sensitive than rival technologies), while the upper detection limit is 1 million particles/cm3, which hardly ever occurs in ambient settings. While other methods measure a fixed quantity, the response of our device can be tuned to be proportional to the particle diameter to the power of x, with at least 0.3 ≤ x ≤ 1.35. This opens up the possibility of giving more weight to smaller particles, which is a key feature, since on a per-mass basis, smaller solid particles have been shown to be more toxic than larger ones.

Holzfeuerungen: eine bedeutende Quelle von Feinstaub in der Schweiz

Wood combustion: a substantial source of airborne particulate matter in Switzerland Wood is a renewable energy source. Wood combustion for heating purposes therefore helps in reducing CO2 emissions. However, it often results in high emissions of particulate matter (PM) which includes both black carbon (BC) and organic carbon (OC). PM has adverse health effects and should therefore be minimized. This paper reports on the latest methods to quantify the contribution of wood combustion to PM load and gives values for PM, BC, and OC from wood combustion at a number of different sites in Switzerland. State of the art methods to characterize emissions are presented and examples are given. It is shown that a major fraction of the emissions stems from small wood stoves, where the emissions are especially high during the starting phase. In addition, these small furnaces emit large amounts of gases which are rapidly oxidized and form secondary aerosols in the atmosphere. Improvements in the emissions of small wood s...