Aerosol Optical Properties and Climate Implications of Emissions from Traditional and Improved Cookstoves

Evaluating the Laboratory Performance of Pellet-Fueled Semigasifier Cookstoves

This study examines three representative semigasifier cookstove models each burning four types of pelletized-biomass fuel (hardwood, peanut hull, rice husk, and wheat straw) using the International Organization for Standardization (ISO) 19867-1:2018 protocol. ISO tier ratings for fine particulate matter (PM2.5) and carbon monoxide (CO) emissions ranged 1-4 and 2-5 (where 5 = cleanest), respectively, suggesting that pellet-fueled cookstoves may provide substantial emissions reductions, dependent upon stove/fuel matching and operation, over other biomass-fueled cooking alternatives. PM2.5 emission factors based on useful energy delivered (EFd) varied by up to 25-fold, and organic and elemental carbon (OC and EC) EFd values respectively varied by >200- and ∼100-fold, reflecting complex variability in PM2.5 composition. These semigasifier cookstoves showed higher ultrafine particle (UFP) emissions but lower bulk PM2.5 emissions. Operation of pellet-fueled cookstoves at higher firepower resulted in higher PM2.5 and UFP emission factors and higher EC-to-total-carbon ratios; operation at lower firepower resulted in higher gaseous pollutant emission factors. Results of this work provide technical guidance for stove developers, users, and policy-makers. These ISO-protocol-based emission factors are also pertinent to health and climate modeling efforts.

A systematic review of the variability of freshly-emitted and aged black carbon based on various measurement techniques

Black carbon (BC) poses acute negative health and environmental impacts. Accurate BC quantification is important for assessing its impacts and developing effective control strategies. However, the unclear optical properties and numerous methods of BC restrict its accurate quantification. Elemental carbon (EC), refractory black carbon (rBC), and equivalent black carbon (eBC) are terminology used for BC quantification by various techniques, with an essential parameter of mass absorption cross-section (MAC) characterizing its optical properties. This review summarizes the measurement principles, along with the advantages, limitations, and uncertainties of mainstream instruments used for BC quantification, based on findings from numerous studies. Then, we categorically compared the MAC of BC for different emission sources and regions, and those are not consistent. The MAC values of freshly-emitted and aged BC are both influenced by the combustion sources, while the transport process present significant impact on aged BC. Average MAC values of BC for urban, rural, and other areas are 10.1 ± 3.7 m2/g, 13.4 ± 5.7 m2/g, and 13.7 ± 8.2 m2/g at 550 nm, respectively. Furthermore, we systematically explored the relationship between eBC, EC, and rBC of freshly-emitted and aged BC to establish unambiguous links between these terms. Averaged mass ratios of eBC/EC, eBC/rBC and EC/rBC are 0.81, 0.94, and 1.32 for freshly-emitted BC, 1.17, 2.14, and 1.60 for aged BC, respectively. Overall, it is urgent to establish standard methods for accurate BC quantification in the future to reduce the uncertainty of quantitative results by different techniques.

Refined mass absorption cross-section of black carbon from typical non-road mobile machinery in China based on real-world measurements

Non-road mobile machinery (NRMM) is becoming a more prominent contribution of black carbon (BC), and mass absorption cross-section (MAC) as an essential parameter to characterize the BC optical property is still not clear. In this study, we explored the impacts of key factors on the MAC of BC based on real-world measurements from 41 typical NRMM. We characterized the organic carbon (OC) and elemental carbon (EC), and found MAC values of BC from NRMM increase as the OC/EC mass ratios increase, since the OC coating can enhance BC light absorption. With more stringent emission standards, the MAC values of all tested NRMM show a significant decreasing trend. Meanwhile, we found the absorption coefficients obtained by filter-based (bfilter) and in-situ-based (bin-situ) methods present good correlation for NRMM in this study, but bfilter are significantly higher than bin-situ when bfilter are above 40,000 Mm-1. Furthermore, we have refined the MAC values under different emission standards, and recommended a more appropriate MAC value (11.5 ± 3.4 m2/g) of NRMM at 550 nm wavelength, which is 1.5 times of the MAC value (7.5 m2/g) commonly used in previous studies. Our results will be indispensable for accurate BC quantification from NRMM and climate radiative effects prediction.

Particulate matters, aldehydes, and polycyclic aromatic hydrocarbons produced from deep-frying emissions: comparisons of three cooking oils with distinct fatty acid profiles

It is recognized that hazardous emissions produced from frying oils may be related to oil properties, particularly the fatty acid composition. However, investigations have been limited and partial. In this work, the emissions from deep-frying foods with three oils (palm, olive, and soybean oils) with distinct fatty acid profiles were comprehensively examined in a simulated kitchen, and the interrelationship among emitted substances, oil quality parameters, and fatty acids profiles was explored. Firstly, palm oil emitted the highest number concentration of total particle matters ((3895 ± 1796) × 103 #/cm3), mainly in the Aitken mode (20-100 nm). We observed a positive correlation between particle number concentration and levels of palmitic acid, a major saturated fatty acid (SAFA) (rs = 0.73, p < 0.05), and total polar compounds (TPC) (rs = 0.68, p < 0.05) in the fried oil, a degradation marker which was also positively correlated with that of black carbon (BC) (rs = 0.68, p < 0.05). Secondly, soybean oil emitted the highest level of gaseous aldehydes (3636 ± 607 μg/m3), including acrolein, propinoaldehyde, crotonaldehyde, hexanal, and trans-2-heptenal; the total aldehyde concentration were positively correlated with α-linolenic acid (ALA) percentage (rs = 0.78, p < 0.01), while hexanal and trans-2-heptenal were with linoleic acid (LA) (rs = 0.73 and 0.67, p < 0.05). LA and ALA were two major polyunsaturated fatty acids in non-tropical plant oils. Thirdly, palm oil emitted the most particle-bound polycyclic aromatic hydrocarbons (PAHs), and a positive association was discovered between two PAHs and SAFA percentage. Olive oil seems superior to soybean and palm oils with regards to toxic emissions during deep-frying.

Mass absorption cross-section of black carbon from residential biofuel stoves and diesel trucks based on real-world measurements

Black carbon (BC) as an important part of atmospheric aerosols imposes adverse effects on atmospheric visibility, health, and climate change. Mass absorption cross-section (MAC_BC) is an essential parameter in BC quantitative and model research, which is of growing concern in recent decades. In this study, we conducted real-world measurements on BC emissions from two major sources of residential biofuel stoves and diesel trucks. BC emissions and MAC_BC values are quantified based on the photoacoustic and thermo-optical methods. The impacts of typical factors from biofuel stoves (biofuel and stove types) and diesel trucks (vehicle types, emission standards, and driving conditions) on BC/EC, MAC_BC values, and the relationships between BC and EC, BC/PM_2.5 and MAC_BC are analyzed comprehensively. We find the BC and EC emissions from these two sources present good correlations, and those emissions are almost equal from diesel trucks, while the EC emissions from biofuel burning are slightly higher than BC. The typical factors for analysis may affect the optical properties of BC, and then will affect the mass ratio of BC/EC, indirectly. We have calculated the equivalent MAC_BC values and compared those with previous studies. Then, we further divided the equivalent MAC_BC values under several typical factors, which are 5.84 and 2.71 m²/g for improved and simple biofuel stoves, and 5.91 and 4.64 m²/g for light-duty and heavy-duty diesel trucks, respectively. Furthermore, the MAC_BC and BC/PM_2.5 under the main operational metrics generally present good correlations. Our results will help to enhance the understanding of MAC_BC and provide effective data support for BC quantification and atmospheric model research.

Real-time measurements of black carbon and other pollutant emissions from residential biofuel stoves in rural China

Biofuel stoves are an important source of black carbon (BC) emissions, which have adverse effects on the environment and human health, especially in rural areas. However, there have been only limited studies of BC emissions from residential biofuel stoves based on real-time measurements. In this study, a photo-acoustic extinctiometer (PAX)-based real-time measurement system was employed to monitor the emission characteristics of corncobs, corn stalks, cotton stalks and poplar branches in simple or improved stoves (with a total of 16 units) in Hebei Province, China. The real-time and phased emissions of BC, fine particulate matter (PM_2.5), carbon monoxide (CO) and carbon dioxide (CO₂) were assessed, and the effects of stove type and fuel on emissions were analyzed. Under the same conditions, polar branches were associated with the highest BC emission factors (EFs) of up to 2.64 ± 0.42 g kg^-1, while the EFs for improved stoves were higher than those for simple stoves. During the ignition phase, BC emissions were found to be low, while the later addition of fuel dramatically increased emissions, followed by a gradual decrease until the next fuel addition. The phased results show that the flaming phase had the highest BC emission rate, the fuel addition phase was associated with the highest BC EF. The BC emission rates and EFs for the ignition, fuel addition, flaming and smoldering phases ranged from 0.0014-0.014, 0.11-6.32, 0.18-2.24 and 0.03-0.32 mg s^-1, and from 0.04-0.18, 0.38-9.53, 0.45-3.55 and 0.12-1.01 g kg^-1, respectively. This study assessed the BC emissions from residential biofuel stoves using a larger sample size than in prior work. The results increase our understanding of the BC emissions process, which is helpful in terms of improving the accuracy of BC EF estimations. The real-time measurement process described herein is also expected to provide new approaches to minimizing BC emissions.

Characterizing dynamic relationships between burning rate and pollutant emission rates in a forced-draft gasifier stove consuming biomass pellet fuels

Biomass is a dominant solid fuel type worldwide. Traditional biomass combustion leads to severe indoor and ambient environmental problems. Biomass pellet utilization in forced-draft gasifier stoves is regarded as an improved approach to these problems. Previous studies on forced-draft biomass stoves mainly considered average emission amounts and lacked details of the combustion properties and dynamic correlations between emissions and combustion. This study used a dynamic measurement system to test a typical forced-draft gasifier stove consuming wood pellets and maize straw pellets. Real-time fuel burning rate, that partly reflects the combustion performance, and CO, NO_x and PM_2.5 emission rates, over a whole combustion course, were monitored. In all tests, the burning rate rose to a high and stable level, and then sharply subsided. CO, NO_x and PM_2.5 emission rates varied across the combustion course. CO (NO_x) emissions have a negative (positive) logarithmic linear relationship with burning rate, while no consistent relationship was observed for PM_2.5 emission rate. The identified relationships between burning rate and pollutant emission rates suggest the possibility of estimating emission performance of forced-draft biomass pellet stoves based on combustion indicators, or vice versa.