Cheryl L. Weyant

A large concern with estimates of climate and health co-benefits of “clean” cookstoves from controlled emissions testing is whether results represent what actually happens in real homes during normal use. A growing body of evidence indicates that in-field emissions during daily cooking activities differ substantially from values obtained in laboratories, with correspondingly different estimates of co-benefits. We report PM_2.5 emission factors from uncontrolled cooking (n = 7) and minimally controlled cooking tests (n = 51) using traditional chulha and angithi stoves in village kitchens in Haryana, India. Minimally controlled cooking tests (n = 13) in a village kitchen with mixed dung and brushwood fuels were representative of uncontrolled field tests for fine particulate matter (PM_2.5), organic and elemental carbon (p > 0.5), but were substantially higher than previously published water boiling tests using dung or wood. When the fraction of nonrenewable biomass harvesting, elemental, and organic particulate emissions and modeled estimates of secondary organic aerosol (SOA) are included in 100 year global warming commitments (GWC₁₀₀), the chulha had a net cooling impact using mixed fuels typical of the region. Correlation between PM_2.5 emission factors and GWC (R² = 0.99) implies these stoves are climate neutral for primary PM_2.5 emissions of 8.8 ± 0.7 and 9.8 ± 0.9 g PM_2.5/kg dry fuel for GWC₂₀ and GWC₁₀₀, respectively, which is close to the mean for biomass stoves in global emission inventories.

Traditional biomass stoves are a major global contributor to emissions that impact climate change and health. This paper reports emission factors of particulate matter (PM_2.5), carbon monoxide (CO), organic carbon (OC), black carbon (EC), optical absorption, and scattering from 46 South Asian, 48 Tibetan and 4 Ugandan stoves. These measurements plus a literature review provide insight into the robustness of emission factors used in emission inventories. Tibetan dung stoves produced high average PM_2.5 emission factors (23 and 43 gkg^-1 for chimney and open stoves) with low average EC (0.3 and 0.7 gkg^-1, respectively). Comparatively, PM_2.5 from South Asian stoves (7 gkg^-1) was in the range of previous measurements and near values used in inventories. EC emission factors varied between stoves and fuels (p < 0.001), without corresponding differences in absorption; stoves that produced little EC, produced enough brown carbon to have about the same absorption as stoves with high EC emissions. In Tibetan dung stoves, for example, OC contributed over 20% of the absorption. Overall, EC emission factors were not correlated with PM_2.5 and were constrained to low values, relative to PM_2.5, over a wide range of combustion conditions. The average measured EC emission factor (1 gkg^-1) was near current inventory estimates.

Understanding how fuels and stoves are used to meet a diversity of household needs is an important step in addressing the factors leading to continued reliance on polluting devices, and thereby improving household energy programs. In Nepal and many other countries dependent on solid fuel, efforts to mitigate the impacts of residential solid fuel use have emphasized cooking while focusing less on other solid fuel dependent end-uses. We employed a four-season fuel assessment in a cohort of 110 households residing in two elevation regions of the Far-Western Development Region (Province 7) of Nepal. Household interviews and direct fuel weights were used to assess seasonality in fuel consumption and its association with stoves that met cooking and non-cooking needs. Per-capita fuel consumption in winter was twice that of other measured seasons, on average. This winter increase was attributed to greater prevalence of use and fuel consumption by supplemental stoves, not the main cooking stove. End-use profiles showed that fuel was used in supplemental stoves to meet the majority of non-meal needs in the home, notably water heating and preparation of animal food. This emphasis on fuels, stoves, and the satisfaction of energy needs-rather than just stoves or fuels-leads to a better understanding of the factors leading to device and fuel choice within households.

Approximately 150 billion cubic meters (BCM) of natural gas is flared and vented in the world annually, emitting greenhouse gases and other pollutants with no energy benefit. About 7 BCM per year is flared in the United States, and half is from North Dakota alone. There are few emission measurements from associated gas flares and limited black carbon (BC) emission factors have been previously reported from the field. Emission plumes from 26 individual flares in the Bakken formation in North Dakota were sampled. Methane, carbon dioxide, and BC were measured simultaneously, allowing the calculation of BC mass emission factors using the carbon balance method. Particle optical absorption was measured using a three-wavelength particle soot absorption photometer (PSAP) and BC particle number and mass concentrations were measured with a single particle soot photometer. The BC emission factors varied over 2 orders of magnitude, with an average and uncertainty range of 0.14 ± 0.12 g/kg hydrocarbons in associated gas and a median of 0.07 g/kg which represents a lower bound on these measurements. An estimation of the BC emission factor derived from PSAP absorption provides an upper bound at 3.1 g/kg. These results are lower than previous estimations and laboratory measurements. The BC mass absorption cross section was 16 ± 12 m²/g BC at 530 nm. The average absorption Ångström exponent was 1.2 ± 0.8, suggesting that most of the light absorbing aerosol measured was black carbon and the contribution of light absorbing organic carbon was small.