Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE): emissions of trace gases and light-absorbing carbon from wood and dung cooking fires, garbage and crop residue burning, brick kilns, and other sources

Abstract

Abstract. The Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) campaign took place in and around the Kathmandu Valley and in the Indo-Gangetic Plain (IGP) of southern Nepal during April 2015. The source characterization phase targeted numerous important but undersampled (and often inefficient) combustion sources that are widespread in the developing world such as cooking with a variety of stoves and solid fuels, brick kilns, open burning of municipal solid waste (a.k.a. trash or garbage burning), crop residue burning, generators, irrigation pumps, and motorcycles. NAMaSTE produced the first, or rare, measurements of aerosol optical properties, aerosol mass, and detailed trace gas chemistry for the emissions from many of the sources. This paper reports the trace gas and aerosol measurements obtained by Fourier transform infrared (FTIR) spectroscopy, whole-air sampling (WAS), and photoacoustic extinctiometers (PAX; 405 and 870 nm) based on field work with a moveable lab sampling authentic sources. The primary aerosol optical properties reported include emission factors (EFs) for scattering and absorption coefficients (EF Bscat, EF Babs, in m2 kg−1 fuel burned), single scattering albedos (SSAs), and absorption Ångström exponents (AAEs). From these data we estimate black and brown carbon (BC, BrC) emission factors (g kg−1 fuel burned). The trace gas measurements provide EFs (g kg−1) for CO2, CO, CH4, selected non-methane hydrocarbons up to C10, a large suite of oxygenated organic compounds, NH3, HCN, NOx, SO2, HCl, HF, etc. (up to ∼ 80 gases in all). The emissions varied significantly by source, and light absorption by both BrC and BC was important for many sources. The AAE for dung-fuel cooking fires (4.63 ± 0.68) was significantly higher than for wood-fuel cooking fires (3.01 ± 0.10). Dung-fuel cooking fires also emitted high levels of NH3 (3.00 ± 1.33 g kg−1), organic acids (7.66 ± 6.90 g kg−1), and HCN (2.01 ± 1.25 g kg−1), where the latter could contribute to satellite observations of high levels of HCN in the lower stratosphere above the Asian monsoon. HCN was also emitted in significant quantities by several non-biomass burning sources. BTEX compounds (benzene, toluene, ethylbenzene, xylenes) were major emissions from both dung- (∼ 4.5 g kg−1) and wood-fuel (∼ 1.5 g kg−1) cooking fires, and a simple method to estimate indoor exposure to the many measured important air toxics is described. Biogas emerged as the cleanest cooking technology of approximately a dozen stove–fuel combinations measured. Crop residue burning produced relatively high emissions of oxygenated organic compounds (∼ 12 g kg−1) and SO2 (2.54 ± 1.09 g kg−1). Two brick kilns co-firing different amounts of biomass with coal as the primary fuel produced contrasting results. A zigzag kiln burning mostly coal at high efficiency produced larger amounts of BC, HF, HCl, and NOx, with the halogenated emissions likely coming from the clay. The clamp kiln (with relatively more biomass fuel) produced much greater quantities of most individual organic gases, about twice as much BrC, and significantly more known and likely organic aerosol precursors. Both kilns were significant SO2 sources with their emission factors averaging 12.8 ± 0.2 g kg−1. Mixed-garbage burning produced significantly more BC (3.3 ± 3.88 g kg−1) and BTEX (∼ 4.5 g kg−1) emissions than in previous measurements. For all fossil fuel sources, diesel burned more efficiently than gasoline but produced larger NOx and aerosol emission factors. Among the least efficient sources sampled were gasoline-fueled motorcycles during start-up and idling for which the CO EF was on the order of ∼ 700 g kg−1 – or about 10 times that of a typical biomass fire. Minor motorcycle servicing led to minimal if any reduction in gaseous pollutants but reduced particulate emissions, as detailed in a companion paper (Jayarathne et al., 2016). A small gasoline-powered generator and an “insect repellent fire” were also among the sources with the highest emission factors for pollutants. These measurements begin to address the critical data gap for these important, undersampled sources, but due to their diversity and abundance, more work is needed.

Open burning of rice, corn and wheat straws: primary emissions, photochemical aging, and secondary organic aerosol formation

“…Akagi et al (2011) updated the emission data for 14 types of biomass burning, and newly identified species were included. Since biomass types and combustion conditions may differ in different studies, reported emission factors are highly variable, especially for agricultural residue burning (Li et al, 2007(Li et al, , 2017Cao et al, 2008;Zhang et al, 2008;Yokelson et al, 2011;Brassard et al, 2014;Sanchis et al, 2014;Ni et al, 2015;Kim Oanh et al, 2015;Stockwell et al, 2016;Bruns et al, 2017;Tkacik et al, 2017). Moreover, previous studies on agricultural residue burning were mostly carried out near fire spots or in chambers with low dilution ratios.…”

Chemical characteristics of submicron particles at the central Tibetan Plateau: insights from aerosol mass spectrometry

“…Burning of biomass fuels and wildfires in the southern Himalaya and South Asia are thought to be important sources for black carbon (Stone et al, 2010;Engling et al, 2011;Kumar et al, 2011). However, a recent study shows that sources of black carbon in the region of South Asia are highly complex, including emissions from low-efficiency transport tools and cooking using cow dung and biogas (Stockwell et al, 2016). These burning activities also emit other species such as organic and inorganic particulate species and volatile organic compounds, which generate a well-mixed aerosol plume eventually via processes such as coagulation, evaporation, oxidation, and condensation.…”

Black Carbon, Organic Carbon, and Co-Pollutants Emissions and Energy Efficiency from Artisanal Brick Production in Mexico

“…Fifteen kilns in India and two in Vietnam representing five types of kiln designs were 20 sampled for their CO, CO 2 , SO 2 , and their PM 2.5 and elemental carbon (EC) emission factors and optical properties . Stockwell et al (2016) measured a "zig-zag" kiln and a batch-type clamp kiln burning coal as fuel in Nepal to obtain emission factors for a large suite of gases and PM composition. Overall, the results from these studies indicate that emission factors are highly variable and depend on fuel type, feeding patterns, fraction of internal and external fuel, and kiln designs.…”