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

摘要

The Nepal Ambient Monitoring andSource Testing Experiment (NAMaSTE) campaign took place in and around theKathmandu Valley and in the Indo-Gangetic Plain (IGP) of southernNepal during April 2015. The source characterization phase targeted numerousimportant but undersampled (and often inefficient) combustion sources thatare widespread in the developing world such as cooking with a variety ofstoves 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, aerosolmass, and detailed trace gas chemistry for the emissions from many of thesources. This paper reports the trace gas and aerosol measurements obtainedby Fourier transform infrared (FTIR) spectroscopy, whole-air sampling (WAS),and photoacoustic extinctiometers (PAX; 405 and 870 nm) based on field workwith a moveable lab sampling authentic sources. The primary aerosol opticalproperties reported include emission factors (EFs) for scattering andabsorption coefficients (EF , EF ,in m kg fuel burned), single scattering albedos (SSAs), and absorptionÅngström exponents (AAEs). From these data we estimate black andbrown carbon (BC, BrC) emission factors (g kg fuel burned). The tracegas measurements provide EFs (g kg) for CO, CO, CH,selected non-methane hydrocarbons up to C, a large suite of oxygenatedorganic compounds, NH, HCN, NO, SO, HCl, HF, etc. (up to ∼ 80 gases in all).The emissions varied significantly by source, and light absorption by bothBrC and BC was important for many sources. The AAE for dung-fuelcooking fires (4.63 ± 0.68) was significantly higher than forwood-fuel cooking fires (3.01 ± 0.10). Dung-fuel cooking fires alsoemitted high levels of NH (3.00 ± 1.33 g kg), organic acids(7.66 ± 6.90 g kg), and HCN (2.01 ± 1.25 g kg), where the lattercould contribute to satellite observations of high levels of HCN in thelower stratosphere above the Asian monsoon. HCN was also emitted insignificant quantities by several non-biomass burning sources. BTEXcompounds (benzene, toluene, ethylbenzene, xylenes) were major emissionsfrom both dung- (∼ 4.5 g kg) and wood-fuel (∼ 1.5 g kg) cooking fires, and a simple method to estimate indoor exposure tothe many measured important air toxics is described. Biogas emerged as thecleanest cooking technology of approximately a dozen stove–fuel combinationsmeasured. Crop residue burning produced relatively high emissions ofoxygenated organic compounds (∼ 12 g kg) and SO (2.54 ± 1.09 g kg). Two brick kilns co-firing different amounts of biomasswith coal as the primary fuel produced contrasting results. A zigzag kilnburning mostly coal at high efficiency produced larger amounts of BC, HF,HCl, and NO, with the halogenated emissions likely coming from theclay. The clamp kiln (with relatively more biomass fuel) produced muchgreater quantities of most individual organic gases, about twice as muchBrC, and significantly more known and likely organic aerosol precursors.Both kilns were significant SO sources with their emission factorsaveraging 12.8 ± 0.2 g kg. Mixed-garbage burning producedsignificantly more BC (3.3 ± 3.88 g kg) and BTEX (∼ 4.5 g kg) emissions than in previous measurements. For all fossil fuel sources,diesel burned more efficiently than gasoline but produced larger NOand aerosol emission factors. Among the least efficient sources sampled weregasoline-fueled motorcycles during start-up and idling for which the CO EFwas on the order of ∼ 700 g kg – or about 10 times that of atypical biomass fire. Minor motorcycle servicing led to minimal if anyreduction in gaseous pollutants but reduced particulate emissions, asdetailed in a companion paper (Jayarathne et al., 2016). A smallgasoline-powered generator and an “insect repellent fire” were also amongthe sources with the highest emission factors for pollutants. Thesemeasurements begin to address the critical data gap for these important,undersampled sources, but due to their diversity and abundance, more work isneeded.