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

<p><strong>Abstract.</strong> The Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) campaign took place in and around the Kathmandu Valley and in the Indo-Gangetic plains (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 and 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 m<sup>2</sup>/kg fuel burned), single scattering albedo (SSA), and absorption Ångstrӧm exponents (AAE). From these data we estimate black and brown carbon (BC, BrC) emission factors (g/kg fuel burned). The trace gas measurements provide EFs (g/kg) for CO<sub>2</sub>, CO, CH<sub>4</sub>, selected nonmethane hydrocarbons up to C<sub>10</sub>, a large suite of oxygenated organic compounds, NH<sub>3</sub>, HCN, NO<sub><i>x</i></sub>, SO<sub>2</sub>, HCl, HF, etc.; up to ~ 80 gases in all.<br><br> 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 NH<sub>3</sub> (3.00 ± 1.33 g/kg), organic acids (7.66 ± 6.90 g/kg), and HCN (2.01 ± 1.25 g/kg), 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) and wood-fuel (~ 1.5 g/kg) 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) and SO<sub>2</sub> (2.54 ± 1.09 g/kg). Two brick kilns co-firing different amounts of biomass with the primarily coal fuel produced contrasting results. A zig-zag kiln burning mostly coal at high efficiency produced larger amounts of BC, HF, HCl, and NO<sub><i>x</i></sub>, 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 SO<sub>2</sub> sources with their emission factors averaging (12.8 ± 0.2 g/kg). Mixed garbage burning produced significantly 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 NO<subn><i>x</i></sub> 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 – or about ten times that of a typical biomass fire. Minor motorcycle servicing led to minimal if any reduction of 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.</p>

Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE): Emissions of particulate matter from wood and dung cooking fires, garbage and crop residue burning, brick kilns, and other sources

“…The sampled air volume was calculated as the product of the average air flow rate through the filter and total sampling time. The filtered air was then passed to the land-based Fourier transform infrared (LA-FTIR) spectrometer multi-pass cell for the measurement of gas phase species as described by Stockwell et al (2016).…”

“…[CO], methane [CH 4 ], ammonia [NH 3 ], hydrochloric acid [HCl]), non-methane organic gases, and light-absorbing 30 carbon (brown carbon [BrC] and black carbon [BC]) for these sources are reported by Stockwell et al (2016).…”

“…Reported herein are the first detailed chemical profiles for many sources in South Asia, including clamp kilns, garbage burning, and diesel groundwater pumps. These 5 particulate phase measurements, in combination with gas-phase, optical, and additional PM measurements reported in our companion papers by Stockwell et al (2016) and Goetz et al (in preparation-a) provide a detailed chemical description of these source emissions. These new emissions data can be used when expanding and updating emissions inventories, as source profiles in receptor-based source apportionment modeling, or to model exposures to air pollutants.…”

“…In Nepal, they account for 80% of the vehicle fleet, consume 9% of the transport sector's fuel, and are undergoing the fastest growth of any vehicle sector (WECS, 2014;MoPIT, 2014). The motorcycles tested during NAMaSTE were 3-15 years old at the time of sampling and had 4-stroke engines (Stockwell et al, 2016), which is the most common engine type in Nepal 20 (Shrestha et al, 2013). The motorcycles were manufactured in India and because four-stroke engines were not required to have catalytic converters until 2015 in India, it was assumed that the motorcycles tested did not have them (Stockwell et al, 2016).…”

“…The motorcycles tested during NAMaSTE were 3-15 years old at the time of sampling and had 4-stroke engines (Stockwell et al, 2016), which is the most common engine type in Nepal 20 (Shrestha et al, 2013). The motorcycles were manufactured in India and because four-stroke engines were not required to have catalytic converters until 2015 in India, it was assumed that the motorcycles tested did not have them (Stockwell et al, 2016). The absence of a catalytic converter leads to higher PM and PAH emissions, as do cold-starts when the catalyst is not fully operational (Spezzano et al, 2008).…”