Aerosol Mass Spectral Profiles from NAMaSTE Field-Sampled South Asian Combustion Sources

Abstract

Unit mass resolution mass spectral profiles of nonrefractory submicron aerosol were retrieved from undersampled atmospheric emission sources common to South Asia using a “mini” aerosol mass spectrometer. Emission sources including wood- and dung-fueled cookstoves, agricultural residue burning, garbage burning, engine exhaust, and coal-fired brick kilns were sampled during the 2015 Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) campaign. High-resolution peak fitting estimates of the mass spectra were used to characterize ions found within each source profile and help identify mass spectral signatures unique to aerosol emissions from the investigated source types. The first aerosol mass spectral profiles of dung burning, charcoal burning, garbage burning, and brick kilns are provided in this work. The online aerosol mass spectra show that organics were generally the dominant component of the nonrefractory aerosol. However, inorganic aerosol components including ammonium and chloride were significant in dung- and charcoal-fired cookstove emissions and sulfate compounds were major components of the coal-fired brick kiln emissions. Organic mass spectra from both the charcoal burning and zigzag brick kiln were dominated by nitrogen-containing ions thought to be from the electron ionization of amines and amides contained in the emissions. The mixed garbage burning emissions profiles were dominated by plastic combustion with very low fractions of organic markers associated with biomass burning. The plastic burning emissions were associated with enhanced organic signal at mass-to-charge (m/z) 104 and m/z 166, which could be useful fragment ion indicators for garbage burning in ambient aerosol profiles. Finally, a framework for the identification of emission sources using the unit mass resolution organic mass fractions at m/z 55 (f 55), m/z 57 (f 57), and m/z 60 (f 60) is proposed in this work. Plotting the ratio of f 55 to f 57 versus f 60 is found to be effective for the identification of emissions by the fuel type and even useful in separating emissions of similar source types. Although the sample size was limited, these results give further context to the aerosol and gas-phase emission factors presented in other NAMaSTE works and provide a critical reference for future aerosol composition measurements in South Asia.

Submicron Aerosol Composition and Source Contribution across the Kathmandu Valley, Nepal, in Winter

“…We converted the high-resolution AMS OA PMF factor mass spectra from NAMaSTE1 to unit mass resolution (UMR) to better match NAMaSTE2 resolution to further corroborate and identify factors. The mass spectra measured for primary emission sources in NAMaSTE1 can be seen to closely resemble the NAMaSTE2 AMS-PMF ambient factors . A more detailed comparison of the factors comparing relative intensities for all peaks is in Figure S6.…”

“…SO 4 is the form of sulfur most prevalent in the aerosol phase . Primary emissions from coal combustion and brick kilns are the suspected dominant source of aerosol sulfate in the Kathmandu Valley; the burning of agricultural residue contributed to a small degree. , SO 4 as measured by the AMS has low correlation with BBOA (slope = 0.54, R 2 = 0.17, Figure S8), but correlates well with sLOA (slope = 0.47, R 2 = 0.57). Brick kilns have a large sulfate emission factor .…”

“…The mass spectra measured for primary emission sources in NAMaSTE1 can be seen to closely resemble the NAMaSTE2 AMS-PMF ambient factors. 29 A more detailed comparison of the factors comparing relative intensities for all peaks is in Figure S6 . The NAMaSTE2 HOA mass spectrum corresponds well to both fresh emissions from idling motorcycles ( R 2 = 0.95) and the ambient high-resolution (HR) AMS-PMF HOA factor ( R 2 = 0.90) measured in NAMaSTE1.…”

“…The previous air quality campaigns including the initial Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) established the primary regional sources of particulate matter (PM) as vehicle emissions, coal combustion, biomass burning (BB) for cooking and agriculture, trash burning (TB), dust, and industry. − Most PM 2.5 in Kathmandu Valley is locally generated, though wind introduces some fraction of pollutants from the IGP. , Elevated black carbon (BC) levels are typical in the region. − Previous studies such as sustainable atmosphere for the Kathmandu Valley (SusKat) have measured gas-phase and PM 10 compositions, noted the effects of primary and secondary sources on air quality in the region, ,− and apportioned pre-monsoon PM measurements to their sources. ,,, However, wintertime submicron aerosol composition and the spatial impact of individual point sources on ambient concentrations remained vague.…”

“… 21 , 22 Elevated black carbon (BC) levels are typical in the region. 23 − 25 Previous studies such as sustainable atmosphere for the Kathmandu Valley (SusKat) have measured gas-phase and PM 10 compositions, noted the effects of primary and secondary sources on air quality in the region, 16 , 26 − 29 and apportioned pre-monsoon PM measurements to their sources. 18 , 20 , 30 , 31 However, wintertime submicron aerosol composition and the spatial impact of individual point sources on ambient concentrations remained vague.…”