Laboratory studies of fresh and aged biomass burning aerosols emitted from east African biomass fuels – Part 2: Chemical properties and characterization

Abstract

Abstract. There are many fuels used for domestic purposes in east Africa, producing a significant atmospheric burden of the resulting aerosols, which includes biomass burning particles. However, the aerosol physicochemical properties are poorly understood. Here, combustion of Eucalyptus and Acacia fuels was performed at 500 and 800 °C in a tube furnace, followed by immediate filter collection for fresh samples or introduction into a photochemical chamber to simulate atmospheric photochemical aging under the influence of anthropogenic emissions. The aerosol generated in the latter experiment was collected onto filters after 12 hours of photochemical aging. 500 and 800 °C were selected to simulate smoldering and flaming combustion, respectively, and to cover a range of combustion conditions. Methanol extracts from Teflon filters were analyzed by ultra-performance liquid chromatography interfaced to both a diode array detector and an electrospray ionization high-resolution quadrupole time-of-flight mass spectrometer (UPLC/DAD-ESI-HR-QTOFMS) to determine the light-absorption properties of biomass burning organic aerosol constituents chemically characterized at the molecular level. Few chemical or UV/Visible differences were apparent between samples for either fuel when combusted at 800 °C. Differences in single scattering albedo (SSA) between fresh samples at this temperature were attributed to compounds not captured in this analysis, with eucalyptol being one suspected missing component. For fresh combustion at 500 °C, many species were present, where lignin pyrolysis and distillation products are more prevalent in Eucalyptus, while pyrolysis products of cellulose and at least one nitroaromatic species were more prevalent in Acacia. SSA trends are consistent with this, particularly if the absorption of those chromophores extends to the 500–570 nm region. Upon aging, both show that resorcinol or catechol was removed to the highest degree, and both aerosol types were dominated by loss of pyrolysis and distillation products, though both differed in the specific compounds being consumed by the photochemical aging process.

Impact of combustion conditions on physical and morphological properties of biomass burning aerosol

“…This work was conducted at the North Carolina Agricultural and Technical State University (NCAT) indoor burning facility that has a well-equipped environmental chamber for the measurement of fresh and aged aerosol, which is described in detail elsewhere (Smith et al 2019(Smith et al , 2020a(Smith et al , 2020b. BB aerosol was generated by the combustion of biomass fuel in a tube furnace.…”

Authors Response

“…on chemical composition and characterization published in ACPD (Smith et al, 2020). Further integration of the two manuscripts will be done, and summaries from Part 2 will be incorporated into the revised manuscript.…”

Response to Anonymous Reviewer #2

“…So, we think more studies are needed on biomass combustion. This work is presented as a two-part study, where this part focused on optical properties and chemical composition and characterization is presented in Part II, which is published in ACPD and we will refer the reviewer to the second part for a detailed discussion (Smith et al, 2020). Further integration of the two manuscripts will be done, and summaries from Part 2 will be incorporated into the revised manuscript.…”