Chemical evolution of primary and secondary biomass burning aerosols during daytime and nighttime

Abstract

Abstract. Primary emissions from wood and pellet stoves were aged in an atmospheric simulation chamber under daytime and nighttime conditions. The aerosol was analyzed with online aerosol mass spectrometry and offline Fourier transform infrared spectroscopy (FTIR). Measurements using the two techniques agreed reasonably well in terms of the organic aerosol (OA) mass concentration, OA:OC trends, and concentrations of biomass burning markers – lignin-like compounds and anhydrosugars. Based on aerosol mass spectrometry, around 15 % of the primary organic aerosol (POA) mass underwent some form of transformation during daytime oxidation conditions after 6–10 h of atmospheric exposure. A lesser extent of transformation was observed during the nighttime oxidation. The decay of certain semi-volatile (e.g., levoglucosan) and less volatile (e.g., lignin-like) POA components was substantial during aging, highlighting the role of heterogeneous reactions and gas–particle partitioning. Lignin-like compounds were observed to degrade under both daytime and nighttime conditions, whereas anhydrosugars degraded only under daytime conditions. Among the marker mass fragments of primary biomass burning OA (bbPOA), heavy ones (higher m/z) were relatively more stable during aging. The biomass burning secondary OA (bbSOA) became more oxidized with continued aging and resembled that of aged atmospheric organic aerosols. The bbSOA formed during daytime oxidation was dominated by acids. Organonitrates were an important product of nighttime reactions in both humid and dry conditions. Our results underline the importance of changes to both the primary and secondary biomass burning aerosols during their atmospheric aging. Heavier fragments from aerosol mass spectrometry seldom used in atmospheric chemistry can be used as more stable tracers of bbPOA and, in combination with the established levoglucosan marker, can provide an indication of the extent of bbPOA aging.

Characterization and dark oxidation of the emissions of a pellet stove

“…Sampling on 47 mm PTFE filters (Pall Corporation, 1 cm diameter of the collection surface) was performed at a flow rate of 8 L min −1 for 20 min for primary and aged PM 1 pellet emissions in order to perform offline Fourier transform infrared spectroscopy (FTIR). Details about the FTIR analysis can be found in Yazdani et al 51 …”

Rapid transformation of wildfire emissions to harmful background aerosol

“…, which has been identified as a biomass-burning tracer 10 during aging chamber experiments, also increased during the fire events. However, its concentration was still low and resulted in minor differences in the OA spectrum.…”

“…Our hypothesis is that the biomass burning emissions react rapidly in the atmosphere and are transformed to oxidized OA. The transformations include evaporation of the semi-volatile bbOA components, reactions in the gas phase and then recondensation of the products of the oxidation, heterogeneous reactions of the primary biomass burning with OH and reactions in the aqueous phase (both in clouds and during periods of high RH) 9,10 . This chemical aging of bbOA leads to rapid loss of its organic chemical fingerprints (e.g., levoglucosan), thus resulting in a serious underestimation of its contribution to the OA levels.…”