Emissions of biogenic volatile organic compounds and subsequent formation of secondary organic aerosols in a <I>Larix kaempferi</I> forest

Abstract

Abstract. We conducted simultaneous measurements of concentrations and above-canopy fluxes of isoprene and α-pinene, along with their oxidation products in aerosols in a Larix kaempferi (Japanese larch) forest in summer 2012. Vertical profiles of isoprene showed the maximum concentration near the forest floor with a peak around noon, whereas oxidation products of isoprene, i.e., methacrolein (MACR) and methyl vinyl ketone (MVK), showed higher concentrations near the canopy level of the forest. The vertical profile suggests large emissions of isoprene near the forest floor, likely due to Dryopteris crassirhizoma (a fern species), and the subsequent reaction within the canopy. The concentrations of α-pinene also showed highest values near the forest floor, with maximums in the early morning and late afternoon. The vertical profiles of α-pinene suggest its large emissions from soil and litter in addition to emissions from L. kaempferi leaves at the forest site. Isoprene and its oxidation products in aerosols exhibited similar diurnal variations within the forest canopy, providing evidence of secondary organic aerosol (SOA) formation via oxidation of isoprene most likely emitted from the forest floor. Although high abundance of α-pinene was observed in the morning, its oxidation products in aerosols showed peaks in daytime, due to a time lag between the emission and atmospheric reactions of α-pinene to form SOA. Positive matrix factorization (PMF) analysis indicated that anthropogenic influence is the most important factor contributing to the elevated concentrations of molecular oxidation products of isoprene-( > 64 %) and α-pinenederived SOA (> 57 %). The combination of the measured fluxes and vertical profiles of biogenic volatile organic compounds (BVOCs) suggests that the inflow of anthropogenic precursors/aerosols likely enhanced the formation of both isoprene SOA and α-pinene SOA within the forest canopy even when the BVOC flux was relatively low. This study highlights the importance of intra-canopy processes that promote biogenic SOA formation in the presence of significant inflow of oxidants together with anthropogenic aerosols and their precursors.

Characterization of organic aerosols from a Chinese megacity during winter: predominance of fossil fuel combustion

“…It is noteworthy that the major source of NO 2 is vehicular exhaust (Kendrick et al, 2015); however, coal combustion can also emit NO x into the atmosphere (Chang et al, 2018). Previous studies have also reported that NO x could affect SOA formation (Kanakidou et al, 2005;Mochizuki et al, 2015). Moreover, PAHs, hopanes and steranes showed another episode on 23 and 24 December 2014, most likely due to a coal combustion event.…”

Process Understanding of Soil BVOC Fluxes in Natural Ecosystems: A Review

“…Plant-emitted biogenic volatile organic compounds (BVOCs) have been extensively studied and the regional and global estimates of plant BVOC emissions are used as key drivers for atmospheric chemistry models to study the impacts of terrestrial BVOCs on the climate system . Soil-related BVOC emissions could also contribute to ecosystem emissions and thereby impact atmospheric chemistry (Kramshøj et al, 2016;Mochizuki et al, 2015;Nölscher et al, 2016), but they have been less well studied than plant emissions. BVOCs can be released through microbial decomposition of plant residues or soil organic carbon (SOC; Aaltonen et al, 2013;Insam & Seewald, 2010;Leff & Fierer, 2008;Stahl & Parkin, 1996), evaporation of litter-stored BVOCs (Aaltonen et al, 2011) and other physical processes (e.g., desorption from leaf litter tissue (Warneke et al, 1999) and from soil organic matter (Bachy et al, 2018;Schade & Custer, 2004)).…”

Fungal spores overwhelm biogenic organic aerosols in a midlatitudinal forest

“…Various observational methods have been applied to explore PBAPs and SOA in natural environment both qualitatively and quantitatively. Applications of ultraviolet aerodynamic particle sizers and wideband integrated bioaerosol sensor based on fluorescence provided much information on the abundances and size distributions of PBAP Pöhlker et al, 2012). In situ observations of SOA are frequently conducted using an aerosol mass spectrometer (AMS) (Zhang et al, 2007).…”

“…Progress is achieved in boreal forest (Kourtchev et al, 2008) and the Amazon (Graham et al, 2003). However, few studies focused on the midlatitudinal forest with high time resolution (Miyazaki et al, 2012;Mochizuki et al, 2015).…”