Terpene emissions from boreal wetlands can initiate stronger atmospheric new particle formation than boreal forests

Abstract

Aerosols and their interaction with clouds constitute the largest uncertainty in estimating the radiative forcing affecting the climate system. Secondary aerosol formation is responsible for a large fraction of the cloud condensation nuclei in the global atmosphere. Wetlands are important to the budgets of methane and carbon dioxide, but the potential role of wetlands in aerosol formation has not been investigated. Here we use direct atmospheric sampling at the Siikaneva wetland in Finland to investigate the emission of methane and volatile organic compounds, and subsequently formed atmospheric clusters and aerosols. We find that terpenes initiate stronger atmospheric new particle formation than is typically observed over boreal forests and that, in addition to large emissions of methane which cause a warming effect, wetlands also have a cooling effect through emissions of these terpenes. We suggest that new wetlands produced by melting permafrost need to be taken into consideration as sources of secondary aerosol particles when estimating the role of increasing wetland extent in future climate change.

Quiet New Particle Formation in the Atmosphere

“…The previously overlooked phenomenon investigated here, termed "quiet NPF", is taking place outside periods of traditional, regional NPF events. This can be seen either by analyzing long measurement time series where several years of data can be averaged, or by focusing on situations where the boundary layer is extremely stable, like at wetland sites at night (Junninen et al, 2022). Such quiet NPF is not easy to detect but, due to its apparently frequent occurrence, it might produce significant number concentrations of new aerosol particles in comparison with the traditional, regional NPF events.…”

High emission rates and strong temperature response make boreal wetlands a large source of isoprene and terpenes

“…Siikaneva has been a wellestablished site for eddy covariance measurements of greenhouse gases since 2005 (Aurela et al, 2007;Rinne et al, 2007) and has also been part of the integrated carbon observation system (ICOS) network since 2017 (Rinne et al, 2018). Recently, Junninen et al (2022) performed a comprehensive observation in Siikaneva 1 to investigate oxidation products of monoterpene, clustering, and NPF.…”

“…Clearly, more emission studies on the larger terpene families are warranted, given their chemical diversities and important roles in NPF and SOA formation (Luo et al, 2021). Rose et al (2018) indicated the importance of clustering of pure biogenic molecules to contribute during nighttime in the boreal environment, and recently Junninen et al (2022) have found that high monoterpene emissions and their subsequent oxidation will cause atmospheric clustering and new particle formation (NPF) in the wetland environment of Siikaneva, southern Finland.…”

Nitrate radicals suppress biogenic new particle formation from monoterpene oxidation

“…Further, concentrations of CHO monomer and CHO dimer were 4 and 10 times higher than those of CHON monomer and CHON dimer during the NPF event, respectively, with total CHO species representing 80% of total OVOCs. In contrast, sharp increases of CHON monomer and CHON dimer were observed only during the nonevent when no decoupling process occurred but in well-mixed conditions with the rest of the atmosphere 52 . The presence of CHON dimer, which are markers for NO 3 chemistry, indicates the presence of NO 3 during the nonevent night 29,52 , which was estimated at nearly 1 ppqv, resulting in a reactivity of monoterpene 0.2 pptv h − 1 during the nonevent night (NO 2 :O 3 ≈ 0.007:1) with the reactivity of monoterpenes by NO 3 radicals in Siikaneva mainly coming from α-pinene (Supplementary Fig.…”