10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Observations of Biogenic New Particle Formation over a Boreal Fen
HEIKKI JUNNINEN, Lauri R. Ahonen, Federico Bianchi, Lauriane Quéléver, Simon Schallhart, Hanna Manninen, Katri Leino, Janne Lampilahti, Stephany Mazon, Jenni Kontkanen, Pavel Alekseychik, Janne Levula, Ivan Mammarella, Timo Vesala, Tuukka Petäjä, Markku Kulmala, University of Tartu
Abstract Number: 459 Working Group: Aerosol Chemistry
Abstract Formation of new aerosol particles in the atmosphere is a complicated series of chain reactions, including the production of nanometre-size clusters from precursor vapours, the growth of these clusters to detectable sizes by condensation and the simultaneous removal of clusters by coagulation. It is thought that sulphuric acid is critical in initialization of the particle formation, except in certain coastal regions where iodine oxides are dominating the process. Recent laboratory studies hypothesise that pure organic ion-induced new particle formation could potentially happen also in atmospherically relevant conditions.
In this study, we measured the composition of biogenic volatile organic compounds (BVOC) emissions from a wetland, depletion of O3 and formation of the oxidation products of emitted BVOCs. We also show the involvement of produced low volatile organic compounds in atmospheric new particle formation.
The measurement campaign was conducted in a boreal wetland close to the Station for Measuring Ecosystem-Atmosphere Relations II (SMEAR II). The vegetation of the site is dominated by different sedges and a continuous Sphagnum carpet. The fen acts as a source of methane throughout the year with the maximum during the summer time and minimum during the coldest season. The CO2 fluxes in contrary have a negative annual balance -156 g m-2, equals -42.5 g-C m-2.
The site is equipped with permanent measurements for basic meteorology and for CO2, H2O, and CH4 fluxes. Additionally, the chemical composition of atmospheric ions was measured with atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF), concentrations of sulfuric acid (SA) and low volatile oxygenated organics (highly oxidized multifunctional molecules, HOM) with chemical ionization with nitrate chemistry (NO3-CI)-APi-TOF. Volatile organic compounds (VOC) were measured with proton transfer reaction (PTR)-TOF. Atmospheric cluster and aerosol size distribution was measured with Neutral clusters and Air Ion Spectrometer (NAIS) and nano-particles.
During the campaign, we observed several new particle formation events. The events observed during the day time (NPFd) had the same characteristics as the ones observed in forest station, 10 km away. During NPFd the sulphuric acid was the one single most increasing component. However, during the night time events (NPFn) the observed chemistry was considerably different. The most prominent difference was the decrease of O3 concentration to as low levels as 2-5 ppb. At the same time the concentrations of nitrogen containing HOMs increased by an order of magnitude, but non-nitrogen containing HOMs decreased. This behaviour points towards a purely organic oxidation and formation of new particulates, without involvement of SA.
These events became more frequent after the snow melt and the increased temperature difference between day and night. Low relative humidity and low wind speeds are also associated with the observed night time organic new particle formation events.
In the presentation observed organic oxidation and consecutive new particle formation will be discussed in details.
This work is supported by the Academy of Finland Centre of Excellence (grant no. 272041), the European Union’s Horizon 2020 research and innovation program (grant No 654109), European Research Council (ERC-StG COALA), European Regional Development Fund and Estonian Research Council programme Mobilitas Pluss project MOBTT42 and we thank the tofTools team for providing tools for mass spectrometry analysis.