Diurnal evolution of negative atmospheric ions above the boreal forest: From ground level to the free troposphere

Abstract

Abstract. At SMEAR II research station in Hyytiälä, located in the Finnish boreal forest, the process of new particle formation and the role of ions has been investigated for almost 20 years near the ground and at canopy level. However, above SMEAR II, the vertical distribution and diurnal variation of these different atmospheric ions are poorly characterized. In this study, we assess the atmospheric ion composition in the stable boundary layer, residual layer, mixing layer and free troposphere, and the 5 evolution of these atmospheric ions due to photochemistry and turbulent mixing through the day. To measure the vertical profile of atmospheric ions, we developed a tailored setup for online mass spectrometric measurements, capable of being deployed in a Cessna 172 with minimal modifications. Simultaneously, instruments dedicated to aerosol properties measured in a second Cessna. We conducted a total of 16 measurement flights in May 2017, during the spring, which is the most active new particle formation season. A flight day typically consisted of three distinct flights through the day (dawn, morning and afternoon) to 10 observe the diurnal variation and at different altitudes (from 100 m to 3200 m above ground), and to capture the boundary layer development from stable boundary layer, residual layer to mixing layer, and the free troposphere. Our observations showed that the ion composition is distinctly different in each layer and depends on the air mass origin and time of the day. Before sunrise, the layers are separated from each other and have their own ion chemistry. We observed that the ions present within the stable layer are of the same composition as the ions measured at the canopy level. During daytime when the mixing layer evolved and the compounds are vertically mixed, we observed that highly oxidised organic molecules are distributed to the top of the boundary layer. The ion composition in the residual layer varies with each day, showing similarities with either the stable boundary layer or the free troposphere. Finally, within the free troposphere, we detected a variety of carboxylic acids and ions that are likely containing halogens, originating from the Arctic Sea.

Chemical identification of new particle formation and growth precursors through positive matrix factorization of ambient ion measurements

“…S3). The dominance of sulfuric acid in the daytime spectra is expected based on photochemical production of sulfuric acid, competition for limited charges available in the ambient atmosphere, and the strong acidity of sulfuric acid and is consistent with previous observations (e.g., (Eisele and Tanner, 1990;Ehn et al, 2010;Bianchi et al, 2017;Beck et al, 2022).…”

“…Therefore, anions are commonly derived from strong acids such as nitric acid and sulfuric acid (Perkins and Eisele, 1984;Eisele and Tanner, 1990;Eisele, 1988). Highly oxygenated molecules (HOMs) derived from monoterpenes (MTs) have frequently been observed clustered with sulfate or nitrate anions (Ehn et al, 2010(Ehn et al, , 2012Bianchi et al, 2017;Beck et al, 2022). In the boreal forest, HOMs derived from sesquiterpenes have also been observed as naturally charged clusters (Jokinen et al, 2016).…”

Diurnal evolution of negative atmospheric ions above the boreal forest: from ground level to the free troposphere

“…Data availability. The APi-TOF and airborne data are available on Zenodo with https://doi.org/10.5281/zenodo.6619318 (Beck et al, 2021b). The SMEAR II data can be accessed from https://smear.…”

Mass spectrometric measurements of ambient ions and estimation of gaseous sulfuric acid in the free troposphere and lowermost stratosphere during the CAFE-EU/BLUESKY campaign

“…For most of the troposphere and stratosphere, only sulfuric acid (H 2 SO 4 ) fulfils this requirement while being sufficiently abundant (Viggiano and Arnold, 1995). It is only closer to the ground that strong and abundant acids such as malonic acid (CH 2 (COOH) 2 ), methanesulfonic acid (CH 3 SO 3 H), or iodic acid (HIO 3 ) can also be observed as part of the ion clusters (Ehn et al, 2010;Eisele, 1989a;Frege et al, 2017;Viggiano and Arnold, 1995;He et al, 2021;Beck et al, 2022a). It should be noted that, practically, the only source for HSO − 4 ions and their ion clusters is the reaction of gaseous sulfuric acid with nitrate (clusters) (Viggiano and Arnold, 1995).…”

“…Positive ions were assigned to amines, ammonia, and organic clusters. More recently, Beck et al (2022a) conducted airborne measurements of ambient ions above the boreal forest at an altitude range of 0 to 3200 m around the Station for Measuring Ecosystem Atmospheric Relations (SMEAR) II in Hyytiälä. They identified ions belonging to nitric, iodic, methanesulfonic, sulfuric, and carboxylic acid, as well as highly oxygenated organic molecules (HOMs).…”