Measurement report: Long-term measurements of aerosol precursor concentrations in the Finnish subarctic boreal forest

Abstract

Abstract. Aerosol particles form in the atmosphere via the clustering of certain atmospheric vapors. After growing into larger particles by the condensation of low-volatility gases, they can affect the Earth's climate by scattering light and acting as cloud condensation nuclei (CCN). Observations of low-volatility aerosol precursor gases have been reported around the world, but longer-term measurement series and any Arctic data sets showing seasonal variation are close to nonexistent. Here, we present ∼7 months of aerosol precursor gas measurements performed with a nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer. We deployed our measurements ∼150 km north of the Arctic Circle at the SMEAR I (Station for Measuring Ecosystem–Atmosphere Relations) continental Finnish subarctic field station, located in the Värriö strict nature reserve. We report concentration measurements of the most common compounds related to new particle formation (NPF): sulfuric acid (SA), methane sulfonic acid (MSA), iodic acid (IA) and the total concentration of highly oxygenated organic molecules (HOMs). At this remote measurement site, SA originates from both anthropogenic and biological sources and has a clear diurnal cycle but no significant seasonal variation. MSA shows a more distinct seasonal cycle, with concentrations peaking in the summer. Of the measured compounds, IA concentrations are the most stable throughout the measurement period, except in April during which time the concentration of IA is significantly higher than during the rest of the year. Otherwise, IA has almost identical daily maximum concentrations in spring, summer and autumn, and on NPF event or non-event days. HOMs are abundant during the summer months and low in the autumn months. Due to their low autumn concentrations and high correlation with ambient air temperature, we suggest that most HOMs are products of biogenic emissions, most probably monoterpene oxidation products. NPF events at SMEAR I happen under relatively low-temperature (1–8 ∘C) conditions, with a fast temperature rise in the early morning hours as well as lower and decreasing relative humidity (RH, 55 % vs. 80 %) during NPF days compared with non-event days. NPF days have clearly higher global irradiance values (∼450 m−2 vs. ∼200 m−2) and about 10 ppbv higher ozone concentrations than non-event days. During NPF days, we have, on average, higher SA concentrations, peaking at noon; higher MSA concentrations in the afternoon; and slightly higher IA concentration than during non-event days. In summary, these are the first long-term measurements of aerosol-forming vapors from SMEAR I in the subarctic region, and the results of this work will help develop an understanding of atmospheric chemical processes and aerosol formation in the rapidly changing Arctic.

New particle formation in coastal New Zealand with a focus on open-ocean air masses

“…The daytime increase can be explained by sunny conditions warming the air during the day. This trend is similar to what Jokinen et al (2022) observed in northern Finland.…”

Iodine oxoacids and their roles in sub-3 nanometer particle growth in polluted urban environments

“…As for the two iodine oxoacids (HIO3 and HIO2), daytime mean concentration of HIO3 is more than one order of magnitude higher than HIO2. The one order of magnitude lower HIO3 concentration compared with H2SO4 in summer at both sites is consistent with that in the Finnish subarctic boreal forest (Jokinen et al, 2022).…”

“…On the other hand, HIO3 concentrations in Beijing and Nanjing are comparable to that in Helsinki, Finland. Measurements at SMEAR III station, an urban site located in University of Helsinki show HIO3 concentrations at around 10 6 cm -3 when the wind is coming from land for most times in August and HIO3 concentrations exceed 365 10 7 cm -3 when air masses have marine origin (Thakur et al, 2022;He et al, 2021b). Another long-term observation conducted at SMEAR I station (Jokinen et al, 2022), a subarctic boreal forest site, shows HIO3 concentrations often at around 10 5 cm -3 from April to November 2019 (summer and autumn) with occasional peaks exceeding 10 6 cm -3 in late August.…”

“…However, field observations at the Mace Head observatory and dedicated experiments carried out in the CLOUD chamber at CERN revealed iodine oxoacids (HIOx,i.e.,HIO3 and HIO2 in this study) as the key nucleating species in pristine regions (Zhang et al, 2022;He et al, 2021b). With state-80 of-the-art mass spectrometric methods, iodine oxoacids were recently identified in locations other than mid-latitude costal sites, such as in Arctic sites (Sipilä et al, 2016;Baccarini et al, 2020;Beck et al, 2021;He et al, 2021b), Antarctica sites (Jokinen et al, 2018;He et al, 2021b), boreal forest sites (Jokinen et al, 2022;He et al, 2021b), a remote marine site (He et al, 2021b) and importantly also in polluted urban sites (He et al, 2021b). Chamber experiments have shown that HIO3 (with HIO2) 85 nucleates faster than H2SO4 with 100 pptv NH3 at the same temperature and equal acid concentrations, although iodine oxoacid nucleation rates are still lower than H2SO4-DMA nucleation (He et al, 2021b).…”

Characterization of ultrafine particles and the occurrence of new particle formation events in an urban and coastal site of the Mediterranean area

“…The formation of new particles was observed and investigated in various geographic locations under different atmospheric and environmental conditions, from which common characteristics and different peculiarities emerged (Baalbaki et al, 2021;Jokinen et al, 2022;Yadav et al, 2021;Franco et al, 2022).…”