Long-term measurement of sub-3 nm particles and their precursor gases in the boreal forest

Juha Sulo,Heikki Junninen,Juha Kangasluoma,Nina Sarnela,Pauli Paasonen,Lauri Ahonen,Katrianne Lehtipalo,Jenni Kontkanen,Tiia Laurila,Tuukka Petäjä,Mikko Sipilä,Markku Kulmala,Tuija Jokinen

doi:10.5194/acp-21-695-2021

Abstract

Abstract. The knowledge of the dynamics of sub-3 nm particles in the atmosphere is crucial for our understanding of the first steps of atmospheric new particle formation. Therefore, accurate and stable long-term measurements of the smallest atmospheric particles are needed. In this study, we analyzed over 5 years of particle concentrations in size classes 1.1–1.7 and 1.7–2.5 nm obtained with the particle size magnifier (PSM) and 3 years of precursor vapor concentrations measured with the chemical ionization atmospheric pressure interface time-of-flight mass spectrometer (CI-APi-ToF) at the SMEAR II station in Hyytiälä, Finland. The results show that there are significant seasonal differences in median concentrations of sub-3 nm particles, but the two size classes behave partly differently. The 1.1–1.7 nm particle concentrations are highest in summer, while the 1.7–2.5 nm particle concentrations are highest in springtime. The 1.7–2.5 nm particles exhibit a daytime maximum in all seasons, while the 1.1–1.7 nm particles have an additional evening maximum during spring and summer. Aerosol precursor vapors have notable diurnal and seasonal differences as well. Sulfuric acid and highly oxygenated organic molecule (HOM) monomer concentrations have clear daytime maxima, while HOM dimers have their maxima during the night. HOM concentrations for both monomers and dimers are the highest during summer and the lowest during winter following the biogenic activity in the surrounding forest. Sulfuric acid concentrations are the highest during spring and summer, with autumn and winter concentrations being 2 to 3 times lower. A correlation analysis between the sub-3 nm concentrations and aerosol precursor vapor concentrations indicates that both HOMs (particularly their dimers) and sulfuric acid play a significant role in new particle formation in the boreal forest. Our analysis also suggests that there might be seasonal differences in new particle formation pathways that need to be investigated further.

Highlights

Atmospheric aerosols are one of the largest sources of uncertainty in climate models
We present the 74 month time series of sub-3 nm particle concentrations and the 31 month time series of aerosol precursor vapors measured at the SMEAR II station in Hyytiälä, southern Finland, and their comparison for the overlapping time period
The sub-3 nm particle concentrations were measured with the particle size magnifier (PSM),and the aerosol precursor molecule concentration data were measured with the CI-APi-ToF

Summary

Introduction

Atmospheric aerosols are one of the largest sources of uncertainty in climate models. To diminish these uncertainties, it is vital to understand the sources and formation pathways of aerosol particles. New particle formation (NPF) in the atmosphere has been observed to occur in various environments (Kulmala et al, 2004; Kerminen et al, 2018, and references therein) from megacities (Hofman et al, 2016; Wu et al, 2007; Qi et al, 2015) rainforests (Wimmer et al, 2018; Andreae et al, 2018), rural areas (Mäkelä et al, 1997; Vakkari et al, 2011; Heintzenberg et al, 2017; Nieminen et al, 2014), and even polar areas (Weller et al, 2015; Kyrö et al, 2013; Järvinen et al, 2013; Sipilä et al, 2016). Aerosol particles have been observed to form through various pathways involving different chemical compounds and ions (e.g., Kirkby et al, 2016; Lehtipalo et al, 2018). Sulo et al.: Long-term measurement of sub-3 nm particles and their precursor gases

Methods

Results

Conclusion