Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Several studies have investigated new particle formation (NPF) events from various sites ranging from pristine locations, including forest sites, to urban areas. However, there is still a dearth of studies investigating NPF processes and subsequent aerosol growth in coastal yet semi-urban sites, where the tropospheric layer is a concoction of biogenic and anthropogenic gases and particles. The investigation of factors leading to NPF becomes extremely complex due to the highly dynamic meteorological conditions at the coastline especially when combined with both continental and oceanic weather conditions. Herein, we engage in a comprehensive study of particle number size distributions and aerosol-forming precursor vapors at the coastal semi-urban site in Helsinki, Finland. The measurement period, 25 June–18 August 2019, was timed with the recurring cyanobacterial summer bloom in the Baltic Sea region and coastal regions of Finland. Our study recorded several regional/local NPF and aerosol burst events during this period. Although the overall anthropogenic influence on sulfuric acid (SA) concentrations was low during the measurement period, we observed that the regional or local NPF events, characterized by SA concentrations on the order of <span class="inline-formula">10<sup>7</sup></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">molec</mi><mo>.</mo><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">cm</mi><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="60pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="2c6d3fde5a2cf89a9afa70db0a81e460"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-6365-2022-ie00001.svg" width="60pt" height="13pt" src="acp-22-6365-2022-ie00001.png"/></svg:svg></span></span>, occurred mostly when the air mass traveled over the land areas. Interestingly, when the air mass traveled over the Baltic Sea, an area enriched with algae and cyanobacterial blooms, high iodic acid (IA) concentration coincided with an aerosol burst or a spike event at the measurement site. Further, SA-rich bursts were seen when the air mass traveled over the Gulf of Bothnia, enriched with cyanobacterial blooms. The two most important factors affecting aerosol precursor vapor concentrations, and thus the aerosol formation, were speculated to be (1) the type of phytoplankton species and intensity of bloom present in the coastal regions of Finland and the Baltic Sea and (2) the wind direction. During the events, most of the growth of sub-3 nm particles was probably due to SA, rather than IA or methane sulfonic acid (MSA); however much of the particle growth remained unexplained indicative of the strong role of organics in the growth of particles, especially in the 3–7 nm particle size range. Further studies are needed to explore the role of organics in NPF events and the potential influence of cyanobacterial blooms in coastal locations.

Highlights

  • New particle formation (NPF) and growth of aerosols are regional processes occurring globally introducing a substantial aerosol load into the atmosphere

  • The source of precursor gases causing new particle formations were assessed by analyzing the meteorological parameters, situation of cyanobacterial bloom in the Baltic Sea

  • Our study recorded several regional, local and burst events and we found that they were connected to elevated concentrations of SA and Iodic Acid (IA)

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Summary

Introduction

New particle formation (NPF) and growth of aerosols are regional processes occurring globally introducing a substantial aerosol load into the atmosphere. Amines-water yield much higher nucleation rates as compared to the binary system (Kulmala et al., 2000; Benson et al, 2008; Almeida et al, 2013; Glasoe et al, 2015; Kürten et al, 2016) In addition to these systems, organic compounds which are highly oxygenated - less volatile- have been found to contribute to secondary organic aerosol (SOA) mass in forested areas, mountain tops and anthropogenically influenced field sites (Ehn et al, 2014; Pierce et al, 2011; Riipinen et al, 2012; Zhang et al, 2009; Heikkinen et al 2020; et al, 2020) and laboratory experiments have shown that they can contribute to the first steps of NPF (Simon et al, 2020; Lehtipalo et al, 2018; Kirkby et al, 2016; Tröstl et al, 2016). The increase in frequency and intensity of cyanobacterial blooms would increase the potential emission of biogenic gases changing the composition of the overlying atmosphere and the atmosphere of the neighboring sites, depending on the meteorological conditions

Main Instruments
Back trajectory calculations
Meteorological and other supporting data
Formation and growth rate calculations
Condensation sink
Meteorological Parameters
Cyanobacterial bloom conditions during the study
Precursor vapor concentrations and their sources
Types of nucleation events during the study
Nucleation
Possible contributions of biogenic emissions to Precursor gaseous vapors
Conclusions

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