Relating high ozone, ultrafine particles, and new particle formation episodes using cluster analysis

Cristina Carnerero,Andrés Alastuey,Tiia M Laurila,Xavier Querol,Jenni Kontkanen,Kang-Ho Ahn,Tuukka Petäjä,Noemí Pérez,Lauri R Ahonen

doi:10.1016/j.aeaoa.2019.100051

Abstract

We studied the simultaneity of tropospheric ozone (O3) episodes, high ultrafine particle (UFP; diameter < 100 nm) concentrations, and the occurrence of new particle formation at a regional background station in the Western Mediterranean (northeast Spain), which is affected considerably by the transport of pollutants emitted in the Barcelona metropolitan area and nearby populated and industrial areas. Using cluster analysis, we categorized summer and spring days between 2014 and 2018 according to their daily cycles of O3 concentrations, and then studied the evolution of the particle number size distribution, meteorological variables, and black carbon and sulfur dioxide concentrations. The analysis revealed that, in spring and summer, the highest UFP concentrations coincided with the highest O3 episodes, but new particle formation was largely inhibited during these episodes, probably due to the high aerosol pollution load transported from the Barcelona metropolitan area to the station. In contrast, new particle formation episodes were concurrent with the lowest concentrations of O3 and UFPs, including the number of particles in the 9–25 nm size range. Measurements carried out in an intensive field study, using an air ion spectrometer and a particle size magnifier, support these results. In addition, measurements obtained onboard tethered balloons revealed that sea and land breezes transported regional pollutants vertically up to about 400 m above ground level. This coincided with episodes of vertical recirculation of air masses that lasted for several days, which resulted in high O3 and high UFP episodes, while new particle formation was inhibited.

Highlights

Ultrafine particles (UFPs; particles less than 100 nm in diameter) are not included in air quality regulations, but they have considerable po tential for affecting health (Atkinson et al, 2010; Lanzinger et al, 2016; Stafoggia et al, 2017; Tobías et al, 2018)
We use the term UFP episodes to designate the periods when number concentration markedly increases over the regional background particle number concentration (2000–3000 cm 3). These episodes may be caused by new particle formation bursts or by regional transport of air masses and plumes polluted with UFP particles
To understand the interconnections at a deeper level, in this study we focus on the warm seasons in the period 2014–2018 to investigate the relationship between episodes of O3, UFPs, and new particle formation (NPF) in the northern region of the Barcelona Province, where these episodes occurred with a relatively high frequency

Summary

Introduction

Ultrafine particles (UFPs; particles less than 100 nm in diameter) are not included in air quality regulations, but they have considerable po tential for affecting health (Atkinson et al, 2010; Lanzinger et al, 2016; Stafoggia et al, 2017; Tobías et al, 2018). Photochemical formation of new particles may exert a large influence on ambient levels of UFPs in urban and regional environments (Dall’Osto et al, 2013; Salma et al., 2016; Kerminen et al, 2018; Chu et al, 2019), and even dominate the total particle number concentrations at a global scale (Gordon et al, 2017). We use the term UFP episodes to designate the periods when number concentration (not necessarily particulate matter mass) markedly increases over the (usually low) regional background particle number concentration (2000–3000 cm 3). These episodes may be caused by new particle formation bursts or by regional transport of air masses and plumes polluted with UFP particles

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Results