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Discussion papers
https://doi.org/10.5194/acp-2018-1357
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1357
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Feb 2019

Research article | 20 Feb 2019

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

New particle formation, growth and shrinkage at a rural background site in western Saudi Arabia

Simo Hakala1, Mansour A. Alghamdi2, Pauli Paasonen1, Mamdouh Khoder2, Kimmo Neitola3, Ville Vakkari3,4, Anu-Maija Sundström3, Jenni Kontkanen1, Ahmad S. Abdelmaksoud2, Hisham Al-Jeelani2, Heikki Lihavainen3,5, Tareq Hussein1, Markku Kulmala1,6, Veli-Matti Kerminen1, Antti-Pekka Hyvärinen3, Ibrahim I. Shabbaj2, and Fahd M. Almehmadi2 Simo Hakala et al.
  • 1Institute for Atmospheric and Earth System Research (INAR) /Physics, Faculty of Science, University of Helsinki, Finland
  • 2Department of Environmental Sciences, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia
  • 3Finnish Meteorological Institute, Helsinki, Finland
  • 4Unit for Environmental Sciences and Management, North-West University, ZA-2520 Potchefstroom, South Africa
  • 5Svalbard Integrated Arctic Earth Observing System (SIOS), Longyearbyen, Norway
  • 6Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, China

Abstract. Atmospheric aerosols have significant effects on human health and the climate. A large fraction of these aerosols originates from secondary new particle formation (NPF), where atmospheric vapors form small particles that subsequently grow into larger sizes. In this study, we characterize NPF events observed at a rural background site of Hada Al Sham (21.802° N, 39.729° E), located in western Saudi-Arabia, during the years 2013–2015. Our analysis shows that NPF events occur very frequently at the site, as 73 % of all the 454 classified days were NPF days. The high NPF frequency is likely 20 explained by the typically prevailing conditions of clear skies and high solar radiation, in combination with sufficient amounts of precursor vapors for particle formation and growth. In Hada Al Sham, the precursor vapors seem to be related to the transport of anthropogenic emissions from the coastal urban and industrial areas, since no NPF events are observed in air masses coming from the sparsely inhabited inland. The median particle formation and growth rates for the NPF days were 8.7 cm−3 s−1 (J7nm) and 7.4 nm h−1 (GR7–12nm), respectively, both showing highest values during late summer. In addition, the 25 formation and growth rates increase as a function of the condensation sink, likely reflecting the common anthropogenic sources of large primary particles and NPF precursor vapors. 76 % of the NPF days showed an unusual progression, where the observed diameter of the newly formed particle mode started to decrease after the growth phase. In comparison to most long-term measurements, the NPF events in Hada Al Sham are exceptionally frequent and strong. In addition, the frequency of the decreasing mode diameter events is higher than anywhere else in the world.

Simo Hakala et al.
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Short summary
Atmospheric aerosols have significant effects on human health and the climate. A large fraction of these aerosols originates from new particle formation, where atmospheric vapors form small nano-sized particles that grow into larger sizes, thus becoming climatically relevant. We show that large amounts of fast-growing particles are formed frequently at a site located in western Saudi-Arabia, and that these particles are connected to strong nearby emissions from human activities.
Atmospheric aerosols have significant effects on human health and the climate. A large fraction...
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