Towards understanding the mechanisms of new particle formation in the Eastern Mediterranean

Abstract

Abstract. To quantify the contribution of new particle formation (NPF) to ultrafine particle number and CCN budgets, one has to understand the mechanisms that govern NPF in different environments and its temporal extent. Here, we study NPF in Cyprus, an Eastern Mediterranean country located at the crossroads of three continents. We performed one-year continuous measurements of aerosol particles down to ~ 1 nm in diameter, for the first time in the Eastern Mediterranean and Middle East (EMME) region. These measurements were complemented with trace gas data, meteorological variables and retroplume analysis. We show that NPF is a very frequent phenomenon at this site and has higher frequencies of occurrence during spring and autumn. NPF events were both of local and regional origin, and the local events occurred frequently during the month with the lowest NPF frequency. Some NPF events exhibited multiple onsets, while others exhibited particle apparent shrinkage in size. Additionally, NPF events were observed during the night-time and during episodes of high desert dust loadings. Particle formation rates and growth rates were comparable to those in urban environments, although our site is a rural one. Meteorological variables and trace gases played a role in explaining the intra-monthly variability of NPF events, but did not explain why summer month had the least NPF frequency. Similarly, pre-existing aerosol loading did not explain the observed seasonality. The month with the least NPF frequency were associated with higher H2SO4 concentrations but lower NOx concentration, which is an indicator of anthropogenic influence. Air masses arriving from the Middle East were not observed during these month, which could suggest that precursor vapors important for nucleation and growth are transported to our site from the Middle East. Further comprehensive measurements of precursor vapors are required to prove this hypothesis.