Investigating New Particle Formation and Growth Over an Urban Location in the Eastern Mediterranean

This study investigates the new particle formation (NPF) events at an urban location in the Eastern Mediterranean. Particle size distribution, particulate chemical composition, and gaseous pollutants were monitored in Rehovot, Israel (31°53″N 34°48″E) during two campaigns: from April 29 to 3 May 2021 (Campaign 1) and from May 3 to 11 May 2023 (Campaign 2), coinciding with an intensive bonfire burning festival. The organic aerosols (OA) source apportionment identified two major factors—Hydrocarbon-like OA and Biomass-burning OA—as well as two secondary factors—MO-OOA (more oxidized-oxygenated OA) and LO-OOA (low oxidized oxygenated OA). NPF events were frequently observed during the day (mostly well-defined nucleation events) and at night (burst of ultrafine mode particles without any discernible growth). A condensation sink value of (9.4 ± 4.0) × 10⁻³ s⁻¹ during Campaign 1 and (14.2 ± 6.0) × 10⁻³ s⁻¹ during Campaign 2 was obtained. The daytime events were associated with enhanced sulfuric acid proxy concentrations of (2–12) × 10⁶ molecules cm⁻³, suggesting the role of gas-phase photochemistry in promoting NPF. A novel approach of hybrid positive matrix factorization analysis was used to deconvolve the chemical species responsible for the observed events. The results suggest the involvement of multiple components, including ammonium sulfate and MO-OOA, in the nucleation; Nitrate, HOA and LO-OOA participate in the subsequent particle growth for the daytime events. Nighttime events involve only semi-volatile species (LO-OOA, HOA and nitrate) along with ammonium sulfate.