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Abstract: Long range transport of dust originating from Arabian and African Deserts causes the transformations in the morphology and chemical composition of aerosols. Changes result from physical and chemical reactions occurring in the bulk or at the surface of single particles. Being an urban Mediterranean city, Beirut is subject to dust outbreaks from two desert sources between fall and summer seasons and hence, presents a typical case study of urban mixing with dust aerosols. In this study, particles collected during dust-rich episodes help to elucidate the different sources of long range transported aerosols. Elemental composition when coupled with specific morphological structures of single particles serves as markers to differentiate between these sources. [Copyright &y& Elsevier]

The accurate measurement of aerosol particles and clusters smaller than 3 nm in diameter is crucial for the understanding of new particle formation processes. The particle counters used for measuring these particles are typically calibrated with metal or salt particles under dry conditions, which does not always represent the field conditions where these instruments are later used. In this study, we calibrated the A11 nano Condensation Nucleus Counter (nCNC), consisting of the PSM (Particle Size Magnifier) and a laminar flow butanol based CPC (Condensational Particle Counter), with well-defined biogenic oxidation products from β-caryophyllene oxidation and compared it to a calibration with tungsten oxide under the same conditions. The organic particles were detected less efficiently than the inorganic ones. This resulted in a higher cut-off size for β-caryophyllene oxidation products than for tungsten oxide. At the same PSM settings, the cut-off size for tungsten oxide was 1.2 nm and for β-caryophyllene oxidation products 1.9 nm. However, repeating the calibration of the biogenic particles at 13% relative humidity at 31°C, increased their detection efficiency in the PSM, increasing the cut-off diameter to 1.6 nm. Additionally, we present a comparison of the ion concentrations measured with the PSM and the NAIS (Neutral Cluster and Air Ion Spectrometer) during new particle formation experiments in the CLOUD (Cosmics Leaving Outdoors Droplets) chamber. In these experiments, we produced particles from different organic precursors, such as α-pinene, β-caryophyllene and isoprene, as well as iodine. This way, we could determine the shift in cut-off diameter of the PSM for several different atmospherically relevant chemical compounds and compare it to the laboratory calibrations. We saw a diameter shift for the organic precursors of +0.3 nm in the PSM compared to the NAIS. These two approaches agreed well with each other and show that it is important to know the chemical composition of the measured particles to determine the exact size distribution using a supersaturation scanning method. • Accurate measurements of sub-3 nm particles are vital for the understanding of nucleation. • Organic particles are not as well detected by CPCs than inorganic ones. • Detection Efficiency of particle counters increases with increasing humidity. [ABSTRACT FROM AUTHOR]

The article reports about how Atmospheric new-particle formation (NPF) affects climate by contributing to a large fraction of the cloud condensation nuclei (CCN). Topics include how highly oxygenated organic molecules (HOMs) drive the early particle growth and therefore substantially influence the survival of newly formed particles to CCN; and how Nitrogen oxide (NOx) is known to suppress the NPF driven by HOMs, but the underlying mechanism remains largely unclear.

Measurements of aerosol particles and clusters smaller than 3 nm in diameter are performed by many groups in order to detect recently formed or emitted nanoparticles and for studying the formation and early growth processes of aerosol particles. The Airmodus nano-Condensation Nucleus Counter (nCNC), consisting of a Particle Size Magnifier (PSM) and a Condensation Particle Counter (CPC) is a versatile tool to detect aerosol particles and clusters as small as ca. 1 nm in mobility diameter. It offers several different operation modes: fixed mode to measure the total particle number concentration with a fixed, but adjustable lower cut-off size and stepping and scanning modes for retrieving size-resolved information of ca. 1–4 nm particles. The size analysis is based on changing the supersaturation of the working fluid (diethylene glycol) inside the instrument, which changes the lowest detectable size. Here we present a standard operating procedure (SOP) for setting up, calibrating and operating the instrument for atmospheric field measurements. We will also present recommendations for data monitoring and analysis, and discuss some of the uncertainties related to the measurements. This procedure is the first step in harmonizing the use of the PSM/nCNC for atmospheric field measurements of sub-3 nm clusters and particles. • A standard operating procedure (SOP) for Airmodus PSM and nCNC was developed. • It describes how to calibrate, set-up and operate the instrument. • The SOP is a step towards harmonizing the measurement of sub-3nm particles. [ABSTRACT FROM AUTHOR]

In this study, we propose a new approach to determine the contributions of primary vehicle exhaust (N 1 ff ), primary biomass burning (N 1 bb ) and secondary (N 2) particles to mode segregated particle number concentrations. We used simultaneous measurements of aerosol size distribution in the 12–600 nm size range and black carbon (BC) concentration obtained during winter period at urban and suburban sites influenced by biomass burning (BB) emissions. As expected, larger aerosol number concentrations in the 12–25 and 25–100 nm size ranges are observed at the urban site compared to the suburban site. However, similar concentrations of BC are observed at both sites due to the larger contribution of BB particles to the observed BC at suburban (34%) in comparison to urban site (23%). Due to this influence of BB emissions in our study area, the application of the Rodríguez and Cuevas (2007) method, which was developed for areas mainly influenced by traffic emissions, leads to an overestimation of the primary vehicle exhaust particles concentrations by 18% and 26% in urban and suburban sites, respectively, as compared to our new proposed approach. The results show that (1) N 2 is the main contributor in all size ranges at both sites, (2) N 1 ff is the main contributor to primary particles (>70%) in all size ranges at both sites and (3) N 1 bb contributes significantly to the primary particles in the 25–100 and 100–600 nm size ranges at the suburban (24% and 28%, respectively) and urban (13% and 20%, respectively) sites. At urban site, the N 1 ff contribution shows a slight increase with the increase of total particle concentration, reaching a contribution of up to 65% at high ambient aerosol concentrations. New particle formation events are an important aerosol source during summer noon hours but, on average, these events do not implicate a considerable contribution to urban particles. Unlabelled Image • New method to estimate contributions of primary and secondary particles is proposed. • Traffic primary emissions contribute up to 65% at high urban aerosol load. • Size-segregated particles from traffic and biomass burning sources are investigated. • Biomass burning emissions significantly contribute to primary particles. • New particle formation is an important source of particles during summer noon hours. [ABSTRACT FROM AUTHOR]