Study of the hygroscopic properties of atmospheric aerosol and the effect of the variation of organic and elemental carbon on the aerosol of Attica and the wider environment of the Eastern Mediterranean

The hygroscopic properties of atmospheric aerosol were investigated at a suburban environment in Athens, Greece, from August 2016 to July 2017. The Growth Factor Distribution Probability Density Function, (GF-PDF), and mixing state were determined with a Hygroscopicity Tandem Differential Mobility Analyzer, (HTDMA). Four dry particle sizes, (D0), were selected to be analyzed in terms of their hygroscopic properties at 90 % relative humidity. The annual mean GFs for D0 =30 nm, 50 nm, 80 nm and 250 nm, were found to be equal to 1.28, 1.11, 1.13 and 1.22, respectively. The hygroscopic growth spectra were divided into two distinct hygroscopic ranges; a non and/or slightly hygroscopic mode (GF˂1.12) and a moderately hygroscopic mode (GF˃1.12), which are representative of a suburban environment influenced by local/urban emissions and background aerosol. The standard deviation σ of the GF-PDF was employed as a measure of the mixing state of ambient aerosol. Cluster analysis on the hourly dry number size distributions, was performed to identify the link between aerosol hygroscopicity and aerosol emission sources and formation processes. In addition, was conducted the prediction of Cloud Condensation Nuclei (CCN), number concentrations based on 12 months time- and size-resolved HTDMA data and on the number size distributions at five supersaturations, from 0.05% to 0.70%, by using four different assumptions in order to examine how the different parameters affect the potential of particles to act as CCN. In addition, the role of Organic Carbon (OC), and Elemental Carbon (EC), in CCN activation was investigated, with the effect depedent on meteorological data.Οι υγροσκοπικές ιδιότητες του ατμοσφαιρικού αερολύματος, καθώς και επίδραση της χωροχρονικής διακύμανσης του οργανικού και στοιχειακού άνθρακα, διερευνήθηκαν από μετρήσεις που πραγματοποιήθηκαν στο σταθμό του , ο οποίος είναι αντιπροσωπευτικός του περι-αστικού περιβάλλοντος της Αττικής, δεχόμενος επιρροές από τον περιβάλλοντα αστικό ιστό, χρονοσειράς ενός έτους. Χρησιμοποιώντας την τεχνική του Αναλυτή Διαφορικής Ηλεκτρικής Κινητικότητας προσδιορίστηκαν οι συντελεστές μεγέθυνσης τεσσάρων μεγεθών ξηρών σωματιδίων, σε σχετική υγρασία 90%. Οι ετήσιες μέσες τιμές των συντελεστών μεγέθυνσης για τα σωματίδια διαμέτρων, D0 =30 nm, 50 nm, 80 nm και 250 nm, βρέθηκαν να είναι ίσοι με 1,28, 1,11, 1,13 και 1,22, αντίστοιχα. Τα υγροσκοπικά φάσματα του συντελεστή μεγέθυνσης χωρίστηκαν σε δύο διακριτά υγροσκοπικά εύρη, ένα μη και/ή ελαφρώς υγροσκοπικό (GF˂1,12) και ένα μετρίως υγροσκοπικό (GF˃1,12), τα οποία είναι αντιπροσωπευτικά ενός περι-αστικού περιβάλλοντος που επηρεάζεται από τοπικές/αστικές εκπομπές και του αερολύματος υποβάθρου. Η τυπική απόκλιση, σ, των συντελεστών μεγέθυνσης χρησιμοποιήθηκε ως μέτρο προσδιορισμού της κατάστασης ανάμειξης του αερολύματος. Επιπροσθέτως, πραγματοποιήθηκε ανάλυση συστάδων στις ωριαίες κατανομές μεγέθους των σωματιδίωνΕν συνεχεία, χρησιμοποιώντας τα δεδομένα του Αναλυτή Διαφορικής Ηλεκτρικής Κινητικότητας και τις αριθμητικές κατανομές μεγέθους των σωματιδίων, πραγματοποιήθηκε ο υπολογισμός των συγκεντρώσεων του αριθμού των σωματιδίων, τα οποία δύνανται να δράσουν ως πυρήνες συμπύκνωσης νεφών, σε πέντε διαφορετικούς υπερκορεσμούς, χρησιμοποιώντας 4 διαφορετικές προσεγγίσεις. Λαμβάνοντας υπόψιν την επίδραση του οργανικού κλάσματος και των μετεωρολογικών παραμέτρων, διερευνήθηκε η συμβολή του οργανικού και στοιχειακού άνθρακα και του δευτερογενούς οργανικού αερολύματος στον αριθμό των σωματιδίων που δύνανται να δράσουν ως πυρήνες συμπύκνωσης νεφών

PM_2.5 Source Apportionment and Implications for Particle Hygroscopicity at an Urban Background Site in Athens, Greece

Aerosol hygroscopicity is a key aerosol property, influencing a number of other physical properties, and the impacts of PM pollution on the environment, climate change, and health. The present work aims to provide insight into the contribution of major PM sources to aerosol hygroscopicity, focusing on an urban background site, with a significant impact from both primary and secondary sources. The EPA PMF 5.0 model was applied to PM2.5 chemical composition and hygroscopicity data collected from August 2016 to July 2017 in Athens, Greece. Source apportionment analysis resulted in six major sources, including four anthropogenic sources (vehicular exhaust and non-exhaust, heavy oil combustion, and a mixed source of secondary aerosol formation and biomass burning) and two natural sources (mineral dust and aged sea salt). The mixed source was found to be the main contributor to PM2.5 levels (44%), followed by heavy oil combustion (26%) and vehicular traffic exhaust and non-exhaust emissions (15%). The aerosol hygroscopic growth factor (GF) was found to be mainly associated with the mixed source (by 36%) and heavy oil combustion (by 24%) and, to a lesser extent, with vehicle exhaust (by 19%), aged sea salt (by 14%), and vehicle non-exhaust (by 6%)

Atmospheric chemistry of (CF 3 ) 2 CQ Q QCH 2 : OH radicals, Cl atoms and O 3 rate coefficients, oxidation end-products and IR spectra †

International audienceThe rate coefficients for the gas phase reactions of OH radicals, k 1 , Cl atoms, k 2 , and O 3 , k 3 , with 3,3,3-trifluoro-2(trifluoromethyl)-1-propene ((CF 3) 2 CQCH 2 , hexafluoroisobutylene, HFIB) were determined at room temperature and atmospheric pressure employing the relative rate method and using two atmospheric simulation chambers and a static photochemical reactor. OH and Cl rate coefficients obtained by both techniques were indistinguishable, within experimental precision, and the average values were k 1 = (7.82 AE 0.55) Â 10 À13 cm 3 molecule À1 s À1 and k 2 = (3.45 AE 0.24) Â 10 À11 cm 3 molecule À1 s À1 , respectively. The quoted uncertainties are at 95% level of confidence and include the estimated systematic uncertainties. An upper limit for the O 3 rate coefficient was determined to be k 3 o 9.0 Â 10 À22 cm 3 molecule À1 s À1. In global warming potential (GWP) calculations, radiative efficiency (RE) was determined from the measured IR absorption cross-sections and treating HFIB both as long (LLC) and short (SLC) lived compounds, including estimated lifetime dependent factors in the SLC case. The HFIB lifetime was estimated from kinetic measurements considering merely the OH reaction, t OH = 14.8 days and including both OH and Cl chemistry, t eff = 10.3 days. Therefore, GWP(HFIB,OH) and GWP(HFIB,eff) were estimated to be 4.1 (LLC) and 0.6 (SLC), as well as 2.8 (LLC) and 0.3 (SLC) for a hundred year time horizon. Moreover, the estimated photochemical ozone creation potential (e POCP) of HFIB was calculated to be 4.60. Finally, HCHO and (CF 3) 2 C(O) were identified as final oxidation products in both OH-and Cl-initiated oxidation, while HC(O)Cl was additionally observed in the Cl-initiated oxidation