Χημικός χαρακτηρισμός των λεπτόκοκκων σωματιδίων και εύρεση των πηγών των οργανικών αερολυμάτων απο μετρήσεις πεδίου και εργαστηριακά πειράματα

Atmospheric aerosols, also known as atmospheric particles, are suspended particles (solid or liquid) in the air with diameters ranging from 1 nm to about 100 μm. Atmospheric aerosols affect the Earth's radiant budget and hence the global climate through its so-called direct and indirect radioactive effects, and also have a negative impact on human health. They can be classified as primary (emitted directly into the particle phase) or secondary (formed in the atmosphere through a series of chemical reactions). Typically, atmospheric particles consist of a mixture of inorganic and organic chemicals, including nitrates, sulfates, ammonia, organic compounds, elemental carbon, sea salt, crystalline compounds and water. The organic aerosol represents a significant fraction of the mass of atmospheric particles, but its sources and chemical composition have not yet been elucidated. Real-time high resolution aerosol mass spectroscopy was the central measurement technique used in this work. The Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) can continuously measure the chemical composition and size distribution of non-refractory submicron aerosol (NR-PM1). The high-resolution mass spectra provided by the instrument every few minutes contain information about both the organic aerosol sources and processes. This thesis presents the first HR-ToF-AMS measurements in two major Greek cities (Athens and Patras) and a remote site (Finokalia, Crete) and quantifies the contributions of the various sources to the corresponding organic aerosol levels. In addition, the formation of secondary organic aerosol during the photo-oxidation of m- and p-xylene, two important atmospheric aromatic hydrocarbons, is investigated in the laboratory using an atmospheric simulation chamber.Τα ατμοσφαιρικά αερολύματα, γνωστά και ως ατμοσφαιρικά σωματίδια, είναι αιωρούμενα σωματίδια (στερεά ή υγρά) στον αέρα με διαμέτρους που κυμαίνονται από 1 nm έως περίπου 100 μm. Το ατμοσφαιρικά αερολύματα επηρεάζουν τον ακτινοβόλο προϋπολογισμό της Γης και συνεπώς το παγκόσμιο κλίμα μέσω των αποκαλούμενων άμεσων και έμμεσων ραδιενεργών επιδράσεων τους, ενώ έχουν επίσης αρνητικές επιπτώσεις στην ανθρώπινη υγεία. Μπορούν να ταξινομηθούν ως πρωτογενή (εκπεμπόμενα απευθείας στη φάση των σωματιδίων) ή δευτερογενή (σχηματίζονται στην ατμόσφαιρα μέσω μιας σειράς χημικών αντιδράσεων). Συνήθως, τα ατμοσφαιρικά σωματίδια αποτελούνται από ένα μείγμα ανόργανων και οργανικών χημικών ειδών, συμπεριλαμβανομένων των νιτρικών, θειικών, αμμωνιακών, οργανικών ενώσεων, στοιχειακού άνθρακα, θαλάσσιου άλατος, κρυσταλλικών ενώσεων και νερού. Το οργανικό αερόλυμα αντιπροσωπεύει ένα σημαντικό κλάσμα της μάζας των ατμοσφαιρικών σωματιδίων, αλλά οι πηγές και η χημική του σύνθεση δεν έχουν διευκρινιστεί ακόμη. Η φασματομετρία μάζας υψηλής ανάλυσης σε πραγματικό χρόνο ήταν η κεντρική τεχνική μέτρησης που χρησιμοποιήθηκε σε αυτή την εργασία. Το φασματόμετρο μάζας αερολύματος υψηλής ανάλυσης (HR-ToF-AMS) έχει τη δυνατότητα να μετρά συνεχώς τη χημική σύνθεση και την κατανομή μεγέθους των λεπτόκοκκων σωματιδίων (αεροζόλ με διάμετρο μικρότερη του 1μm). Τα φάσματα μάζας υψηλής ανάλυσης που παρέχονται από το όργανο κάθε λίγα λεπτά περιέχουν πληροφορίες τόσο για τις πηγές του οργανικού αεροζόλ όσο και για τη χημική του σύνθεση. Η εργασία αυτή παρουσιάζει τις πρώτες μετρήσεις με τη χρήση του HR-ToF-AMS σε δύο μεγάλες πόλεις της Ελλάδας (Αθήνα και Πάτρα) καθώς και σε μια απομακρυσμένη περιοχή (Φινοκαλιά, Κρήτη) και μελετάται η συμβολή των διαφόρων πηγών στα αντίστοιχα επίπεδα του οργανικού αεροζόλ. Επιπλέον, ο σχηματισμός δευτερογενούς οργανικού αερολύματος (SOA) κατά τη διάρκεια της φωτο-οξείδωσης του m- και p-ξυλένιου, δύο σημαντικών αρωματικών υδρογονανθράκων, διερευνάται στο εργαστήριο χρησιμοποιώντας έναν ατμοσφαιρικό θάλαμο προσομοίωσης

Development and evaluation of an improved offline aerosol mass spectrometry technique

Abstract. The offline aerosol mass spectrometry technique is a useful tool for the source apportionment of organic aerosol (OA) in areas and periods during which an aerosol mass spectrometer (AMS) is not available. However, the technique is based on the extraction of aerosol samples in water, while several atmospheric OA components are partially or fully insoluble in water. In this work an improved offline technique was developed and evaluated in an effort to capture most of the partially soluble and insoluble organic aerosol material, reducing significantly the uncertainty of the corresponding source apportionment. A major advantage of the proposed approach is that no corrections are needed for the offline analysis to account for the limited water solubility of some OA components. The improved offline AMS analysis was tested in three campaigns: two during winter and one during summer. Collocated online AMS measurements were performed for the evaluation of the offline method. Source apportionment analysis was performed separately for the online and the offline measurements using positive matrix factorization (PMF). The PMF results showed that the fractional contribution of each factor to the total OA differed between the online and the offline PMF results by less than 15 %. The differences in the AMS spectra of the factors of the two approaches could be significant, suggesting that the use of factor profiles from the literature in the offline analysis may lead to complications. Part of the good agreement between the online and the offline PMF results is due to the ability of the improved offline AMS technique to capture a bigger part of the OA, including insoluble organic material. This was evident by the significant fraction of submicrometer suspended insoluble particles present in the water extract and by the reduced insoluble material on the filters after the extraction process. More than half of the elemental carbon (EC) was on average missing from the filters after the water extraction. Significant EC concentrations were measured in the produced aerosol that was used as input to the AMS during the offline analysis

Water soluble reactive phosphate (SRP) in atmospheric particles over East Mediterranean: The importance of dust and biomass burning events

International audienceThe importance of dust and biomass burning episodes on the atmospheric concentration of water-soluble reactivephosphate (SRP) was determined in the eastern Mediterranean. SRP was measured with a new rapid real-time automatedanalytical system with a time resolution of a few minutes per sample and with an extremely low detectionlimit. The average atmospheric concentration of SRP during the sampling campaign was estimated at 0.35±0.25 (median0.30) nmol P m−3. The maximum concentration of SRP (3.08 nmol P m−3) was recorded during an intense dustepisode, and was almost ten times higher than the campaign average, confirming that Saharan dust was an importantprimary source of bioavailable P to the eastern Mediterranean, especially during the spring period when 60% of theevents occurred. Predicted increases in the frequency and intensity of dust storms in the area will enhance the roleof the atmosphere as a source of bioavailable P for the Mediterranean marine ecosystem. During the warm period,when Northerly winds prevailed, biomass burning processes contributed significantly to soluble phosphorus deliveredfrom atmospheric sources to the easternMediterranean. These inputs during warm periods are especially important forthe Eastern Mediterranean, where biological productivity is strongly limited by nutrient availability

Properties and Atmospheric Oxidation of Norpinic Acid Aerosol

Norpinic acid is a major semi-volatile oxidation product of α-pinene and β-pinene, two of the most important biogenic atmospheric volatile organic compounds. In this study we characterized the physicochemical properties of norpinic acid aerosol using a variety of techniques, and we investigated its reaction with OH radicals. The Aerosol Mass Spectrometer (AMS) spectrum of norpinic acid was characterized by a pronounced peak at m/z 82 (C5H6O+), which can be used as its chemical signature. The measured density of norpinic acid particles was 1.3 g cm−3. Its saturation concentration at 298 K was estimated to be equal to 8.9 μg m−3 using thermodenuder measurements and 12.8 μg m−3 using isothermal dilution. Its vaporization enthalpy was equal to 71 kJ mol−1. After reaction with OH radicals for an equivalent atmospheric period of 0.6–5 days under UV radiation and low RH, there were no noticeable changes in the AMS spectrum of the particles, while the wall-loss corrected mass concentration slightly decreased. This suggests that the atmospheric aging products of norpinic acid particles are quite similar to the parent molecule when measured by the AMS, and the aging reactions lead to a small change in particle mass concentration

Summertime particulate matter and its composition in Greece

During the summer of 2012 a coordinated field campaign was conducted in multiple locations in Greece in order to characterize the ambient particulate matter (PM) levels, its chemical composition and the contribution of the regional and local sources. PM1, PM2.5 and PM10 samples were collected simultaneously at seven different sites in Greece: an urban and a suburban station in Patras, a suburban station in Thessaloniki, a suburban and an urban background station in Athens, a rural background station at the Navarino Environmental Observatory (NEO) in southwestern Peloponnese and a remote background site at Finokalia in the northeastern part of Crete. The sites were selected to facilitate the estimation of the contribution of the local emission sources and long range transport. Sulfate and organics were the major PM1 components in all sites suggesting that high sulfate levels still remain in parts of Europe. The photochemistry of the Eastern Mediterranean can convert rapidly the emitted sulphur dioxide to sulfate. Our analysis indicated significant sulfate production over the area, with high sulfate levels, especially in the remote site of Finokalia, associated with air masses that had passed over Turkey. There was high regional secondary organic aerosol production dominating organic aerosol levels even in a major city like Athens. High organic aerosol levels were associated with air masses that had crossed the Balkans with a significant biogenic component. The average PM2.5 concentration ranged from 13 to 18 μg m−3 in the different sites. There were unexpected significant gradients in the concentrations of secondary aerosol components in length scales of a few hundred kilometers. The low concentrations of measured PM2.5 nitrate are mostly organic nitrates and supermicrometer nitrate associated with sea-salt and dust. Dust was a significant PM10 constituent in all areas and was quite variable in space showing the importance of the local sources