Elemental composition of atmospheric particulate matter during 2006 wet season at a rural background site in Tanzania

The elemental composition of PM10 was studied during 2006 wet season in a rural background site of Morogoro, Tanzania. A Gent PM10 stacked filter unit sampler with coarse and fine Nuclepore polycarbonate filters, providing fine (0.4 μm) and coarse (8 μm) size fractions, was deployed. A total of 29 collections were analysed for the PM mass by weighing. A further analysis was performed for 25 elements by particle-induced x-ray emission spectrometry. The results show  that the concentrations of the heavy metals were lower than those for the elements of crustal origin. The data from PIXE analysis and enrichment factor  (E.F.) calculation, using Fe as a reference of crustal material, showed that for the coarse size fraction, most elements have crustal EFs that are very close to one, while enriched elements (E.F. > 10) like S, Cl, Zn, As, Br, Pb and BC, predominated in fine (PM2) size fraction (an anthropogenic origin can be suggested for the later). Potassium a well-known indicator for biomass burning was mostly associated with the fine particles (as around 56% of the PM10 K was in the PM2 size fraction). This suggests that biomass burning was important in Morogoro. Five-day isentropic backward trajectories as determined by the air trajectory HYSPLIT model were computed for Morogoro and the allocated sector of oceanic origin over continental, mainly through Mozambique and Tanzania) was the most common. However, other sectors such as Oceanic, over Madagascar or continental origins were observed. @JASEMJ. Appl. Sci. Environ. Manage. December, 2010, Vol. 14 (4) 135 – 13

Chirality and the origin of atmospheric humic-like substances

Aerosol water extracts and atmospheric humic-like substances (HULIS) obtained from PM2.5-fraction aerosol samples collected in a rural/continental background environment and in an urban environment in spring and summer, and at a tropical site that was heavily impacted by biomass burning were studied. HULIS was obtained as the water-soluble, methanol-elutable material isolated from a solid-phase extraction procedure. The mean organic matter-to-organic carbon mass conversion factor and the standard deviation of 2.04 +/- 0.06 were derived for HULIS from biomass burning. Mean atmospheric concentrations of HULIS for the rural and urban environments and for the biomass burning during daylight periods and nights, were 1.65, 2.2, 43, and 60 mu gm(-3), respectively. This and other abundances indicate that intense emission sources and/or formation mechanisms of HULIS operate in biomass burning. Mean contributions of C in HULIS (HULIS-C) to water-soluble organic carbon (WSOC) were 35, 48, 63, and 76%, respectively, for the sample set listed. HULIS-C is the major component of the WSOC in tropical biomass burning. The data also suggest that HULIS most likely do not share common origin in the three environments studied. Differentiation among the possible formation processes was attempted by investigating the optical activity of HULIS through their (electronic and vibrational) circular dichroism properties. The urban HULIS did not show optical activity, which is in line with the concept of their major airborne formation from anthropogenic aromatics. The rural HULIS revealed weak optical activity, which may be associated with one of their important formation pathways by photo-oxidation and oligomerisation, i.e., with the formation from chiral biogenic precursors with one of the enantiomers slightly enriched. The The biomass burning of HULIS exhibited a strong effect in the vibrational circular dichroism as a clear distinction from the other two types. This was related to the contribution of the thermal degradation products of lignins and cellulose. The biomass burning of HULIS resemble Suwannee River Fulvic Acid standard more closely in some aspects than the urban and rural types of HULIS, which may be related to their common origin from plant material

Semivolatile behaviour and filter sampling artifacts for dicarboxylic acids during summer campaigns at three forested sites in Europe

The sampling artifacts for C(2)-C(5) dicarboxylic acids (DCAs) were studied by collecting high-volume PM(2.5) samples using front and back quartz-fibre filters. The filters were analysed for carbonaceous components, and for inorganic cationic and anionic and organic anionic species. Back/front filter ratios were determined for the C(2)-C(5) DCAs, but also for methanesulphonate (MSA(-)), the various inorganic species, and the carbonaceous components. The sampling artifacts for the inorganic species were small (< 5%) with the exception of those for nitrate. The median back/front filter ratios for MSA(-) and the C(2)-C(5)DCAs increased in the following order: oxalate (1.5%)-succinate (3%)-MSA(-) (4%)-malonate (2%-9%)-glutarate (7%-26%). Most of these ratios are smaller than those that were obtained for organic carbon, total carbon, and especially water-soluble organic carbon. Our back/front ratios for the C(2)-C(5) DCAs are lower to much lower than those found in other studies

Molecular characterization of polar organosulfates in secondary organic aerosol from the green leaf volatile 3-Z-hexenal

Evidence is provided That the green leaf volatiles 3-Z- hexenal serves as a precursor for biogenic secondary organic aersol through the formation of polar organosulfates (Os) with molecular weight (MW) 226. The MW 226 C-6-OSs were Chemically elucidated, along with structurally similar MW 212 C-5-OSs, whose biogenic precursor is likely related to 3-Z-hexenal but still remains unknown. The MW: 226 and 212 OSs have a substantial abundance in ambient fine aerosol from K-puszta, Hungary, which is comparable to that of the isoprene-related MW 216 OSs, known to be formed: through sulfation of C-5-epoxydiols, second-generation gas-phase photooxidation products of isoprene. Using detailed interpretation of negative-ion electrospray ionization mass spectral data, the MW 226, compounds are assigned to isomeric sulfate esters of 3,4-dihydroxyhex-5-enoic acid with the sulfate group located or C-4 position. Two MW 212 compounds present in: ambient fine aerosol are attributed to isomeric sulfate :esters of 2,3-dihydroxypent-4-enoic acid, of which two are sulfated at C-3 and one is sulfated at C-2. The formation of the MW 226 :OSs is tentatively explained through photooxidation of 3-Z-hexenal in, the gas phase, resulting in alkoxy radical, followed by a rearrangement and subsequent sulfation of the epoxy group in the particle phase

Monitoring of atmospheric aerosol particles on the Antarctic Peninsula

Atmospheric aerosol particles have been sampled since 1985 at the Brazilian Antarctic station, Comandante Ferraz (62 degrees 05' S, 58 degrees 23.5' W). Stacked filter units were used to collect particles with an aerodynamic diameter of less than 10 mu m. The elemental concentration Was measured by particle-induced X-ray emission, yielding data for 23 elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Rb, Sr, Zr and Pb. The detection limit was typically near 5 ng m(-3) for elements with atomic number (Z) less than 20, and 0.1 ng m(-3) for 21 < Z < 30. Principal-factor and cluster analyses identified four sources for the Antarctic aerosol: fine and coarse sea salt, soil dust and sulphates. The fine-mode non-sea-salt sulphate concentration showed a clear seasonal pattern accompanying the biological cycle of algae, with minimum during winter. Some elements. such as Ni and Pb, showed very high enriched concentrations relative to the bulk sea-water composition. This indicates the existence of sources of regional or long-range transported pollution

High-molecular-weight esters in α-pinene ozonolysis secondary organic aerosol : structural characterization and mechanistic proposal for their formation from highly oxygenated molecules

Stable high-molecular-weight esters are present in alpha-pinene ozonolysis secondary organic aerosol (SOA) with the two most abundant ones corresponding to a hydroxypinonyl ester of cis-pinic acid with a molecular weight (MW) of 368 (C19H28O7) and a diaterpenylic ester of cis-pinic acid with a MW of 358 (C17H26O8). However, their molecular structures are not completely elucidated and their relationship with highly oxygenated molecules (HOMs) in the gas phase is still unclear. In this study, liquid chromatography in combination with positive ion electrospray ionization mass spectrometry has been performed on highmolecular- weight esters present in alpha-pinene ozonolysis SOA with and without derivatization into methyl esters. Unambiguous evidence could be obtained for the molecular structure of the MW368 ester in that it corresponds to an ester of cis-pinic acid where the carboxyl substituent of the dimethylcyclobutane ring and not the methylcarboxyl substituent is esterified with 7-hydroxypinonic acid. The same linkage was already proposed in previous work for the MW358 ester (Yasmeen et al., 2010), but could be supported in the present study. Guided by the molecular structures of these stable esters, we propose a formation mechanism from gas-phase HOMs that takes into account the formation of an unstable C19H28O11 product, which is detected as a major species in alpha-pinene ozonolysis experiments as well as in the pristine forest atmosphere by chemical ionization-atmospheric pressure ionization-time-of-flight mass spectrometry with nitrate clustering (Ehn et al., 2012, 2014). It is suggested that an acyl peroxy radical related to cis-pinic acid (RO2 center dot) and an alkoxy radical related to 7-or 5-hydroxypinonic acid (R'O center dot) serve as key gas-phase radicals and combine according to a RO2 + R'O center dot -> RO3R' radical termination reaction. Subsequently, the unstable C19H28O11 HOM species decompose through the loss of oxygen or ketene from the inner part containing a labile trioxide function and the conversion of the unstable acyl hydroperoxide groups to carboxyl groups, resulting in stable esters with a molecular composition of C19H28O7 (MW368) and C17H26O8 (MW358), respectively. The proposed mechanism is supported by several observations reported in the literature. On the basis of the indirect evidence presented in this study, we hypothesize that RO2 + R'O center dot -> RO3R' chemistry is at the underlying molecular basis of high-molecular-weight ester formation upon alpha-pinene ozonolysis and may thus be of importance for new particle formation and growth in pristine forested environments

Characterization of oligomers from methylglyoxal under dark conditions : a pathway to produce secondary organic aerosol through cloud processing during nighttime

Aqueous-phase oligomer formation from methylglyoxal, a major atmospheric photooxidation product, has been investigated in a simulated cloud matrix under dark conditions. The aim of this study was to explore an additional pathway producing secondary organic aerosol (SOA) through cloud processes without participation of photochemistry during nighttime. Indeed, atmospheric models still underestimate SOA formation, as field measurements have revealed more SOA than predicted. Soluble oligomers (n = 1-8) formed in the course of acid-catalyzed aldol condensation and acid-catalyzed hydration followed by acetal formation have been detected and characterized by positive and negative ion electrospray ionization mass spectrometry. Aldol condensation proved to be a favorable mechanism under simulated cloud conditions, while hydration/acetal formation was found to strongly depend on the pH of the system and only occurred at a pH < 3.5. No evidence was found for formation of organosulfates. The aldol oligomer series starts with a beta-hydroxy ketone via aldol condensation, where oligomers are formed by multiple additions of C3H4O2 units (72 Da) to the parent beta-hydroxy ketone. Ion trap mass spectrometry experiments were performed to structurally characterize the major oligomer species. A mechanistic pathway for the growth of oligomers under cloud conditions and in the absence of UV-light and OH radicals, which could substantially enhance in-cloud SOA yields, is proposed here for the first time

Chemical composition and mass closure for fine and coarse aerosols at a kerbside in Budapest, Hungary, in spring

ABSTRACT A comprehensive chemical aerosol characterisation was carried out at a kerbside in downtown Budapest in spring 2002. Several filter samplers were deployed in parallel for day and night collections, and a total of 23 parallel collections were made. All samples were analysed for the particulate mass (PM) by weighing. Depending upon the sampler type and/or collection substrate, further analyses were done for up to 46 elements by a combination of PIXE and instrumental neutron activation analysis (INAA), for major anions and cations by ion chromatography, and for organic carbon and elemental carbon by a thermal-optical transmission technique. Aerosol chemical mass closure calculations were done for the separate fine (&lt;2 µm) and coarse (2-10 µm) size fractions. For reconstituting the gravimetric PM, eight aerosol types were considered, whereby three aerosol types were deduced from the PIXE/INAA elemental data set. Organic matter (OM) and elemental carbon were the dominant aerosol types in the fine fraction; they explained on average 43 and 21% of the fine PM. The coarse PM consisted mainly of crustal matter (49%) and of OM (30%). The large contribution from crustal matter (road dust) to the coarse fraction is consistent with other data from kerbside sites in Europe