Légköri szerves aeroszol másodlagos keletkezési mechanizmusának tanulmányozása = Study on secondary organic aerosol formation

Munkánk során bemutattuk, hogy a másodlagos aeroszol keletkezési mechanizmusában a multifázisú folyamatok nagy jelentőséggel bírnak. Aromás modellvegyületekből hidroxilgyökkel történő reakció során, gyökös mechanizmussal, a kiindulási anyagoknál nagyobb molekulatömegű alkotók keletkeznek. Feltételezhető, hogy az oligomerizációs reakcióban néhány aromás gyűrű illetve a reakció során keletkező termék kapcsolódik össze. Kutatásaink eredményei alapján valószínűsíthető, hogy hasonló átalakulási folyamatok játszódhatnak le légköri aeroszolban is, melyek a légköri aeroszol kémiai tulajdonságait is befolyásolják. A légköri aeroszol humuszszerű anyagainak csoportjába tartozó szerves szulfát vegyületek keletkezési mechanizmusát tekintve feltételezhető, hogy azok a fotokémiai reakciók során keletkező anyagok kémiai reakcióval történő átalakulása után már meglevő aeroszol részecskék felületén képződnek. Ködkamra kísérletek során gyűjtött minták elemzésével kapott eredmények alapján feltételezhető, hogy humuszszerű anyagok másodlagos folyamatokban a növények által emittált illékony szerves anyagokból is keletkezhetnek. | It has been shown that multiphase processes represent an important yet previously overlooked formation mechanism of secondary organic aerosol. In the reaction of OH radicals with aromatic model compounds in the aqueous phase higher molecular weight compounds were found to form by radical reaction mechanisms. It was assumed that during the oligomerisation reactions a few aromatic ring and/or the reaction products form condensed structures. Based on our studies it can be hypothesized that similar reaction mechanisms might take place in atmospheric aerosols altering their chemical properties. It was shown that organosulphates, which are recently discovered and important SOA components and possibly part of atmospheric HULIS may form in surface reactions on pre-existing aerosols in chemical reactions with compounds formed in photochemical processes. Our results obtained from the analysis of samples collected from smog chamber experiments showed that humic-like substances might also be generated in secondary processes from volatile organic compounds emitted by the vegetation

Brown carbon absorption in the red and near-infrared spectral region

Black carbon (BC) aerosols have often been assumed to be the only light-absorbing carbonaceous particles in the red and near-infrared spectral regions of solar radiation in the atmosphere. Here we report that tar balls (a specific type of organic aerosol particles from biomass burning) do absorb red and near-infrared radiation significantly. Tar balls were produced in a laboratory experiment, and their chemical and optical properties were measured. The absorption of these particles in the range between 470 and 950 nm was measured with an aethalometer, which is widely used to measure atmospheric aerosol absorption.We find that the absorption coefficient of tar balls at 880 nm is more than 10% of that at 470 nm. The considerable absorption of red and infrared light by tar balls also follows from their relatively low absorption Ångström coefficient (and significant mass absorption coefficient) in the spectral range between 470 and 950 nm. Our results support the previous finding that tar balls may play an important role in global warming. Due to the non-negligible absorption of tar balls in the near-infrared region, the absorption measured in the field at near-infrared wavelengths cannot solely be due to soot particles

Light absorption properties of laboratory-generated tar ball particles

Tar balls (TBs) are a specific particle type that is abundant in the global troposphere, in particular in biomass smoke plumes. These particles belong to the family of atmospheric brown carbon (BrC), which can absorb light in the visible range of the solar spectrum. Albeit TBs are typically present as individual particles in biomass smoke plumes, their absorption properties have been only indirectly inferred from field observations or calculations based on their electron energy-loss spectra. This is because in biomass smoke TBs coexist with various other particle types (e.g., organic particles with inorganic inclusions and soot, the latter emitted mainly during flaming conditions) from which they cannot be physically separated; thus, a direct experimental determination of their absorption properties is not feasible. Very recently we have demonstrated that TBs can be generated in the laboratory from droplets of wood tar that resemble atmospheric TBs in all of their observed properties. As a follow-up study, we have installed on-line instruments to our laboratory set-up, which generate pure TB particles to measure the absorption and scattering, as well as the size distribution of the particles. In addition, samples were collected for transmission electron microscopy (TEM) and total carbon (TC) analysis. The effects of experimental parameters were also studied. The mass absorption coefficients of the laboratory-generated TBs were found to be in the range of 0.8–3.0m2

Atmospheric tar balls: aged primary droplets from biomass burning?

Atmospheric tar balls are particles of special morphology and composition that are fairly abundant in the plumes of biomass smoke. These particles form a specific subset of brown carbon (BrC) which has been shown to play a significant role in atmospheric shortwave absorption and, by extension, climate forcing. Here we suggest that tar balls are produced by the direct emission of liquid tar droplets followed by heat transformation upon biomass burning. For the first time in atmospheric chemistry we generated tar-ball particles from liquid tar obtained previously by dry distillation of wood in an all-glass apparatus in the laboratory with the total exclusion of flame processes. The particles were perfectly spherical with a mean optical diameter of 300 nm, refractory, externally mixed, and homogeneous in the contrast of the transmission electron microscopy (TEM) images. They lacked any graphene-like microstructure and exhibited a mean carbon-to-oxygen ratio of 10. All of the observed characteristics of laboratory-generated particles were very similar to those reported for atmospheric tar-ball particles in the literature, strongly supporting our hypothesis regarding the formation mechanism of atmospheric tar-ball particles

Emission factors for PM10 and PAHs from illegal burning of different types of municipal waste in households

It is a common practice in the developing countries and in some regions of Europe that solid wastes generated in the households (e.g. plastic beverage packaging and other plastic wastes, textile wastes, fibreboards, furniture, tyres, and coloured paper waste) are burned in wood- or coal-fired stoves during the winter months. In Europe, the types and volume of municipal waste burned in households is virtually unknown because these activities are illegal and not recorded, with the exception of a few media reports or court cases. Even though particulate emissions from illegal waste burning pose an unprecedented hazard to human health due to the combination of excessive emission factors (EFs) and uncontrolled chemical composition, there is scarce information on the specific emission factors for PM10 and polycyclic aromatic hydrocarbons (PAHs) in the scientific literature. In this work, controlled combustion tests were performed with 12 different types of municipal solid waste and particulate emissions were measured and collected for chemical analysis. Absolute emission factors for PM10 and PAHs as well as the benzo(a)pyrene toxicity equivalent of the latter are reported for the first time for the indoor combustion of 12 common types of municipal solid waste that are frequently burned in households worldwide

Sampling and characterization of resuspended and respirable road dust

AbstractUrban air quality is severely affected by traffic related particulate matter, including direct emissions from exhaust, brake pad, tire wear and road dust resuspended by vehicular motions. Deposited road dust can also be resuspended by wind force or other anthropogenic activities, and overall it may contribute up to 30% to urban PM10. A mobile resuspended road dust PM10 sampler was developed and constructed which simulates the effects of traffic or gusting winds on road surfaces and collects resuspended PM1−10 samples in a cyclone separator and PM1 samples on filters. The sampler was tested by collecting resuspended road dust at kerbside locations in Veszprém, Hungary. The collected PM1 and PM1−10 fractions were analysed by various analytical methods to show the potential of size-selective on-line sample collection combined with the chemical characterization of resuspended road dust. The main constituents of the resuspended road dust were crustal elements, and it was also possible to determine the mineral phase composition of PM1−10 dust which is generally not feasible from samples collected on filter substrate. The application of the sampling and analysis methods may facilitate the evaluation of resuspended road dust sources in cities as well as help constrain a better source apportionment of urban PM10