Angelo Cecinato

Emission of short chained organic acids, aldehydes and monoterpenes from Quercus ilex L. and Pinus pinea L. in relation to physiological activities, carbon budget and emission algorithms

We report on the emission of monoterpenes, short-chained organic acids and aldehydes from Mediterranean oak (Quercus ilex L.) and pine (Pinus pinea L.). All studies were done with dynamic cuvettes enclosing intact branches at the top of the canopy flushed with ambient air. Daily trends are compared with the photosynthetic active radiation (PAR), leaf temperature and the physiological activities of the enclosed branches, i.e. assimilation and transpiration, with special attention on the carbon budget. Oak emits monoterpenes in high amounts, up to 2% of the assimilated carbon. As compared with monoterpenes, short-chained organic acids and aldehydes are of minor importance for oak. However, on a leaf dry-weight basis equal amounts of acids and aldehydes are released from oak and pine. As pine emitted only low amounts of terpenes (below 0.2% of the assimilated carbon) the release of terpenes and oxygenated compounds is of equal importance for this species. A comparison of a modelled light and temperature driven emission with the observed volatile organic compounds (VOC) emissions showed good agreement for monoterpenes as well as for organic acids emitted in the case of oak. For pine only the release of acids showed an adequate relation to the algorithm data, whereas the terpene emissions seemed to be dominated by temperature effects.

Emission of monoterpenes and isoprene from a Mediterranean oak species Quercus ilex L. measured within the BEMA (Biogenic Emissions in the Mediterranean Area) project

Abstract We report on some results of our studies of monoterpene and isoprene emissions and the physiological activities of an oak species (Quercus ilex L.) under the Mediterranean climatic conditions found at Castel Porziano (Rome) in June 1993. The oak species Quercus ilex L. was found to emit mainly monoterpenes in high amounts. Isoprene emissions were negligible. Diel cycles of monoterpene emissions showed correlation with light and the diel behaviour of photosynthetic CO2 assimilation, transpiration and stomatal conductance. Temperature dependence seemed to be of minor importance.

Influence of Environmental Factors and Air Composition on the Emission of [alpha]-Pinene from Quercus ilex Leaves

We studied the emission of [alpha]-pinene from Quercus ilex leaves. Only the abaxial side of the hypostomatous Q. ilex leaf emits [alpha]-pinene. Light induced photosynthesis and [alpha]-pinene emission. However, the response of photosynthesis to dark-to-light transitions was faster than that of [alpha]-pinene, suggesting that ATP controls the emission. The emission was higher at 30 than at 20[deg]C, whereas photosynthesis did not change. Therefore, the relationship between photosynthesis and [alpha]-pinene emission does not always hold. When CO2 was removed from the air, transpiration was stimulated but photosynthesis and [alpha]-pinene emission were inhibited. [alpha]-Pinene inhibition was more rapid under low O2. When CO2 in the air was increased, photosynthesis was stimulated and transpiration was reduced, but [alpha]-pinene emission was unaffected. Therefore, the emission depends on the availability of photosynthetic carbon, is not saturated at ambient CO2, and is not dependent on stomatal opening. The pattern of [alpha]-pinene emission from Q. ilex is different from that of plants having specialized structures for storage and emission of terpenes. We suggest that [alpha]-pinene emitted by Q. ilex leaves is synthesized in the chloroplasts and shares the same biochemical pathway with isoprene emitted by isoprene-emitting oak species.

Evidence of the Photosynthetic Origin of Monoterpenes Emitted by Quercus ilex L. Leaves by 13C Labeling.

The carbon of the four main monoterpenes emitted by Quercus ilex L. leaves was completely labeled with 13C after a 20-min feeding with 99% 13CO2. This labeling time course is comparable with the labeling time course of isoprene, the terpenoid emitted by other Quercus species and synthesized in leaf chloroplasts. It is also comparable with that of phosphoglyceric acid. Our experiment therefore provides evidence that monoterpenes emitted by Q. ilex are formed from photosynthesis intermediates and may share the same synthetic pathway with isoprene. By analyzing the rate and the distribution of labeling in the different fragments, we looked for evidence of differential carbon labeling in the [alpha]-pinene emitted. However, the labeling pattern was quite uniform in the different fragments, suggesting that the carbon skeleton of the emitted monoterpenes comes from a unique carbon source.

Particulate n-alkanes, n-alkanoic acids and polycyclic aromatic hydrocarbons in the atmosphere of Algiers City Area

Abstract The concentrations of particulate organic matter were measured from May to September 1998 in urban area of Algiers and in municipal waste landfill of Oued Smar. For the sake of comparability, organic aerosols were also monitored at Montelibretti (Italy) in June of the same year. In addition to n-alkanes and polycyclic aromatic hydrocarbons (PAH), monocarboxylic n-alkanoic acids accounted for a large portion of identified organic compounds of aerosol at both Algerian sites. All these species were more abundant at Oued Smar than in downtown Algiers. At the urban site, concentration levels reached by n-alkanes and PAH highlighted the strong impact of motor vehicle emission resulting over the city area. Instead, at the Oued Smar landfill n-alkane and PAH contents depended upon the nature and account of the wastes burnt, and their behaviours were consistent with a pyrolytic origin. n-Alkanoic acids rather originated from the bacterial activity. By contrast, n-alkanes and n-alkanoic acids at Montelibretti seemed to be released by biogenic sources, whereas PAH presence was related to downwind transport of air parcels from Rome metropolitan area.

Formation and transport of 2‐nitrofluoranthene and 2‐nitropyrene of photochemical origin in the troposphere

The occurrence of 2-nitrofluoranthene and 2-nitropyrene in particulate matter collected in urban, suburban, forest, and remote areas located in Europe, America, Asia, and Antarctica was investigated. The results obtained confirm the photochemical origin of these components by gas phase reactions with OH radicals and their ubiquitous occurrence in the troposphere. An important role in their formation and dispersion seems to be played by carbon particles.

Nitro-PAH in ambient particulate matter in the atmosphere of Athens.

Nitrated polynuclear aromatic hydrocarbons (NPAH) with a molecular mass of 247 Daltons were found in soot collected in downtown Athens during a campaign performed in 1996. In particular, 2-nitrofluoranthene (2-NFa) and 2-nitropyrene (2-NPy), which are mainly related to photo-induced chemical processes occurring in the atmosphere, were more abundant than 1-nitropyrene (1-NPy) usually associated to motor vehicle exhaust.

Ubiquitous occurrence of semi-volatile carbonyl compounds in tropospheric samples and their possible sources

Abstract The levels of semi-volatile aldehydes with 4–10 carbon atoms and a ketone identified as 6-methyl-5-hepten-2-one by mass spectrometry have been measured in some urban, suburban and forest areas together with important hydrocarbons emitted by man-made (benzene, toluene) and biogenic sources (α-pinene). The results obtained show the ubiquitous occurrence of these carbonyl compounds in the atmospheric environment. Diurnal profiles obtained at various sites and a vertical gradient measured in a pine forest seem to be consistent with their natural origin. Direct emission from plants seems to be a major source for these components in the atmospheric boundary layer. The levels measured indicate that they are among the most abundant gaseous organic components present in natural environments.

Use of the isoprene algorithm for predicting the monoterpene emission from the Mediterranean holm oak Quercus ilex L.: Performance and limits of this approach

The algorithm developed by Guenther et al. [1991] to describe the organic emission of isoprene-emitting plants has been used for predicting monoterpene emission from Quercus ilex L., an evergreen oak typical of the Mediterranean basin. The dependence of monoterpene emission on photosynthetically active radiation and temperature has been verified through laboratory experiments carried out on single leaves as well as through field measurements at branch level. While the algorithm describes well monoterpene emission under stationary state conditions, it is less accurate when rapid fluctuations of light and temperature take place. Because of this, the isoprene algorithm is capable of predicting the response of Quercus ilex L. with an accuracy better than ±25% only in 65% of the environmental situations experienced by the plant. Field and laboratory observations consistently indicate that temperature oscillations can be an important source for the discrepancies between predicted and observed values as they can generate bursts of emission with values twice as high as those predicted by the algorithm. Possible causes generating these effects are analyzed and critically discussed. In spite of the observed limitations, the isoprene algorithm can successfully describe the biogenic emission from Quercus ilex L., and its use is advantageous as it greatly simplifies regional and global emission models, especially if the light dependence of monoterpene emission is proven to be a widespread phenomenon.

Distribution of n-alkanes, polynuclear aromatic hydrocarbons and nitrated polynuclear aromatic hydrocarbons between the fine and coarse fractions of inhalable atmospheric particulates

The distribution ratios of n-alkanes, polynuclear aromatic hydrocarbons (PAHs) and nitrated PAH components between fine and coarse fractions of soot has been investigated in downtown Rome through three field campaigns carried out at different times of the year. The preferential accumulation of almost all species investigated onto fine particles has been observed in all field experiments performed. Moreover, nitrated PAHs had varied distributions, according to the origin of their occurrence in the atmosphere; in fact, congeners of photochemical origin accumulated more in fine particles than those released by primary sources.