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For the first time, ambient levels of benzene, toluene, carbon tetrachloride and selected oxygenated organic compounds have been measured in both populated and remote sites in the Sahara desert. The levels of these species were generally found to be high in the industrialized regions of the North Sahara, progressively decreasing with latitude so that lowest levels were reached in remote desert sites close to the Equator. The emissions from traffic, and the oil production and its transformation, together with the solvent use were the main anthropogenic sources determining the levels of aromatic, aliphatic and chlorinated organic compounds in desert sites near two Algerian cities. Substantial levels of acetone and some semi-volatile compounds, emitted or formed by photochemical reactions, were also found. Although some of these compounds were below the detection limits in the most remote sites of the Sahara desert located in Mauritania and Niger, measurable levels of benzene and toluene were still found together with significant amounts of acetone. Data seem to indicate that forest fires occurring in the tropical regions of the North African continent were the most likely sources for the background levels measured during most of our measurements. The data presented here did not differ too much from those measured in the most isolated sites of the northern hemisphere.

E' stato messo in evidenza come la composizione di composti organici volatili emessi dal Pioppo (Populus americana) sia un elemento fondamentale nell'attrarre l'insetto patogeno Chrysomela pupuli che ne determina la defioliazione e che il potere attrattivo è più elevato nelle piante giovani che emettono monoterpeni.

Flussi di isoprene e monoterpeni sono stati determinati in un sito della foresta Amazzonica mediante tre differenti metodi micro-meteorologici. Le misure degli isoprenoidi e dei loro prodotti di ossidazione ha permesso di stabilire che, in contrato con quello che si pensava comunemente, alte concentrazioni di radicali OH sono presenti nell'Atmospheric Boundary Layer di questi siti remoti. E' stato inoltre confermato che l'emissione di isoprenoidi rappresenta una frazione molto piccola della frazione di CO2 assimilata.

Una colonna capillare trattata con ciclodestrine è stata usata per l'analisi di BTX (tutti gli areni da benzne a dimetyilbenznei) in aria consentendo la separazione completa di tutti i componenti. Essa è stata usata per valutare le trasformazioni in atmosfera di questi composti in funzione della reattività delle masse d'aria a Roma e Montelibretti.

A method for the accurate detrmination of Volatile organic compouns (VOC) in milk samples has been developed and tested. It combines multiple dynamic haedspace extraction with GC-MS. The method has been used to follow the seasonal variations of monoterpenes and arenes in goat milk and to detect the impact of air pollution on the quality of milk

Texto completo: acesso restrito. p. 663–682 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-12-13T11:31:57Z No. of bitstreams: 1 T. M. TAVARES.pdf: 508567 bytes, checksum: 3bcafc9b74a420ec502226c475b5a03b (MD5) Made available in DSpace on 2013-12-13T11:31:57Z (GMT). No. of bitstreams: 1 T. M. TAVARES.pdf: 508567 bytes, checksum: 3bcafc9b74a420ec502226c475b5a03b (MD5) Previous issue date: 2004 Whereas for extra-tropical regions model estimates of the emission of volatile organic compounds (VOC) predict strong responses to the strong annual cycles of foliar biomass, light intensity and temperature, the tropical regions stand out as a dominant source year round, with only little variability mainly due to the annual cycle of foliar biomass of drought-deciduous trees. As part of the Large Scale Biosphere Atmosphere Experiment in Amazônia (LBA-EUSTACH), a remote secondary tropical forest site was visited in the dry-to-wet season transition campaign, and the trace gas exchange of a strong isoprene emitter and a monoterpene emitter are compared to the wet-to-dry season transition investigations reported earlier. Strong seasonal differences of the emission capacity were observed. The standard emission factor for isoprene emission of young mature leaves of Hymenaea courbaril was about twofold in the end of the dry season (111.5 μgC g−1 h−1 or 41.2 nmol m−2 s−1) compared to old mature leaves investigated in the end of the wet season (45.4 μgC g−1 h−1 or 24.9 nmol m−2 s−1). Standardized monoterpene emission rate of Apeiba tibourbou were 2.1 and 3.6 μgC g−1 h−1 (or 0.3 and 0.8 nmol m−2 s-1), respectively. This change in species-specific VOC emission capacity was mirrored by a concurrent change in the ambient mixing ratios. The growth conditions vary less in tropical areas than in temperate regions of the world, and the seasonal differences in emission strength could not be reconciled solely with meteorological data of instantaneous light intensity and temperature. Hence the inadequacy of using a single standard emission factor to represent an entire seasonal cycle is apparent. Among a host of other potential factors, including the leaf developmental stage, water and nutrient status, and abiotic stresses like the oxidative capacity of the ambient air, predominantly the long-term growth temperature may be applied to predict the seasonal variability of the isoprene emission capacity. The dry season isoprene emission rates of H. courbaril measured at the canopy top were also compared to isoprene emissions of the shade-adapted species Sorocea guilleminiana growing in the understory. Despite the difference in VOC emission composition and canopy position, one common algorithm was able to predict the diel emission pattern of all three tree species.

Texto completo: acesso restrito. p. 663–682 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-12-13T11:31:57Z No. of bitstreams: 1 T. M. TAVARES.pdf: 508567 bytes, checksum: 3bcafc9b74a420ec502226c475b5a03b (MD5) Made available in DSpace on 2013-12-13T11:31:57Z (GMT). No. of bitstreams: 1 T. M. TAVARES.pdf: 508567 bytes, checksum: 3bcafc9b74a420ec502226c475b5a03b (MD5) Previous issue date: 2004 Whereas for extra-tropical regions model estimates of the emission of volatile organic compounds (VOC) predict strong responses to the strong annual cycles of foliar biomass, light intensity and temperature, the tropical regions stand out as a dominant source year round, with only little variability mainly due to the annual cycle of foliar biomass of drought-deciduous trees. As part of the Large Scale Biosphere Atmosphere Experiment in Amazônia (LBA-EUSTACH), a remote secondary tropical forest site was visited in the dry-to-wet season transition campaign, and the trace gas exchange of a strong isoprene emitter and a monoterpene emitter are compared to the wet-to-dry season transition investigations reported earlier. Strong seasonal differences of the emission capacity were observed. The standard emission factor for isoprene emission of young mature leaves of Hymenaea courbaril was about twofold in the end of the dry season (111.5 μgC g−1 h−1 or 41.2 nmol m−2 s−1) compared to old mature leaves investigated in the end of the wet season (45.4 μgC g−1 h−1 or 24.9 nmol m−2 s−1). Standardized monoterpene emission rate of Apeiba tibourbou were 2.1 and 3.6 μgC g−1 h−1 (or 0.3 and 0.8 nmol m−2 s-1), respectively. This change in species-specific VOC emission capacity was mirrored by a concurrent change in the ambient mixing ratios. The growth conditions vary less in tropical areas than in temperate regions of the world, and the seasonal differences in emission strength could not be reconciled solely with meteorological data of instantaneous light intensity and temperature. Hence the inadequacy of using a single standard emission factor to represent an entire seasonal cycle is apparent. Among a host of other potential factors, including the leaf developmental stage, water and nutrient status, and abiotic stresses like the oxidative capacity of the ambient air, predominantly the long-term growth temperature may be applied to predict the seasonal variability of the isoprene emission capacity. The dry season isoprene emission rates of H. courbaril measured at the canopy top were also compared to isoprene emissions of the shade-adapted species Sorocea guilleminiana growing in the understory. Despite the difference in VOC emission composition and canopy position, one common algorithm was able to predict the diel emission pattern of all three tree species.

For the first time, the emission of individual BVOC released from a Mediterranean ecosystem has been assessed and the results obtained have been directly compared with fluxes measured with the mixed box (MB) approach. The study was conducted in Pianosa, a very small and flat island located in the Tyrrhenian sea, between the coasts of Central Italy and the Corsica Island. Due to the substantial lack of man-made emission and the restricted access, terrestrial vegetation represents in this island the main source of hydrocarbons. This allows to use simple methodologies to estimate and measure the emission of individual BVOC in the atmosphere. Due to the limited number of emitting species, the total emission was estimated by up-scaling to ecosystem level the information obtained with branch enclosures. Data obtained suggested that the basal emission of total isoprenoids generated from the island was one order of magnitude smaller than that estimated in the pine-oak forest ecosystem of Castelporziano (ca. 0.2 mg C m-2h-1). ±-Pinene was the major component emitted and accounted, by itself, for more than 40% of the total isoprenoid emission. Daily profiles of emission were calculated for the two days when the air masses were depleted in anthropogenic compounds, after traveling for two days over the open sea. Results obtained in these days indicated that ±-pinene was the only component displaying an emission (ca. 0.1 mg C m-2 h-1) sufficiently high to generate detectable concentrations (0.01-0.03 ¼g C Nm-3) in the atmospheric boundary layer (ABL). Fluxes determined using the MB approach substantially confirmed the estimates made by up-scaling to ecosystem level the emission from terrestrial vegetation, although a difference of a factor of two was observed between the calculated emission and the measured fluxes. Reasons explaining these differences will be analyzed and critically discussed.

Concentrations of isoprenoids and anthropogenic VOC in different seasons have been measured in the tropical site of Rondonia. A strong seasonality of isoprene, carbonyls and acids has been observed.

Texto completo: acesso restrito. p. 1-13 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-01-20T13:09:29Z No. of bitstreams: 1 T. M. Tavares.pdf: 812861 bytes, checksum: d8d63d112e4410e0f70a281011990014 (MD5) Made available in DSpace on 2014-01-20T13:09:29Z (GMT). No. of bitstreams: 1 T. M. Tavares.pdf: 812861 bytes, checksum: d8d63d112e4410e0f70a281011990014 (MD5) Previous issue date: 2002 As part of the project LBA-EUSTACH (European Studies on Trace gases and Atmosphere Chemistry as a contribution to the Large-Scale Biosphere-Atmosphere experiment in Amazonia), we examined the diel pattern of isoprenoid exchange in the wet season of 1999 at a remote field site in Rondônia, Brazil. The emission pattern of two tree species in a secondary forest was investigated by means of a dynamic branch enclosure system and was compared on the basis of climatological variables like temperature and light and physiological parameters such as assimilation, transpiration, and stomatal conductance. While the species Hymenaea courbaril was found to be a strong isoprene emitter, Apeiba tibourbou was found to exclusively emit monoterpenes and no isoprene. Species-related standard emission factors calculated on a carbon basis were 45.4 μg g−1 h−1 (24.9 nmol m−2 s−1) for isoprene and 3.6 μg g−1 h−1 (0.75 nmol m−2 s−1) for monoterpene emission, representing a nontrivial carbon loss by the plants of 1.8% and 0.1% C relative to the net carbon assimilation on a daily basis. About 90% of the total monoterpene emission from A. tibourbou was comprised of sabinene, α-pinene, β-pinene, myrcene, and limonene, in decreasing quantity. Despite the difference in isoprenoid emission composition, the diel emission pattern of both tree species reacted similarly toward the environmental conditions, fluctuating light and temperature, indicating that closely related metabolic controls were involved in the actual emission. Both isoprene emission and monoterpene emission exhibited a light saturation curve similar to CO2 assimilation. No isoprenoid emission was found during nighttime. The strong light dependence of the monoterpene emission by A. tibourbou suggests that this tree species does not store monoterpenes but emits them immediately upon production. The diel pattern of both the isoprene and the monoterpene emission could be adequately simulated by current isoprene algorithms. The ambient air mixing ratios of isoprenoids were clearly dominated by isoprene, with peak values of 8 ppb inside the main canopy. Vertical gradients of ambient air mixing ratios in and above a primary rain forest site illustrated the emission of isoprene by the main canopy dependent upon light and temperature but were also indicative of a potential sink at the forest floor. For monoterpenes, corresponding gradients could hardly be resolved, reflecting observed ambient air mixing ratios more than an order of magnitude lower than for isoprene. Nevertheless, a strong diel cycle of short-lived monoterpene compounds like α-pinene was found in the primary as well as in the secondary forest site, which further strengthens our finding of a strong light dependence of biogenic monoterpene emission even on a larger scale. Our findings to some extent question the applicability of the commonly used monoterpene emission algorithm to the tropics. A strong light dependence of biogenic monoterpene emissions may, if generalized for tropical tree species in common, have a strong impact on estimated global flux rates for tropical regions.

Texto completo: acesso restrito. p. 1-13 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-01-20T13:09:29Z No. of bitstreams: 1 T. M. Tavares.pdf: 812861 bytes, checksum: d8d63d112e4410e0f70a281011990014 (MD5) Made available in DSpace on 2014-01-20T13:09:29Z (GMT). No. of bitstreams: 1 T. M. Tavares.pdf: 812861 bytes, checksum: d8d63d112e4410e0f70a281011990014 (MD5) Previous issue date: 2002 As part of the project LBA-EUSTACH (European Studies on Trace gases and Atmosphere Chemistry as a contribution to the Large-Scale Biosphere-Atmosphere experiment in Amazonia), we examined the diel pattern of isoprenoid exchange in the wet season of 1999 at a remote field site in Rondônia, Brazil. The emission pattern of two tree species in a secondary forest was investigated by means of a dynamic branch enclosure system and was compared on the basis of climatological variables like temperature and light and physiological parameters such as assimilation, transpiration, and stomatal conductance. While the species Hymenaea courbaril was found to be a strong isoprene emitter, Apeiba tibourbou was found to exclusively emit monoterpenes and no isoprene. Species-related standard emission factors calculated on a carbon basis were 45.4 μg g−1 h−1 (24.9 nmol m−2 s−1) for isoprene and 3.6 μg g−1 h−1 (0.75 nmol m−2 s−1) for monoterpene emission, representing a nontrivial carbon loss by the plants of 1.8% and 0.1% C relative to the net carbon assimilation on a daily basis. About 90% of the total monoterpene emission from A. tibourbou was comprised of sabinene, α-pinene, β-pinene, myrcene, and limonene, in decreasing quantity. Despite the difference in isoprenoid emission composition, the diel emission pattern of both tree species reacted similarly toward the environmental conditions, fluctuating light and temperature, indicating that closely related metabolic controls were involved in the actual emission. Both isoprene emission and monoterpene emission exhibited a light saturation curve similar to CO2 assimilation. No isoprenoid emission was found during nighttime. The strong light dependence of the monoterpene emission by A. tibourbou suggests that this tree species does not store monoterpenes but emits them immediately upon production. The diel pattern of both the isoprene and the monoterpene emission could be adequately simulated by current isoprene algorithms. The ambient air mixing ratios of isoprenoids were clearly dominated by isoprene, with peak values of 8 ppb inside the main canopy. Vertical gradients of ambient air mixing ratios in and above a primary rain forest site illustrated the emission of isoprene by the main canopy dependent upon light and temperature but were also indicative of a potential sink at the forest floor. For monoterpenes, corresponding gradients could hardly be resolved, reflecting observed ambient air mixing ratios more than an order of magnitude lower than for isoprene. Nevertheless, a strong diel cycle of short-lived monoterpene compounds like α-pinene was found in the primary as well as in the secondary forest site, which further strengthens our finding of a strong light dependence of biogenic monoterpene emission even on a larger scale. Our findings to some extent question the applicability of the commonly used monoterpene emission algorithm to the tropics. A strong light dependence of biogenic monoterpene emissions may, if generalized for tropical tree species in common, have a strong impact on estimated global flux rates for tropical regions.

Texto completo: acesso restrito. p. 1-13 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-01-20T13:26:23Z No. of bitstreams: 1 S. T. Oliva.pdf: 814795 bytes, checksum: d4f6f77bb2a5411243189df225dc06a2 (MD5) Made available in DSpace on 2014-01-20T13:26:23Z (GMT). No. of bitstreams: 1 S. T. Oliva.pdf: 814795 bytes, checksum: d4f6f77bb2a5411243189df225dc06a2 (MD5) Previous issue date: 2002 We measured atmospheric gas-phase volatile organic compounds (VOCs) at the end of the wet and end of the dry season at a tropical rainforest site in Rondônia, Brazil, using various sampling techniques such as trapping on different adsorbents or cryogenic trapping combined with appropriate analysis techniques. The measuring sites were located inside the forest of a biological reserve near Ji-Paraná. Sampling was performed from 3 May 1999 to 17 May 1999 and from 24 September 1999 to 2 November 1999 during the “wet-to-dry season transition” and “dry-to-wet season transition” periods in Rondônia, respectively. Samples were obtained at the canopy top close to the potential sources/sinks for these compounds as well as above the forest. We report the measured concentrations of a large number of different VOCs and their oxidation products, such as isoprenoids, organic acids, carbonyls, aromatics, and alcohols. The most prominent VOCs present in air over the last part of the wet season were isoprene, formaldehyde, and formic acid, with mixing ratios of each ranging up to several parts per billion (ppb). Methyl vinyl ketone as well as methacrolein, both oxidation products of isoprene, ranged around 1 ppb. The sum of the measured monoterpene concentrations was below 1 ppb. At the end of the dry season, the amount of C1–C2 organic acids and C1–C2 aldehydes increased significantly up to 17 and 25 ppb, respectively, which is thought to result significantly from vegetation fire emissions. High methanol concentrations also support this scenario. At the same time, however, atmospheric mixing ratios of biogenic compounds such as isoprene increased up to 30 ppb near the crown region and well above 10 ppb at 10–20 m over the forest, whereas monoterpene species seem to decrease. We discuss seasonal development of the vegetation and climatological factors to be responsible for such concentration pattern. The results give an impression about the variability and concentration of VOCs during the different seasons.