Suchergebnisse

8 páginas, 5 figuras, 1 tabla. ; Formaldehyde (FA) is an ubiquitous gas in the atmosphere which reaches notable concentrations in polluted areas and can have great impact on human health. We studied FA exchange between air and two widespread Mediterraneantree species, Quercusilex and Pinushalepensis. Experiments were conducted at the leaf level under laboratory conditions using air from outside the building. In both plant species FA exchange was mainly determined by the atmospheric mixing ratios, with a compensation point calculated around 20 ppbv. Higher values led to uptake and lower values to emission. The second factor that regulated FA exchange was stomatal conductance. FA exchange followed a diurnal cycle with the greatest exchange when stomatal conductance was at maximum. Such stomatal control is consistent with previous studies and is probably due to the high water solubility of FA, resulting in stomatal transpiration being its main exchange pathway. We also observed this relationship between stomatal conductance and FA exchange under conditions of drought and posterior rewatering, in which changes in stomatal conductance were paralleled by changes in FA exchange. Under projected future conditions of enhanced aridity in the Mediterranean, drought-driven limitations of FA exchange may be more relevant. ; Our research was partly supported by ISONET (Marie Curie network contract MC-RTN-CT-2003 504720) from the European Union, by grants CGL2004-01402/BOS and CGL2006-04025/BOS from MEC (Spanish Government), by a grant from the Fundació Abertis, and by a SGR 2005-00312 grant from AGAUR (Generalitat de Catalunya). Roger Seco gratefully acknowledges a FPI fellowship (BES-2005-6989) from MEC. ; Peer reviewed

10 páginas, 4 figuras. ; Several volatile organic compounds (VOCs) have been reported as having a communication role between plants and also between plants and animals. We aimed to test whether methanol, a short-chain oxygenated VOC, could also have a signalling role between plants. We monitored photosynthetic performance and VOC exchange rates of Quercus ilex L. saplings before and after two different treatments: (a) clipping of some leaves to simulate an attack by herbivores and (b) fumigation with gaseous methanol for 5 h to simulate the amount of methanol a plant could receive from surrounding plants if those had been already attacked by herbivores. The clipping treatment enhanced the photosynthetic rates, the chlorophyll a to b ratio and the carotenoid to chlorophyll ratio of nonclipped leaves, suggesting an activation of plant protective metabolism. Also, a small but interesting systemic (in nonclipped leaves) increase in methanol emission rates was observed, which agrees with the possibility that methanol may act as a signalling cue. The methanol fumigation treatment induced an increase in the actual photochemical efficiency of PSII and also in the carotenoid to chlorophyll ratio. Methanol fumigation also promoted a 14% increase in the monoterpene emission rate, 1 day after the treatment, a similar response to the ones induced by other signalling VOCs. The enhanced monoterpene emissions could add to the blend of VOCs emitted after stress and be part of further signalling pathways, thus forwarding the message started by methanol. This study suggests that clipping and methanol fumigation at natural concentrations elicit significant neighbour plant physiological responses and further BVOC emissions. ; This study was supported by the Spanish Government grants CGL2006-04025/BOS, CGL2010-17172, and Consolider-Ingenio Montes CSD2008-00040, the CSIC grant PIF08-006-3 and the Catalan Government grant SGR 2009-458. Roger Seco gratefully acknowledges a FPI fellowship (BES-2005-6989) from MEC (Spanish Government). ; Peer reviewed

43 páginas, 9 figuras, 2 tablas. ; Atmospheric volatile organic compounds (VOCs) are involved in ozone and aerosol generation, thus having implications for air quality and climate. VOCs and their emissions by vegetation also have important ecological roles as they can protect plants from 5 stresses and act as communication cues between plants and between plants and animals. In spite of these key environmental and biological roles, the reports on seasonal and daily VOC mixing ratios in the literature for Mediterranean natural environments are scarce. We conducted seasonal (winter and summer) measurements of VOC mixing ratios 10 in an elevated (720 m a.s.l.) holm oak Mediterranean forest site near the metropolitan area of Barcelona (NE Iberian peninsula). Methanol was the most abundant compound among all the VOCs measured in both seasons. While aromatic VOCs showed almost no seasonal variability, short-chain oxygenated VOCs presented higher mixing ratios in summer, presumably due to greater emission by vegetation and increased photo- 15 chemistry, both enhanced by the high temperatures and solar radiation in summer. Isoprenoid VOCs showed the biggest seasonal change in mixing ratios: they increased by one order of magnitude in summer, as a result of the vegetation's greater physiological activity and emission rates. The maximum diurnal concentrations of ozone increased in summer too, most likely due to more intense photochemical activity and the higher 20 levels of VOCs in the air. The daily variation of VOC mixing ratios was mainly governed by the wind regime of the mountain, as the majority of the VOC species analyzed followed a very similar diel cycle. Mountain and sea breezes that develop after sunrise advect polluted air masses to the mountain. These polluted air masses had previously passed over the urban 25 and industrial areas surrounding the Barcelona metropolitan area, where they were enriched in NOx and in VOCs of biotic and abiotic origin. Moreover, these polluted air masses receive additional biogenic VOCs emitted in the local valley by the vegetation, thus enhancing O3 formation in this forested site. The only VOC species that showed a somewhat different daily pattern were monoterpenes because of their local biogenic emission. Isoprene also followed in part the daily pattern of monoterpenes, but only in summer when its biotic sources were stronger. The increase by one order of magnitude in the concentrations of these volatile isoprenoids highlights the importance of local 5 biogenic summer emissions in these Mediterranean forested areas which also receive polluted air masses from nearby or distant anthropic sources. ; This study was supported by the Spanish Government grants CGL2006- 04025/BOS, CGL2010-17172, Consolider-Ingenio Montes CSD2008-00040 and Accion Com- ´ plementaria DAURE CGL2007-30502-E/CLI, and the Catalan Government grant SGR 2009- 10 458. Roger Seco gratefully acknowledges an FPI fellowship (BES-2005-6989) from the Spanish Government. This research has received funding from the EC Seventh Framework Programme under grant agreement no. 215072 (Marie Curie Initial Training Network, "CLOUD-ITN"). Helpful discussion concerning the PTR-TOF evaluation with Martin Graus and Ralf Schnitzhofer from the Univer- 15 sity of Innsbruck was much appreciated. ; Peer reviewed

17 páginas, 8 figuras. ; PM1 (particulate matter with an aerodynamic diameter <1 µm) non-refractory components and black carbon were measured continuously together with additional air quality and atmospheric parameters at an urban background site in Barcelona, Spain, during March 2009 (campaign DAURE, Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the western Mediterranean). Positive matrix factorization (PMF) was conducted on the organic aerosol (OA) data matrix measured by an aerosol mass spectrometer, on both unit mass (UMR) and high resolution (HR) data. Five factors or sources could be identified: LV-OOA (low-volatility oxygenated OA), related to regional, aged secondary OA; SVOOA (semi-volatile oxygenated OA), a fresher oxygenated OA; HOA (hydrocarbon-like OA, related to traffic emissions); BBOA (biomass burning OA) from domestic heating or agricultural biomass burning activities; and COA (cooking OA). LV-OOA contributed 28 % to OA, SV-OOA 27 %, COA 17 %, HOA 16 %, and BBOA 11 %. The COA HR spectrum contained substantial signal from oxygenated ions (O:C: 0.21) whereas the HR HOA spectrum had almost exclusively contributions from chemically reduced ions (O:C: 0.03). If we assume that the carbon in HOA is fossil while that in COA and BBOA is modern, primary OA in Barcelona contains a surprisingly high fraction (59 %) of non-fossil carbon. This paper presents a method for estimating cooking organic aerosol in ambient datasets based on the fractions of organic mass fragments at m/z 55 and 57: their data points fall into a V-shape in a scatter plot, with strongly influenced HOA data aligned to the right arm and strongly influenced COA data points aligned to the left arm. HR data show that this differentiation is mainly driven by the oxygen-containing ions C3H3O + and C3H5O + , even though their contributions to m/z 55 and 57 are low compared to the reduced ions C4H + 7 and C4H + 9 . A simple estimation method based on the markers m/z 55, 57, and 44 is developed here and allows for a first-order-estimation of COA in urban air. This study emphasizes the importance of cooking activities for ambient air quality and confirms the importance of chemical composition measurements with a high mass and time resolution. ; We thank the organizers of the DAURE project, including Mar Viana and everybody else at ICTJA for their work and help. We acknowledge the CCES project IMBALANCE and the EU-FP7 project EUCAARI for financial support and 'Accion Complementaria DAURE' from the Spanish Ministry of Science and Innovation (CGL2007-30502-E/CLI) for infrastructure support. P. F. DeCarlo is grateful for the postdoctoral support from the US-NSF (IRFP# 0701013). J. Penuelas and R. Seco were sup- ˜ ported by the Spanish Government projects CGL2010-17172 and Consolider Ingenio Montes CSD2008-00040, and by a postdoctoral grant from Fundacion Ram ´ on Areces to R. Seco. The National ´ Center for Atmospheric Research is sponsored by the National Science Foundation. J. L. Jimenez was supported by NSF ATM- 0919189 and DOE (BER, ASR program) DE-FG02-11ER65293. ; Peer reviewed