29 research outputs found
Measurements of total ozone amount over Badajoz (Southwestern Spain) by means of a GUV multiband radiometer
The Ultraviolet Index (UVI) obtained by a multichannel radiometer GUVâ2511 (Biospherical Instruments Inc.) is analyzed in this paper. This instrument has been recently installed in the radiometric station of Extremadura University in Badajoz (Spain). The UV Index has been calculated by a linear combination of three and four GUV channel irradiance values. In order to test these results, simultaneous values of UVI were calculated with the data provided by a well calibrated broadband UVSâEâT instrument colocated side by side the GUV multichannel. This radiometer has a spectral response that is adapted to the erythemal (sunburn) action spectrum of the human skin. Oneâminute simultaneous values of both instruments have been used to calculate ultraviolet Index (UVI). Although the measurement period is limited, it covers all sky conditions, from cloudâfree to overcast days. UVI calculated with the whole data set by both methods are well correlated, but not as well as using only clear day data. It was observed that GUV underestimates UVI values (mean bias error, MBE=18.9%), being the four channel method the most successful
Counteracting gradients of light and soil nutrients in the understorey of Mediterranean oak forests.
The forest canopy modifies the availability of resources (light, water, and soil nutrients)
in the understorey. In this paper we analyze the relationships between woody canopy
density, litter accumulation, and topsoil N and P availability in the understorey of two
oak forests: one in southern Portugal and the other in southern Spain. Both forests
persist on low-nutrient soils, particularly poor in P. We hypothesize that direct and
indirect effects of the canopy overstorey cause opposite gradients in the availability of
essential resources (light and key soil nutrients) in the understorey. In both studied
forests we found significant relationships between the overall canopy density, light availability,
topsoil litter accumulation, and the availability of N and P, which frequently
limit plant growth. Path analysis (by Shipleyâs d-sep method) showed that the available
data were consistent with the proposed causal model. The average values of soil variables
at the end quartiles of the light-availability gradient were compared. Results showed
large differences in litter accumulation (~30Ă) and available-N and -P topsoil concentrations
(~3Ă) in the Spanish forest (with the wider environmental gradient). Furthermore,
P increased from the âvery lowâ range to the âlowâ or even the âoptimumâ range of
availability (according to standard plant growth criteria), which suggests potential effects
on the growth of the understorey plant species. We conclude that the counteracting
gradients of the essential resources -light and nutrients- in the forest understorey
resulted from direct and indirect effects of the canopy overstorey, respectively. We suggest
that these counteracting effects of the woody canopy on essential resources of different
nature must be considered when interpreting the patterns of understorey plant populations
and communities.The spanish MEC (CGL2005-05830-C03-01-BOS, DINAMED project) and the Portuguese FCT(SFRH/BD/8322/2002 grant to SMM)supported the research.Peer reviewe
Synergistic HNO3-H2SO4-NH3 upper tropospheric particle formation
New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN)(1-4). However, the precursorvapoursthat drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we showthat nitric acid, sulfuric acid and ammonia form particles synergistically, at ratesthat are orders of magnitude faster than those from any two ofthe three components. The importance ofthis mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the uppertroposphere overthe Asian monsoon region(5,6). Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements showthat these CCN are also highly efficient ice nucleating particles-comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO3-H2SO4-NH3 nucleation in the uppertroposphere and producing ice nucleating particles that spread acrossthe mid-latitude Northern Hemisphere.Peer reviewe
An intercomparison study of four different techniques for measuring the chemical composition of nanoparticles
Currently, the complete chemical characterization of nanoparticles (<â100ânm) represents an analytical challenge, since these particles are abundant in number but have negligible mass. Several methods for particle-phase characterization have been recently developed to better detect and infer more accurately the sources and fates of sub-100ânm particles, but a detailed comparison of different approaches is missing. Here we report on the chemical composition of secondary organic aerosol (SOA) nanoparticles from experimental studies of α-pinene ozonolysis at â50, â30, and â10ââC and intercompare the results measured by different techniques. The experiments were performed at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). The chemical composition was measured simultaneously by four different techniques: (1) thermal desorptionâdifferential mobility analyzer (TDâDMA) coupled to a NO chemical ionizationâatmospheric-pressure-interfaceâtime-of-flight (CIâAPiâTOF) mass spectrometer, (2) filter inlet for gases and aerosols (FIGAERO) coupled to an I high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS), (3) extractive electrospray Na ionization time-of-flight mass spectrometer (EESI-TOF), and (4) offline analysis of filters (FILTER) using ultra-high-performance liquid chromatography (UHPLC) and heated electrospray ionization (HESI) coupled to an Orbitrap high-resolution mass spectrometer (HRMS). Intercomparison was performed by contrasting the observed chemical composition as a function of oxidation state and carbon number, by estimating the volatility and comparing the fraction of volatility classes, and by comparing the thermal desorption behavior (for the thermal desorption techniques: TDâDMA and FIGAERO) and performing positive matrix factorization (PMF) analysis for the thermograms. We found that the methods generally agree on the most important compounds that are found in the nanoparticles. However, they do see different parts of the organic spectrum. We suggest potential explanations for these differences: thermal decomposition, aging, sampling artifacts, etc. We applied PMF analysis and found insights of thermal decomposition in the TDâDMA and the FIGAERO
Measurement of the collision rate coefficients between atmospheric ions and multiply charged aerosol particles in the CERN CLOUD chamber
Aerosol particles have an important role in Earth's
radiation balance and climate, both directly and indirectly through
aerosolâcloud interactions. Most aerosol particles in the atmosphere are
weakly charged, affecting both their collision rates with ions and neutral
molecules, as well as the rates by which they are scavenged by other aerosol
particles and cloud droplets. The rate coefficients between ions and aerosol
particles are important since they determine the growth rates and lifetimes
of ions and charged aerosol particles, and so they may influence cloud
microphysics, dynamics, and aerosol processing. However, despite their
importance, very few experimental measurements exist of charged aerosol
collision rates under atmospheric conditions, where galactic cosmic rays in
the lower troposphere give rise to ion pair concentrations of around 1000âcmâ3. Here we present measurements in the CERN CLOUD chamber of the
rate coefficients between ions and small (<10ânm) aerosol particles
containing up to 9 elementary charges, e. We find the rate coefficient of a
singly charged ion with an oppositely charged particle increases from 2.0
(0.4â4.4)âĂâ10â6âcm3âsâ1 to 30.6 (24.9â45.1)âĂâ10â6âcm3âsâ1 for particles with charges of 1 to
9âe, respectively, where the parentheses indicate the ±1Ï
uncertainty interval. Our measurements are compatible with theoretical
predictions and show excellent agreement with the model of
Gatti and Kortshagen (2008).</p
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High Gas-Phase Methanesulfonic Acid Production in the OH-Initiated Oxidation of Dimethyl Sulfide at Low Temperatures
Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, H2SO4). Despite their importance, accurate prediction of MSA and H2SO4from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to -10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while H2SO4production is modestly affected. This leads to a gas-phase H2SO4-to-MSA ratio (H2SO4/MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CH3S(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2-10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NOxeffect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase H2SO4/MSA measurements
High Gas-Phase Methanesulfonic Acid Production in the OH-Initiated Oxidation of Dimethyl Sulfide at Low Temperatures
Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, HSO). Despite their importance, accurate prediction of MSA and HSO from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to â10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while HSO production is modestly affected. This leads to a gas-phase HSO-to-MSA ratio (HSO/MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CHS(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2â10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NO effect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase HSO/MSA measurements
Synergistic HNOâHSOâNH upper tropospheric particle formation
New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN). However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region5,6. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particlesâcomparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNOâHSOâNH nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere
High Gas-Phase Methanesulfonic Acid Production in the OH-Initiated Oxidation of Dimethyl Sulfide at Low Temperatures
Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, H2SO4). Despite their importance, accurate prediction of MSA and H2SO4from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to -10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while H2SO4production is modestly affected. This leads to a gas-phase H2SO4-to-MSA ratio (H2SO4/MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CH3S(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2-10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NOxeffect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase H2SO4/MSA measurements.Peer reviewe