ALBERT

Description: At the end of 2015, a CO2/CH4/CO cavity ring-down spectrometer (CRDS) was installed at the Izaña Global Atmosphere Watch (GAW) station (Tenerife, Spain) to improve the Izaña Greenhouse Gases GAW Measurement Programme, and to guarantee the renewal of the instrumentation and the long-term maintenance of this program. We present the results of the CRDS acceptance tests, the raw data processing scheme applied, and the response functions used. Also, the calibration results, the implemented water vapor correction, the target gas injection statistics, the ambient measurements performed from December 2015 to July 2017, and their comparison with other continuous in situ measurements are described. The agreement with other in situ continuous measurements is good most of the time for CO2 and CH4, but for CO it is just outside the GAW 2 ppb objective. It seems the disagreement is not produced by significant drifts in the CRDS CO World Meteorological Organization (WMO) tertiary standards. The more relevant contributions of the present article are (1) determination of linear relationships between flow rate, CRDS inlet pressure, and CRDS outlet valve aperture; (2) determination of a slight CO2 correction that takes into account changes in the inlet pressure/flow rate (as well as its stability over the years), and attributing it to the existence of a small spatial inhomogeneity in the pressure field inside the CRDS cavity due to the gas dynamics; (3) drift rate determination for the pressure and temperature sensors located inside the CRDS cavity from the CO2 and CH4 response function drift trends; (4) the determination of the H2O correction for CO has been performed using raw spectral peak data instead of the raw CO provided by the CRDS and using a running mean to smooth random noise in a long water-droplet test (12 h) before performing the least square fit; and (5) the existence of a small H2O dependence in the CRDS flow and of a small spatial inhomogeneity in the temperature field inside the CRDS cavity are pointed out and their origin discussed.

Description: Iodine monoxide (IO) differential slant column densities (DSCD) have been retrieved from a new multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument deployed at the Izaña subtropical observatory as part of the Network for the Detection of Atmospheric Composition Change (NDACC) programme. The station is located at 2370 m a.s.l., well above the trade wind inversion that limits the top of the marine boundary layer, and hence is representative of the free troposphere. We report daily observations from May to August 2010 at different viewing angles. During this period, the spectral signature of IO was unequivocally detected on every day of measurement. A mean IO DSCD of 1.52×1013 molecules cm−2 was observed at the 5° instrument elevation angle (IEA) on clear days using a single zenith reference for the reported period, with a day-to-day variability of 33% at one standard deviation. Based on the simulation of the DSCDs using radiative transfer calculations with five different hypothesized IO profiles, the IO mixing ratio is estimated to range between 0.2 and 0.4 pptv in the free troposphere. Episodes of Saharan dust outbreaks were also observed, with large increases in the DSCDs at higher IEA, suggesting an enhancement of IO inside the dust cloud.

Description: In this work, a reconstruction of climatic conditions in Andalusia (southern Iberian Peninsula) during the period 1701–1850, as well as an evaluation of its associated uncertainties, is presented. This period is interesting because it is characterized by a minimum in solar irradiance (Dalton Minimum, around 1800), as well as intense volcanic activity (for instance, the eruption of Tambora in 1815), at a time when any increase in atmospheric CO2 concentrations was of minor importance. The reconstruction is based on the analysis of a wide variety of documentary data. The reconstruction methodology is based on counting the number of extreme events in the past, and inferring mean value and standard deviation using the assumption of normal distribution for the seasonal means of climate variables. This reconstruction methodology is tested within the pseudoreality of a high-resolution paleoclimate simulation performed with the regional climate model MM5 coupled to the global model ECHO-G. The results show that the reconstructions are influenced by the reference period chosen and the threshold values used to define extreme values. This creates uncertainties which are assessed within the context of climate simulation. An ensemble of reconstructions was obtained using two different reference periods (1885–1915 and 1960–1990) and two pairs of percentiles as threshold values (10–90 and 25–75). The results correspond to winter temperature, and winter, spring and autumn rainfall, and they are compared with simulations of the climate model for the considered period. The mean value of winter temperature for the period 1781–1850 was 10.6 ± 0.1 °C (11.0 °C for the reference period 1960–1990). The mean value of winter rainfall for the period 1701–1850 was 267 ± 18 mm (224 mm for 1960–1990). The mean values of spring and autumn rainfall were 164 ± 11 and 194 ± 16 mm (129 and 162 mm for 1960–1990, respectively). Comparison of the distribution functions corresponding to 1790–1820 and 1960–1990 indicates that during the Dalton Minimum the frequency of dry and warm (wet and cold) winters was lower (higher) than during the reference period: temperatures were up to 0.5 °C lower than the 1960–1990 value, and rainfall was 4% higher.

Description: In this work, a reconstruction of climatic conditions in Andalusia (southern Iberia Peninsula) during the period 1701–1850, as well as an evaluation of its associated uncertainties, is presented. This period is interesting because it is characterized by a minimum in the solar irradiance (Dalton Minimum, around 1800), as well as intense volcanic activity (for instance, the eruption of the Tambora in 1815), when the increasing atmospheric CO2 concentrations were of minor importance. The reconstruction is based on the analysis of a wide variety of documentary data. The reconstruction methodology is based on accounting the number of extreme events in past, and inferring mean value and standard deviation using the assumption of normal distribution for the seasonal means of climate variables. This reconstruction methodology is tested within the pseudoreality of a high-resolution paleoclimate simulation performed with the regional climate model MM5 coupled to the global model ECHO-G. Results show that the reconstructions are influenced by the reference period chosen and the threshold values used to define extreme values. This creates uncertainties which are assesed within the context of the climate simulation. An ensemble of reconstructions was obtained using two different reference periods and two pairs of percentiles as threshold values. Results correspond to winter temperature, and winter, spring, and autumn rainfall, and they are compared with simulations of the climate model for the considered period. The comparison of the distribution functions corresponding to 1790–1820 and 1960–1990 periods indicates that during the Dalton Minimum the frequency of dry and warm (wet and cold) winters was lesser (higher) than during the reference period. In spring and autumn it was detected an increase (decrease) in the frequency of wet (dry) seasons. Future research challenges are outlined.

Description: At the end of 2015, a CO2/CH4/CO Cavity Ring-Down Spectrometer (CRDS) was installed at the Izaña Global Atmosphere Watch station (Tenerife, Spain) to improve the Izaña Greenhouse gases GAW measurement programme, and to guarantee the renewal of the instrumentation and the long-term maintenance of this programme. We present the results of the CRDS acceptance tests, the processing of raw data applied through novel numerical codes, and the response functions used. Also, the calibration results, the implemented water vapour correction, the target gas injection statistics, the ambient measurements performed from December 2015 to July 2017, and their comparison with other continuous in situ measurements are described. The agreement with other in situ continuous measurements is good most of the time for CO2 and CH4, but for CO is just outside the GAW 2-ppb objective. It seems the disagreement is not produced by significant drifts in the CRDS CO WMO tertiary standards. The main novelties are: 1) determination of a slight CO2 correction that takes into account changes in the inlet pressure/flow rate; 2) detailed justification of the use of virtual tanks to monitor the response function changes in time; 3) drift rate determination for the pressure and temperature sensors located inside the CRDS cavity; 4) novelties in the determination of the H2O correction for CO; and 5) determination and discussion of the origin of the CRDS-flow inlet pressure and H2O dependences.

Description: An unprecedented extreme Saharan dust event was registered in winter time from 20 to 23 February 2017 over the Iberian Peninsula (IP). We report on aerosol optical properties observed under this extreme dust outbreak through remote sensing (active and passive) techniques. For that, EARLINET (European Aerosol Research LIdar NETwork) lidar and AERONET (AErosol RObotic NETwork) Sun-photometer Cimel CE 318 measurements are used. The sites considered are: Barcelona (41.38ºN, 2.17ºE), Burjassot (39.51ºN, 0.42ºW), Cabo da Roca (38.78ºN, 9.50ºW), Évora (38.57ºN, 7.91ºW), Granada (37.16ºN, 3.61ºW) and Madrid (40.45ºN, 3.72ºW). In general, large aerosol optical depths (AOD) and low Ångström exponents (AE) are observed. An AOD of 2.0 at 675nm is reached in several stations. Maximum values of AOD675 of 2.5 are registered in Évora. During and around the peak of AOD675, AEs close to 0 are measured. With regard to vertically-resolved aerosol optical properties, particle backscatter coefficients as high as 1.5∙10−5m−1sr−1 at 355nm are recorded at every lidar stations. Mean lidar ratios are found in the range 40–55sr at 355nm and 34–61sr at 532nm during the event inside the dust layer. Mean particle and volume depolarization ratios are found to be very consistent between lidar stations. They range 0.19–0.31 and 0.12–0.26 respectively. The optical properties are also found very stable with height in the dust layer. Another remarkable aspect of the event is the limited height of the dust transport which is found between the ground and 5km. Our vertically-resolved aerosol properties are also used to estimate the performances of two dust models, namely BSC-DREAM8b and NMMB/BSC-Dust, in order to evaluate their forecast skills in such intense dust outbreaks. We found that forecasts provided by the NMMB/BSC-Dust show a better agreement with observations than the ones from BSC-DREAM8b. The BSC-DREAM8b forecasts (24h) present a large underestimation during the event. No clear degradation of the prognostics is appreciated in 24, 48, 72h except for the Barcelona station.

Description: Atmospheric CO in-situ measurements are carried out at the Izaña (Tenerife) global GAW mountain station using a RGA (Reduction Gas Analyser). In-situ measurements at Izaña are representative of the subtropical North-East Atlantic free troposphere, specially during the night period. We present the measurement system configuration, the response function, the calibration scheme, the data processing, the Izaña's 2008–2011 CO nocturnal time series, and the mean diurnal cycle by months. We have developed a rigorous uncertainty analysis for carbon monoxide measurements carried out at the Izaña station which could be applied to other GAW stations. We determine the combined standard uncertainty from four components of the measurement: uncertainty of the WMO standard gases interpolated over the range of measurement, the uncertainty that takes into account the agreement between the standard gases and the response function used, the uncertainty due to the repeatability of the injections, and the propagated uncertainty related to the response function parameters uncertainties (which also takes into account the covariance between the parameters). The mean value of the combined standard uncertainty decreased significantly after March 2009, from 2.37 nmol mol−1 to 1.66 nmol mol−1, due to improvements in the measurement system. A fifth type of uncertainty we call representation uncertainty is considered when some of the data necessary to compute exactly the mean are absent. Any computed mean has also a propagated uncertainty arising from the uncertainties of the data used to compute the mean. The law of propagation depends on the type of uncertainty component (random or systematic). In-situ hourly means are compared with simultaneous and collocated NOAA flask samples. The uncertainty in the differences is determined and whether these are significant. For 2009–2011, only 24.5% of the differences are significant, and 68% of the differences are between −2.39 and 2.5 nmol mol−1. Total and annual mean differences are computed using conventional expressions but also expressions with weights based on the minimum variance method. The annual mean differences for 2009–2011 are well within the ±2 nmol mol−1 compatibility goal of GAW.

Description: Atmospheric CO in situ measurements are carried out at the Izaña (Tenerife) global GAW (Global Atmosphere Watch Programme of the World Meteorological Organization – WMO) mountain station using a Reduction Gas Analyser (RGA). In situ measurements at Izaña are representative of the subtropical Northeast Atlantic free troposphere, especially during nighttime. We present the measurement system configuration, the response function, the calibration scheme, the data processing, the Izaña 2008–2011 CO nocturnal time series, and the mean diurnal cycle by months. We have developed a rigorous uncertainty analysis for carbon monoxide measurements carried out at the Izaña station, which could be applied to other GAW stations. We determine the combined standard measurement uncertainty taking into consideration four contributing components: uncertainty of the WMO standard gases interpolated over the range of measurement, the uncertainty that takes into account the agreement between the standard gases and the response function used, the uncertainty due to the repeatability of the injections, and the propagated uncertainty related to the temporal consistency of the response function parameters (which also takes into account the covariance between the parameters). The mean value of the combined standard uncertainty decreased significantly after March 2009, from 2.37 nmol mol−1 to 1.66 nmol mol−1, due to improvements in the measurement system. A fifth type of uncertainty we call representation uncertainty is considered when some of the data necessary to compute the temporal mean are absent. Any computed mean has also a propagated uncertainty arising from the uncertainties of the data used to compute the mean. The law of propagation depends on the type of uncertainty component (random or systematic). In situ hourly means are compared with simultaneous and collocated NOAA flask samples. The uncertainty of the differences is computed and used to determine whether the differences are significant. For 2009–2011, only 24.5% of the differences are significant, and 68% of the differences are between −2.39 and 2.5 nmol mol−1. Total and annual mean differences are computed using conventional expressions but also expressions with weights based on the minimum variance method. The annual mean differences for 2009–2011 are well within the ±2 nmol mol−1 compatibility goal of GAW.

Description: Historically, the study of dredging processes has depended on physical laboratory tests. The IH-Dredge model has been developed to simulate these processes numerically. It simulates the evolution of the seabed, sediment and toxic substances involved in dredging operations. The model has been calibrated and validated with experimental data, and it has been applied in a dredging operation in the Port of Marin, Spain.

Description: Dry–rewetting perturbations are natural disturbances in the edaphic environment and particularly in dryland cultivation areas. The interaction of this disturbance with glyphosate-based herbicides (GBHs) deserves special attention in the soil environment due to the intensification of agricultural practices and the acceleration of climate change with an intensified water cycle. The objective of this study was to assess the response of microbial communities in a soil with a long history of GBHs to a secondary imposed perturbation (a single dry–rewetting event). A factorial microcosm study was conducted to evaluate the potential conditioning effect of an acute glyphosate exposure on the response to a following dry–rewetting event. A respiratory quotient (RQ) based on an ecologically relevant substrate (p-coumaric acid) and basal respiration was used as a physiological indicator. Similarly, DNA-based analyses were considered, including quantitative PCR (qPCR) of functional sensitive microbial groups linked to cycles of carbon (Actinobacteria) and nitrogen (ammonia-oxidizing microorganisms), qPCR of total bacteria and denaturing gradient gel electrophoresis (DGGE) of ammonia-oxidizing bacteria (AOB). Significant effects of herbicide and of dry–rewetting perturbations were observed in the RQ and in the copy number of the amoA gene of AOB, respectively. However, no significant interaction was observed between them when analyzing the physiological indicator and the copy number of the evaluated genes. PCR–DGGE results were not conclusive regarding a potential effect of dry–rewetting × herbicide interaction on AOB community structure, suggesting further analysis by deep sequencing of the amoA gene. The results of this study indicate that the perturbation of an acute glyphosate exposure in a soil with a long history of this herbicide does not have a conditioning effect on the response to a subsequent dry–rewetting disturbance according to a physiological indicator or the quantified bacterial/archaeal genes. This is particularly relevant for the sustainability of soils in rainfed agriculture, where frequent exposure to GBHs along with intensification of hydrological cycles are expected to occur. Further studies considering multiple dry–rewetting disturbances and in different soil types should be conducted to simulate those conditions and to validate our results.