Showing papers by "Arnoud Apituley published in 2009"

Exploring the relation between aerosol optical depth and PM 2.5 at Cabauw, the Netherlands

Abstract: To acquire daily estimates of PM2.5 distributions based on satellite data one depends critically on an established relation between AOD and ground level PM2.5. In this study we aimed to experimentally establish the AOD-PM2.5 relationship for the Netherlands. For that purpose an experiment was set-up at the AERONET site Cabauw. The average PM 2.5 concentration during this ten month study was 18 μg/m 3, which confirms that the Netherlands are characterised by a high PM burden. A first inspection of the AERONET level 1.5 (L1.5) AOD and PM2.5 data at Cabauw showed a low correlation between the two properties. However, after screening for cloud contamination in the AERONET L1.5 data, the correlation improved substantially. When also constraining the dataset to data points acquired around noon, the correlation between AOD and PM2.5 amounted to R2=0.6 for situations with fair weather. This indicates that AOD data contain information about the temporal evolution of PM2.5. We had used LIDAR observations to detect residual cloud contamination in the AERONET L1.5 data. Comparison of our cloud-screed L1.5 with AERONET L2 data that became available near the end of the study showed favorable agreement. The final relation found for Cabauw is PM 2.5=124.5*AODĝ€"0.34 (with PM2.5 in μg/m3) and is valid for fair weather conditions. The relationship determined between MODIS AOD and ground level PM2.5 at Cabauw is very similar to that based on the much larger dataset from the sun photometer data, after correcting for a systematic overestimation of the MODIS data of 0.05. We applied the relationship to a MODIS composite map to assess the PM2.5 distribution over the Netherlands. Spatial dependent systematic errors in the MODIS AOD, probably related to variability in surface reflectance, hamper a meaningful analysis of the spatial distribution of PM2.5 using AOD data at the scale of the Netherlands.

NO2 lidar profile measurements for satellite interpretation and validation

Abstract: [1] Satellite instruments are efficient detectors of air pollutants such as NO2. However, the interpretation of satellite retrievals is not a trivial matter. We describe a novel instrument, the RIVM NO2 mobile lidar, to measure tropospheric NO2 profiles for the interpretation and validation of satellite data. During the DANDELIONS campaign in 2006 we obtained an extensive collection of lidar NO2 profiles, coinciding with OMI and SCIAMACHY overpasses. On clear days and early mornings a comparison between lidar and in situ measurements showed excellent agreement. At other times the in situ monitors with molybdenum converters suffered from NOy interference. The lidar NO2 profiles indicated a well-mixed boundary layer, with high NO2 concentrations in the boundary layer and concentrations above not differing significantly from zero. The boundary layer concentrations spanned a wide range, which likely depends on the wind directions and on the intensity of local (rush hour) traffic which varies with the day of the week. Large diurnal differences were mainly driven by the height of the boundary layer, although direct photolysis or photochemical processes also contribute. Small-scale temporal and spatial variations in the NO2 concentrations of the order of 20–50% were measured, probably indicative of small-scale eddies. A preliminary comparison between satellite and lidar data shows that the satellite data tend to overestimate the amount of NO2 in the troposphere compared to the lidar data.

Performance Assessment and Application of Caeli — A high-performance Raman lidar for diurnal profiling of Water Vapour, Aerosols and Clouds

Abstract: Caeli is the CESAR Water Vapour, Aerosol and Cloud Lidar and is a multiwavelength, high-performance Raman lidar, capable of providing round-the-clock measurements. It is deployed at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands (51 58’N, 4 56’E). The instrument was developed as a key instrument for CESAR to strengthen the sites capabilities as a profiling station for atmospheric research and climate studies. Next to the lidar, other profiling techniques also routinely operated provide synergy in observations. Since the deployment at CESAR in May 2008, Caeli contributes to observation programmes and studies. The instrument is part of EARLINET, has provided data during the IMPACT and CINDI campaigns and provides correlative measurements for CALIPSO. Recently, the instrument was compared to its peers in the EARLINET Reference Lidar Intercomparison (EARLI09) in Leipzig. This paper describes the Caeli instrument configuration and shows examples of application of the data. Also, preliminary intercomparison results are shown from EARLI09.

EARLINET coordinated lidar observations of Saharan dust events on continental scale

Abstract: EARLINET, the European Aerosol Research Lidar Network, is the best tool to investigate the horizontal and vertical transport of aerosols over Europe. Within the network, particular attention is devoted to Saharan dust events monitoring. An alert system has been established in order to perform devoted measurements in case of intrusions of desert particles on European continent. Starting from data collected within EARLINET since May 2000, a first statistical analysis of the aerosol vertical distribution on European scale during Saharan dust outbreaks, has been performed. These results highlights the fundamental role that EARLINET can have for the study of impact of Saharan dust on European scale. The current 5-year EU project EARLINET-ASOS, started in March 2006, will enhance the operation of the network through the improvement of the instruments and of the temporal coverage, and of the data analysis procedures.

Earli09 - direct intercomparison of eleven earlinet lidar systems

Abstract: Eleven EARLINET lidar systems were directly compared during EARLI09 in Leipzig, Germany, in may, 2009. The measurement and signal comparison strategies are presented and some examples shown.

Analysis of the EARLINET correlative measurements for CALIPSO

Abstract: Lidar techniques represent the most suitable tool to obtain information on the aerosol vertical distribution and therefore to close this kind of observational gap. Lidar networks are fundamental to study aerosol on large spatial scale and to investigate transport and modification phenomena. These are the motivations why EARLINET, the European Aerosol Research Lidar Network, was established in 2000. At present, EARLINET consists of 25 lidar stations: 7 single backscatter lidar stations, 9 Raman lidar stations with the UV Raman channel for independent measurements of aerosol extinction and backscatter, and 9 multiwavelength Raman lid ar stations (elastic channel at 1064 nm, 532 nm, 355 nm, Raman channels at 532 nm and 355 nm, plus depolarization channel at 532 nm) for the retrieval of aerosol microphysical properties. EARLINET data can significantly contribute to the quantifica tion of aerosol concentrations, radiative properties, long-range transport and budget, and prediction of future trends on European and global scale. It can also contribute to improve model treatment on a wide range of scales and to a better exploitation of present and future satellite data. EARLINET is playing an important role in the validation and in the full exploitation of the CALIPSO mission. EARLINET started correlative measurements for CALIPSO si nce June 2006. A strategy for correlative measurements has been defined on the base of the analysis of the high re solution ground track data provid ed by NASA. Results in terms of comparisons between EARLINET and available CALIPSO pr oducts, both level 1 and level 2 data, are presented. Keywords: Lidar, aerosol, clouds, EARLINET, CALIPSO

Coordinated lidar observations of Saharan dust over Europe in the frame of EARLINET-ASOS project during CALIPSO overpasses: A strong dust case study analysis with modeling support

Abstract: Coordinated lidar observations of Saharan dust over Europe are performed in the frame of the EARLINET-ASOS (2006-2011) project, which comprises 25 stations: 16 Raman lidar stations, including 8 multi-wavelength (3+2 station) Raman lidar stations, are used to retrieve the aerosol microphysical properties. Since the launch of CALIOP, the two-wavelength lidar on board the CALIPSO satellite (June 2006) our lidar network has been performing correlative aerosol measurements during CALIPSO overpasses over the individual stations. In our presentation, we report on the correlative measurements obtained during Saharan dust intrusions in the period from June 2006 to June 2008. We found that the number of dust events is generally greatest in late spring, summer and early autumn periods, mainly in southern and south-eastern Europe. A measurement example is presented that was analyzed to show the potential of a ground based lidar network to follow a dust event over a specific study area, in correlation with the CALIOP measurements. The dust transport over the studied area was simulated by the DREAM forecast model. Cross-section analyses of CALIOP over the study area were used to assess the model performance for describing and forecasting the vertical and horizontal distribution of the dust field over the Mediterranean. Our preliminary results can be used to reveal the importance of the synergy between the CALIOP measurement and the dust model, assisted by ground-based lidars, for clarifying the overall transport of dust over the European continent.

Long-term aerosol and cloud database from space-borne lidar and ground-based lidar network observations

Abstract: In June 2006, the satellite-borne lidar CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) began its observations onboard CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations; Winker et al., 2007). This date is regarded the starting point of a unique long-term, global, 4-dimensional aerosol and cloud data set. The forthcoming missions ADM-Aeolus (Atmospheric Dynamics Mission; Stoffelen et al., 2005; Ansmann et al., 2006) of the European Space Agency ESA and EarthCARE (Earth Clouds, Aerosols, and Radiation Explorer) of ESA and the Japan Aerospace Exploration Agency JAXA (ESA, 2004), with their lidar instruments ALADIN (Atmospheric Laser Doppler Lidar Instrument) and ATLID (Atmospheric Lidar), respectively, will continue such kind of observations. It is expected that the long-term data set gained in this way will substantially improve our knowledge on the role of aerosols and clouds in the Earth's climate system.

EARLINET: the European Aerosol Research Lidar Network for the Aerosol Climatology on Continental Scale

Abstract: Lidar techniques represent the most suitable tool to obtain information on the aerosol vertical distribution and therefore to close this kind of observational gap Lidar networks are fundamental to study aerosol on large spatial scale and to investigate transport and modification phenomena These are the motivations why EARLINET, the European Aerosol Research Lidar Network, was established in 2000, as a research program funded by the European Commission in the frame of the 5th framework program After the end of the project, the network activity continued on the base of a voluntary association At present, EARLINET consists of 25 lidar stations distributed over Europe On March 2006, the EC Project EARLINET‐ASOS (Advanced Sustainable Observation System) started on the base of the EARLINET infrastructure This infrastructure project will enhance the operation of the network EARLINET data can contribute significantly to the quantification of aerosol concentrations, radiative properties, long‐range transpor

Sensing the Troposphere from Space

Abstract: The growth of human population and the industrialisation in the 19th and 20th century has led to dramatic changes in the Earth System. The chemical composition of the lowest part of the atmosphere, the troposphere, is changing as a result of human activities. The Earth has entered the "Anthropocene" epoch, where the activities of humans play a key role in air quality and climate change. The rapid development of megacities (see Figure 1) and the strong development in the Asian countries are clear examples of rapid changes that affected the atmosphere in the last decades and will continue to do so in the future. For understanding climate change and air quality, global changes in the chemical composition of the troposphere need to be taken into account/addressed. Especially the global inventory of emission sources play a key role in understanding and modelling the troposphere in relation to climate change and air pollution. Also regional and long-range transport of pollution, as well as the rapid development of pollution levels during the day, are important for understanding air quality and climate change and their interaction Atmospheric measurements from space started in the 70th’s with US sensors SBUV[)] and TOMS[2], focussing on the ozone layer residing in the higher layers in the atmosphere. Sensing the lower atmospheric layers from space is a recent development in satellite remote sensing, where SCIAMACHY[[3]] on board ESA’s ENVISAT), OMI[4] on board NASA’s EOS-Aura) and GOME-2[5] (on board METOP-1) instruments play a leading role. Unprecedented measurements from space from OMI reveal tropospheric pollution maps on a daily basis with urban scale resolution. Measurements from Thermal Infrared instruments like MOPITT [6], AIRS[7] , IASI[[8]] and TES[[9]] also provide unique information on the troposphere, providing tropospheric profile information. In this paper an overview will be given of satellite measurements from space of the chemical composition of the troposphere and their role in climate change and air pollution. Also challenges and future developments for tropospheric measurements from space will be discussed, including the Dutch initiative satellite instrument (TROPOMI) for detection of the tropospheric composition.