Klaus Schaefer

• Dr. sc. nat.
• Professor at Chengdu University of Information Technology

Because of the worldwide growth in air traffic and its increasing effects on the atmospheric environment, it is necessary to quantify the direct aircraft emissions at all altitudes. In this study Fourier-transform infrared emission spectroscopy as a remote-sensing multi-component-analyzing technique for aircraft exhausts was investigated at ground...

Soils represent a major global source and sink of greenhouse gases (GHGs). Many studies of GHG fluxes between soil, plant and atmosphere rely on chamber measurements. Different chamber techniques have been developed over the last decades, each characterised by different requirements and limitations. In this manuscript, we focus on the non‐steady‐st...

This review provides a community's perspective on air quality research focusing mainly on developments over the past decade. The article provides perspectives on current and future challenges as well as research needs for selected key topics. While this paper is not an exhaustive review of all research areas in the field of air quality, we have sel...

T he interdisciplinary „Smart Air Quality Network" (SmartAOnet) project provides an overall system for recording, visualising and predicting the spatial distribution of air pollutant concentrations in urban atmospheres. Within more than three years SmartAOnet aimed to implement an inexpensive measurement network, which is transferable to other citi...

This review provides a community's perspective on air quality research focussing mainly on developments over the past decade. The article provides perspectives on current and future challenges as well as research needs for selected key topics. While this paper is not an exhaustive review of all research areas in the field of air quality, we have se...

The increasing availability of low-cost air quality sensors has led to novel sensing approaches. Distributed networks of low-cost sensors, together with data fusion and analytics, have enabled unprecedented, spatiotemporal resolution when observing the urban atmosphere. Several projects have demonstrated the potential of different approaches for hi...

Land–sea breeze (LSB) is an atmospheric mesoscale circulation that occurs in the vicinity of the coast and is caused by uneven heating resulting from the difference in specific heat capacity between the sea and land surfaces. The circulation structure of LSB was quantitatively investigated with a Doppler wind lidar Windcube100s on the west coast of...

Both PM2.5 and visibility are important physical parameters to measure the air pollution condition. This paper first provided a new normalization approach for the relationship between PM2.5 and visibility in heavy pollutant region, which realized a mathematical calculation for two different physical parameters based on non-dimensional data process...

To investigate the spatial representativeness of mixing layer height (MLH) observations in the North China Plain (NCP), we performed several successive MLH measurements with ceilometers from 2013 to 2017, and the MLH observation data were analyzed at different measurement scales. Daytime MLH differences among stations increased with increasing obse...

The SmartAQnet research project is investigating a smart way of determining the spatial distribution of fine dust, prototyped at a demonstration site in Augsburg, Germany. The research approach is the collection of different qualities of fine dust measurement data and its combination with remote sensing data. Measured fine dust data can be fed into...

The “Berlin Air quality and Ecosystem Research: Local and long-range Impact of anthropogenic and Natural hydrocarbons” (BAERLIN2014) campaign was conducted during the 3 summer months (June–August) of 2014. During this measurement campaign, both stationary and mobile measurements were undertaken to address complementary aims. This paper provides an...

Air quality and the associated subjective and health-related quality of life are among the important topics of urban life in our time. In the past years, a paradigm shift towards integrating mobile PM monitors to form distributed sensing networks has begun in air quality sensing [1]. In addition to new and promising measurement approaches, large-sc...

To investigate the spatiotemporal variability of the mixing layer height (MLH) on the North China Plain (NCP), multi-site and long-term observations of the MLH with ceilometers at three inland stations (Beijing, BJ; Shijiazhuang, SJZ; Tianjin, TJ) and one coastal site (Qinhuangdao) were conducted from 16 October 2013 to 15 July 2015. The MLH of the...

A Single Particle Aerosol Mass Spectrometer (SPAMS) was deployed in the urban area of Chengdu to investigate the size-resolved chemical composition and mixing state of single particles from 22 September to 26 October 2016. Ten major single particle types were resolved with the ART-2a algorithm and these types were classified into carbonaceous parti...

Die räumliche und zeitliche Verteilung von Luftschadstoffen in Städten ist sehr variabel, da sie von unterschiedlichen Einflüssen abhängt, die von den Emittenten (räumliche Anordnung, zeitliche Aktivität) als auch den meteorologischen Bedingungen, der Bebauung und den chemischen Prozessen kommen. Zurzeit werden Verunreinigung der Luft mit relativ w...

Haze pollution by anthropogenic emitted particles is a frequent challenge for Beijing air quality in addition to the well-known dust storm events. Man-made air pollution is able to cause hazy conditions reducing the sight range. Since those air quality conditions became more and more frequent in Beijing recently, this paper focuses on the seasonal...

The Berlin Air quality and Ecosystem Research: Local and long-range Impact of anthropogenic and Natural hydrocarbons (BAERLIN2014) campaign was conducted during the three summer months (June–August) of 2014. During this measurement campaign, both stationary and mobile measurements were undertaken to address complementary aims. This paper provides a...

Urban areas often suffer from high air pollutant concentrations. To study the influence of the mixing layer height (MLH) on concentrations of important pollutants in an urban street canyon of a busy road, a long-term measurement campaign was performed at the kerb site of an arterial road in Essen, Germany, during the winter 2011/2012 and the early...

A continuous daily PM2.5 sampling campaign from 10 April till 8 June 2013, including three haze episodes, was conducted in Beijing. Chemical species, including EC, OC, water-soluble ions and inorganic elements, were analysed by a thermal/optical carbon analyser, IC and ICP-MS, respectively. A comparison of air quality during such haze episodes in r...

Tropospheric ozone and particulate matter affect human health and cause vegetation stress, dysfunction and damages. In this study we investigate the effect of increasing urban vegetation i.e. tree species on atmospheric chemistry, a potential urban management strategy to counteract high levels of local pollutants such as ozone, OH and PM10 caused b...

The mixing layer height (MLH) is a measure for the vertical turbulent exchange within the boundary layer, which is one of the controlling factors for the dilution of pollutants emitted near the ground. Based on continuous MLH measurements with a Vaisala CL51 ceilometer and measurements from an air quality network, the relationship between MLH and n...

The state and composition of the lowest part of the planetary boundary layer (PBL), i.e., the atmospheric surface layer (SL), reflects the interactions of external forcing, land surface, vegetation, human influence and the atmosphere. Vertical profiles of atmospheric variables in the SL at high spatial (meters) and temporal (1 Hz and better) resolu...

Air Quality and with this, subjective and health related life quality, is one of the biggest topics of modern cities and developing countries in our time. For many regions and cities it is difficult to take action regarding air quality in mobility, residential or working areas, because there is no fine-meshed and profound database available for mak...

Augmenting long-term ecosystem-atmosphere observations with multidisciplinary intensive campaigns aims at closing gaps in spatial and temporal scales of observation for energy- and biogeochemical cycling, and at stimulating collaborative research. ScaleX is a collaborative measurement campaign, co-located with a long-term environmental observatory...

To investigate the spatiotemporal variability of regional mixing layer height (MLH) on the North China Plain (NCP), multi-site and long-term observations of MLH with ceilometers at three inland stations [e.g., Beijing (BJ), Shijiazhuang (SJZ), Tianjin (TJ)] and one coastal site [e.g., Qinhuangdao (QHD)] were conducted from 16 October 2013 to 15 Jul...

The design and field performance of a compact diode laser-based instrument for measuring methane on unmanned aerial systems (UAS) is described. The system is based on open-path, wavelength modulation spectroscopy with a 3.27 µm GaSb laser. We design two versions of the sensor for a long-endurance fixed wing UAS and a rotary wing hexacopter, with in...

The state and composition of the lowest part of the planetary boundary layer (PBL), i.e., the atmospheric surface layer (SL), reflects the interactions of external forcing, land surface, vegetation, human influence and the atmosphere. Vertical profiles of atmospheric variables in the SL at high spatial and temporal resolution increase our understan...

Chengdu, the capital of Sichuan Province and the main city in Sichuan basin, is one of the heavily polluted cities in China. The characteristics of single particles in the atmosphere over Chengdu are critical for the in-depth understanding of their sources, formation mechanisms, and effects. In this study, a continuous ambient aerosol measurement w...

The assessment of airborne fine particle composition and secondary pollutant characteristics in the case of Augsburg, Germany, during winter (31 January-12 March 2010) is studied on the basis of aerosol mass spectrometry (3 non-refractory components and organic matter, 3 positive matrix factorizations (PMF) factors), particle size distributions (PS...

Daily mass concentrations and chemical compositions (elemental carbon, organic carbon, water soluble ions, chemical elements and organic species) of PM were measured continuously in Beijing for one year from June 2010 to June 2011 (365 samples). The seasonal variation of PM mass concentration followed the order of spring 2011 > winter 2010 > summer...

The mixing layer is an important meteorological factor that affects air pollution. In this study, the atmospheric mixing layer height (MLH) was observed in Beijing from July 2009 to December 2012 using a ceilometer. By comparison with radiosonde data, we found that the ceilometer underestimates the MLH under conditions of neutral stratification cau...

The improved understanding of the interlinked atmospheric and terrestrial hydrological processes requires concerted and compartment-crossing observation and -modeling efforts. Through the TERENO preAlpine Observatory, located in the southern Bavarian region of Germany, comprehensive technical infrastructure is being established to allow joint analy...

The mixing layer is an important meteorological factor that affects atmospheric pollution. A study of atmospheric pollution in the Beijing area was performed from July 2009 to December 2012, using a ceilometer, to observe and study the atmospheric mixing layer height (MLH). Based on a comparison and validation of multiple types of data, we evaluate...

Mixing layer height (MLH) is a key parameter to determine the influence of meteorological parameters upon air pollutants such as trace gas species and particulate concentrations near the surface. Meteorology, and MLH as a key parameter, affect the budget of emission source strengths, deposition, and accumulation. However, greater possibilities for...

Five portable Bruker EM27/SUN FTIR (Fourier transform infrared) spectrometers have been used for the accurate and precise observation of column-averaged abundances of CO2 and CH4 around the major city Berlin. In the work by Frey et al. (2015), a calibration procedure is developed and applied to the set of spectrometers used for the Berlin campaign....

A comprehensive calibration procedure for mobile, low-resolution, solar-absorption FTIR spectrometers, used for greenhouse gases observations, is developed. These instruments commend themselves for campaign use and deployment at remote sites. The instrumental line shape (ILS) of each spectrometer has been thoroughly characterized by analyzing the s...

Elemental carbon (EC) or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In this study, radiocarbon (14C) based source apportionment is used to distinguish between fossil fuel and biomass burning sources of EC isolated from aerosol filter samples collected in Beijing from June 2010 to May 2011. The 14C r...

Urban air pollution was studied in Beijing, China, in 2009 and in Augsburg, Germany, in 2012 by DOAS, which contains an emitter/receiver unit pointing to three retro-reflectors, to investigate the diurnal and spatial variations of gaseous pollutants like NO, NO2, O-3 and HCHO in a small-scale traffic influenced area. Information about several emiss...

Several low resolution spectrometers were used to investigate the CO2 and CH4 emissions of the megacity Berlin. Before and after the campaign the instruments were tested side-by-side. An excellent level of agreement and stability was found between the different spectrometers: the drifts in XCO2 and XCH4 are within 0.005 and 0.035%, respectively. Th...

Five portable Bruker EM27/SUN FTIR spectrometers have been used for the accurate and precise observation of column averaged abundances of CO2 and CH4 around the megacity Berlin. In the first part of this work (Frey et al., 2015) we have presented the various measures that were undertaken to ensure that the observations are consistent between sites,...

The greening of urban living space is a current goal of many urban planners and campaigns to reduce air pollution for residents. In the city of Berlin, green spaces account for an above-average proportion of the floor area, at over 30%. Thus, vegetation makes an important contribution to exchange flows of trace gases and particles or energy. In ord...

Emission sources as well as wind speed and direction and MLH are important factors which influence high air pollutant concentrations. This is generally known (Schäfer et al., 2006) but the detailed understanding of processes directing certain air pollutant concentrations like HCHO is not complete. To study these processes a long-term campaign in Au...

In 2050 70% of the global population is expected to live in urban areas. Climate change will render these areas more vulnerable to heat waves, which often are accompanied by severe air pollution problems. The Urban Heat Island (UHI) is a feature that adds to the general temperature increase that is expected. Decreasing the UHI would impact air qual...

With the establishment of ceilometer networks by national weather services, a discussion commenced to which extent these simple backscatter lidars can be used for aerosol research. Though primarily designed for the detection of clouds it was shown that at least observations of the vertical structure of the boundary layer might be possible. However,...

With the establishment of ceilometer networks by national weather services a discussion commenced to which extent these simple backscatter lidars can be used for aerosol research. Though primarily designed for the detection of clouds it was shown that at least observations of the vertical structure of the boundary layer might be possible. However,...

As particulate matter (PM) impacts human health, knowledge about its composition, exposure and source apportionment is required. A study of the urban atmosphere in the case of Augsburg, Germany, during winter (31 January-12 March 2010) is thus presented here. Investigations were performed on the basis of aerosol mass spectrometry and further air po...

Air pollution is one of the most significant environmental concerns in China today, particularly in the highly industrialized Eastern Chinese mega cities. During the Olympic Summer Games in 2008, the air pollution in China’s capital city of Beijing became an issue of international interest. Air pollution in Beijing has a number of key constituent c...

An in vitro plasmid scission assay was employed to study the variation of the oxidative capacity of a yearly PM2.5 samples in a residential area of Beijing. A total of 24 PM2.5 samples including 2samples per month (normal weather, fog and haze included) were collected from June 2010 to June 2011.The experimental results showed that toxicity of the...

The main purpose of eye-safe laser ceilometers is regular reporting of cloud base height, vertical visibility, and cloud cover. These instruments operate unattended in harsh weather conditions. The application of state-of-the-art electronics increases the quality of backscatter profiles and thus qualifies modern ceilometers for applications beyond...

Mineral dust has a significant impact on air quality by reducing visibility and causing adverse health effects on humans such as increased respiratory symptoms and decreased lung function. Ground-based monitoring of PM10 and PM2.5 is the common metric used for assessing air quality degradation. Because of vast dust sources in Northern China and Mon...

Air pollution episodes in urban areas often occur during low wind speeds and low mixing layer height (MLH) and can not only be ascribed to increased local anthropogenic emissions. The continuous knowledge of MLH is supporting the understanding of processes directing air quality. If the MLH is located near to the ground, which occurs mainly during w...

Daily PM2.5 samples were collected continuously with two high-volume samplers at the ground of CUGB from 06/2010 until 06/2011. The site is very near to the instrumentation for long-term investigation of the inorganic composition of PM2.5 (DWD, KIT/IMG). The daily filter samples are analyzed for carbon fractions, organic compound speciation (HMGU,...

The physical and chemical characteristics of aircraft plumes at the take-off phase are simulated with the mesoscale CAMx model using the individual plume segment approach, in a highly resolved domain, covering the Athens International Airport. Emission indices during take-off measured at the Athens International Airport are incorporated. Model pred...

The goal of this study is to characterize the sensible (H) and latent (LE) heat exchange for different land covers in the heterogeneous steppe landscape of the Xilin River catchment, Inner Mongolia, China. Eddy-covariance flux measurements at 50–100 m above ground were conducted in July 2009 using a weight-shift microlight aircraft. Wavelet decompo...

A comparative study and evaluation of mixing-layer height estimation was conducted, using data from remote sensing and in-situ instrumentation, radiosondes, synoptic analyses and model simulations. The data were collected during an experimental campaign conducted at the Athens International Airport, Greece, from 15 to 26 September 2007. Mixing-laye...

The goal of this study is to characterize the sensible (H) and latent (LE) heat exchange for different land covers in the heterogeneous steppe landscape of the Xilin River Catchment, Inner Mongolia, China. Eddy-covariance flux measurements at 50-100 m above ground were conducted in July 2009 using a weight-shift microlight aircraft. Wavelet decompo...

The mixing layer height (MLH) is an important factor which influences exchange processes of ground level emissions. The continuous knowledge of MLH is supporting the understanding of processes directing air quality. If the MLH is located near to the ground, which occurs mainly during winter and night-time, air pollution can be high due to a strongl...

Ceilometers are applied by KIT/IMK-IFU to detect layering of the lower atmosphere continuously. This is necessary because not only wind speed and direction but also atmospheric layering and especially the mixing layer height (MLH) influence exchange processes of ground level emissions. It will be discussed how the ceilometer monitoring information...

Emissions of the major greenhouse gas NO from soils are characterized by huge spatial variability. An upscaling based on conventional small-scale chamber measurements is thus questionable and may involve a considerable amount of uncertainty. In this feasibility study, we evaluated the applicability of a large, closed tunnel for field-scale measurem...

Measurements of land-surface emission rates of greenhouse and other gases at large spatial scales (10 000 m2) are needed to assess the spatial distribution of emissions. This can be readily done using spatial-integrating micro-meteorological methods like flux-gradient methods which were evaluated for determining land-surface emission rates of trace...

Since 2006 different remote monitoring methods for determining mixing-layer height have been operated in parallel in Augsburg (Germany). One method is based on the operation of eye-safe commercial mini-lidar systems (ceilometers). The optical backscatter intensities recorded with ceilometers provide information about the range-dependent aerosol con...

More than 15 million people in the greater area of Beijing are still suffering from severe air pollution levels caused by sources within the city itself but also from external impacts like severe dust storms and long range advection from the southern and central part of China. Within this context particulate matter (PM) is the major air pollutant...

Measurements of land-surface emission rates of greenhouse and other gases at large spatial scales (10 000 m2) are needed to assess the spatial distribution of emissions. This can be more readily done using spatial-integrating micro-meteorological methods than the widely-utilized small chamber measurements. Several micro-meteorological flux-gradient...

Measuring N2O emissions from soils is challenging as they are notoriously variable in space and time. A vast majority of measurements to quantify N2O emissions are conducted using chamber techniques. Since chambers usually cover a rather small surface area (<1 m2), the method has its limitations, particularly in tackling the spatial variability of...

Direct thermal desorption and in-situ derivatization thermal desorption methods in conjunction with gas chromatography time-of-flight mass spectrometry have been characterized and evaluated for analysis of trace components from filters loaded with ambient particulate matter (PM). The limits of quantification were in the range of 7–24 pg for n-alkan...

The mixing layer height (MLH) is an important factor which influences exchange processes of ground level emissions. The continuous knowledge of MLH is supporting the understanding of processes directing air quality. If the MLH is located near to the ground, which occurs mainly during winter and night-time, air pollution can be high due to a strongl...

An experimental campaign has been conducted in the frame of the European Commission funded network of excellence ECATS, at Athens International Airport (AIA), Greece, from 13 to 25 September 2007. In order to quantify the background air quality and study the influence of meteorological conditions and airport emissions to the broader region, the ana...

Ceilometers are applied to detect layering of the lower atmosphere continuously. This is necessary because not only wind speeds and directions but also atmospheric layering and especially the mixing layer height (MLH) influence exchange processes of ground level emissions. It will be discussed how the ceilometer monitoring information can be used t...

Available CL31 ceilometer measurements (backscatter profiles at 910 nm) have been applied to detect the Eyjafjallajökull volcanic plume after the eruption on April 14th, 2011. Ceilometer backscatter intensities in Augsburg showed a layer of strongly enhanced backscatter above the planetary boundary layer (PBL) only on April 17th until 13:00. From...

Eye-safe lidar ceilometers are reliable tools for unattended boundary layer structure monitoring around the clock. A single lens optical design enables precise assessment of inversion layers and nocturnal stable layers below 200 m. This design has been chosen for the Vaisala Ceilometers CL31 and CL51. Based on the gradient method, an automatic algo...

The spatial structure and the progression speed of the first ash layer from the Icelandic Eyjafjallajokull volcano which reached Germany on 16/17 April is investigated from remote sensing data and numerical simulations. The ceilometer network of the German Meteorological Service was able to follow the progression of the ash layer over the whole of...

A series of major eruptions of the Eyjafjallajökull volcano in Iceland started on 14 April 2010 and continued until the end of May 2010. The volcanic emissions moved over nearly the whole of Europe and were observed first on 16 April 2010 in Southern Germany with different remote sensing systems from the ground and space. Enhanced PM10 and SO2 conc...