Jost Heintzenberg

Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze

Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one- and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (±10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20±4 W m^(−2)) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate.

Design and Calibration of a Counterflow Virtual Impactor for Sampling of Atmospheric Fog and Cloud Droplets

An instrument is described that samples cloud droplets by removing them from the surrounding air and small unactivated particles through inertial impaction. The sampled droplets are then evaporated, leaving behind the material dissolved or suspended in the droplets as residue particles or gases. The instrument is capable of sampling droplets as a function of their size; it has an adjustable cut size in the range between about 9 and 30 μm in diameter, rejects droplets and particles smaller than the cut size, and captures droplets larger than the cut size. Details of the instrumental design and construction are discussed, as well as a relative calibration of the collection efficiency. Results from the calibration experiments indicate that the counterflow virtual impactor probe behaves in accordance with theoretical predictions using Stokes number calculations. A complete description of the calibration methodology is presented.

Atmospheric particle number size distribution in central Europe: Statistical relations to air masses and meteorology

Atmospheric particle number size distributions determined over 1.5 years at a central European site were statistically analyzed in terms of their relation to time of day, season, meteorology, and synoptic-scale air masses. All size distributions were decomposed into lognormal particle modes corresponding to the accumulation, Aitken, aged nucleation, and nucleation modes. The concentration of nucleation mode particles ( 30 nm) lacked such diurnal behavior, and proved to be indicative of different synoptic-scale air mass types. Over 70% of the time, air masses of Atlantic origin and maritime character prevailed, showing obvious signs of anthropogenic influence most of the time (accumulation mode: 500 cm−3; Aitken mode: 2300 cm−3). During a limited period of time (10%), however, continentally aged air with significantly enhanced concentrations of aerosol was observed (accumulation mode: 1200 cm−3; Aitken mode: 3300 cm−3). These air masses were advected from source regions in Russia, and eastern, southeastern, and central Europe, mainly under anticyclonic and high-pressure influence. The analysis provides a refined picture of the behavior of the particle number size distribution and provides parameterizations that are representative for a variety of air masses in Europe and thus suitable for future climate modeling applications.

Size-segregated measurements of particulate elemental carbon and aerosol light absorption at remote arctic locations

Abstract Size-segregated aerosol samples were taken during 2 winter pollution periods and in clean summer air at different remote locations in the European Arctic > 74°N. By means of a newly developed integrating sphere photometer these filter samples have been analysed for aerosol light absorption coefficients and particulate elemental carbon (PEC). The relatively high PEC concentrations in winter confirm other findings about the Arctic winter atmosphere having an aged continental aerosol burden. In summer very low light absorption coefficients of 4.5 × 10−8 m−1 were measured, similar to upper tropospheric background values. For the climatically important months of March-May the key optical aerosol properties (extinction coefficient, single scattering albedo and absorption to backscatter ratio) were determined. Based on the approach of J.M. Mitchell (1971, in Mans Impact on Climate. MIT Press, Cambridge, MA) the Arctic haze aerosol is found to contribute to atmospheric heating, even in the summer. A first PEC size distribution was determined in a clean polar summer air. The results show systematic variations in the PEC size distribution from urban to remote locations and seasonal variations in the sink region which may be exploited to quantify aerosol removal process in long distance transport studies.

The SAMUM‐1 experiment over Southern Morocco: overview and introduction

In May/June 2006, the largest mineral dust experiment to date (Saharan Mineral Dust Experiment, SAMUM-1) was conducted in Southern Morocco. The aim was to characterize dust particles near the world’s largest mineral dust source, and to quantify dust-related radiative effects. At one of the two ground-based measurement sites dust particle size distribution, optical, hygroscopic, chemical and structural particle characteristics were measured. One research aircraft mainly measured solar spectral irradiances and surface albedo. The other aircraft provided in situ physical aerosol measurements and samples and lidar profiles through the dust layers. Three ground-based lidars were operated at the second ground-based measurement site. They determined optical dust properties, particle shape and temporal development of dust layers. Columnar, ground-based sun photometer measurements complemented the lidar data. Additionally a station in Èvora, Portugal monitored dust outbreaks from the North African source region to the Iberian Peninsula during SAMUM-1. Volumetric and columnar closure exercises utilized these detailed measurements of dust characteristics together with optical and radiative transfer models. Concurrent developments of a mesoscale dust transport model were validated with the experimental data. The paper gives an overview over rationale and design of SAMUM-1, introduces and highlights the subsequent reports on experimental and modelling results.

Saharan Mineral Dust Experiments SAMUM-1 and SAMUM-2: What have we learned?

Two comprehensive field campaigns were conducted in 2006 and 2008 in the framework of the Saharan Mineral Dust Experiment (SAMUM) project. The relationship between chemical composition, shape morphology, size distribution and optical effects of the dust particles was investigated. The impact of Saharan dust on radiative transfer and the feedback of radiative effects upon dust emission and aerosol transport were studied. Field observations (ground-based, airborne and remote sensing) and modelling results were compared within a variety of dust closure experiments with a strong focus on vertical profiling. For the first time, multiwavelength Raman/polarization lidars and an airborne high spectral resolution lidar were involved in major dust field campaigns and provided profiles of the volume extinction coefficient of the particles at ambient conditions (for the full dust size distribution), of particle-shape-sensitive optical properties at several wavelengths, and a clear separation of dust and smoke profiles allowing for an estimation of the single-scattering albedo of the biomass-burning aerosol. SAMUM–1 took place in southern Morocco close to the Saharan desert in the summer of 2006, whereas SAMUM–2 was conducted in Cape Verde in the outflow region of desert dust and biomass-burning smoke from western Africa in the winter of 2008. This paper gives an overview of the SAMUM concept, strategy and goals, provides snapshots (highlights) of SAMUM–2 observations and modelling efforts, summarizes main findings of SAMUM–1 and SAMUM–2 and finally presents a list of remaining problems and unsolved questions.

Sulfate Cooling Effect on Climate Through In-Cloud Oxidation of Anthropogenic SO2

Anthropogenic SO2 emissions may exert a significant cooling effect on climate in the Northern Hemisphere through backscattering of solar radiation by sulfate particles. Earlier estimates of the sulfate climate forcing were based on a limited number of sulfate-scattering correlation measurements from which a high sulfate-scattering efficiency was derived. Model results suggest that cloud processing of air is the underlying mechanism. Aqueous phase oxidation of SO2 into sulfate and the subsequent release of the dry aerosol by cloud evaporation render sulfate a much more efficient scatterer than through gas-phase SO2 oxidation.

Design and Applications of the Integrating Nephelometer: A Review

Abstract The purpose of this paper is to document the key literature references and to describe the design philosophy. the principles of the instrument, the various possible designs, calibration, systematic errors, applications to scientific problems and inherent limitations. According to the design philosophy established in the original publication, instruments are devised to directly measure the relevant integral aerosol parameters, thus eliminating the need for assumptions about particle size distribution, particle shape and composition, complex Mie calculations, and the unknown uncertainties associated with them. The key parameter measured by the integrating nephelometer is the scattering component of extinction as a function of wavelength. This philosophy subsequently allows two approaches to the determination of several parameters—direct measurement with the aid of the integrating nephelemeter and calculation via the Mie formalism. Comparison of calculated and measured values for a parameter allows ...

Information content of optical data with respect to aerosol properties: numerical studies with a randomized minimization-search-technique inversion algorithm.

The information content of a set of optical data with respect to the particle size distribution is discussed in a numerical study. We show how the kernels of the integral equation relating size distribution and optical properties can be used to determine the particle size range in which an inversion of the size distribution is possible. We present an iterative least squares fit algorithm allowing the inversion of optical data to yield a histogram distribution for the particle size distribution. We discuss the uniqueness and stability of the solutions in relation to the range of radii and in relation to the number of histogram columns by means of synthetic data calculated via Mie theory.

Shape of atmospheric mineral particles collected in three Chinese arid‐regions

The shape of atmospheric mineral particles of 0.1–6 µm radius was studied by electron microscopy applied to the samples collected in three arid regions in China (Qira in the Taklamakan Desert, Zhangye near the southern border of the Badain-Jaran Desert and Hohhot in northern China). In all three regions, the mineral particles showed irregular shapes with a median aspect ratio b/a (ratio of the longest dimension b to the orthogonal width a) of 1.4. Although the aspect ratio exhibited no clear size dependence, the circularity factor (4πS/l²; S is surface area and l is periphery length) tended to decrease with increasing radius, suggesting the presence of aggregated mineral particles at larger sizes. The ratio of particle height-to-width h/a was also evaluated by measuring the shadow length. The median ratio h/a was 0.49 in Hohhot, 0.29 in Zhangye and 0.23 in Qira. Analytical functions were fitted to the grand total of the frequency distributions of aspect ratios, height-to-width ratios and circularity factors allowing parametric calculations of radiative effects and calculations of optical and sedimentation behavior of mineral particles.