Showing papers by "Ulrich Platt published in 2008"

Air Pollution Monitoring Systems—Past–Present–Future

Abstract: Measurements of trace gas concentrations and other parameters like photolysis frequencies are a crucial tool for air pollution monitoring and the investigation of processes in the atmosphere. However, the determination of atmospheric trace gas concentrations constitutes a technological challenge, since extreme sensitivity (mixing ratios as low as 10) is desired simultaneously with high specifi city i.e. the molecule of interest usually must be detected in the presence of a large excess of other species. In addition, spatially resolved measurements are becoming increasingly important. Today none of the existing measurement techniques meets all above requirements for trace gas measurements in the atmosphere. Therefore, a comprehensive arsenal of different techniques has been developed. Besides a large number of special techniques (like the ubiquitous short-path UV absorption for O 3 measurement) universal methods gain interest, due to their economy and relative ease of use. In particular, a single instrument can register a large number of different trace species. The different types of requirements and the various techniques are discussed; special emphasis is given to spectroscopic methods, which play a large and growing role in atmospheric chemistry research. For instance, only spectroscopic methods allow remote sensing and spatially resolved determination of trace gas concentrations e.g. from space-borne platforms. Today many varieties of spectroscopic methods are in use (e.g. tunable diode laserand Fourier-transform spectroscopy). The basic properties and recent applications of this technique are presented using differential optical absorption spectroscopy (DOAS) as an example. Future requirements and expected developments are discussed.

Biomass burning emissions from satellite observations: synergistic use of formaldehyde (HCHO), fire counts, and surface temperature

Abstract: Satellite observations provide unique opportunities for the identification of trace gas sources on a global scale. We present case studies for the synergistic use of satellite observations by comparing formaldehyde (HCHO) time series with fire count measurements as well as with surface temperature to identify the tropospheric sources of HCHO. The fire counts and temperature are taken as proxy for biomass burning events and vegetation activity, respectively. Both are sources of HCHO, either direct or trough photochemical oxidation of non-methane hydrocarbons (e.g. biogenic isoprene emissions). Formaldehyde time series are derived from satellite observations made by the GOME instrument. This instrument provides almost 8 years of continuous HCHO global observations, which constitute an ideal case to calculate time series over specific regions for various trace gases. Nine regions have been selected to investigate the influence of fire counts (biomass burning proxy) and the temperature (vegetation activity proxy) on the HCHO tropospheric columns. The chosen time series has a length of 6 years (from July 1996 to June 2002). The results show that biogenic sources of HCHO are in many cases the strongest HCHO sources. For example over south east of the USA, the correlation with temperature was very high indicating a strong biogenic source of HCHO (through isoprene emissions). The biomass burning source typically shows more pronounced seasonal patterns or is even of sporadic nature. Over the Amazon region, the correlation with fires is high indicating that in this area most of the HCHO is caused by biomass burning. In several other regions for both sources moderate correlation coefficients were found.

Differential Optical Absorption Spectroscopy (DOAS) using Targets: SO2 and NO2 Measurements in Montevideo City

Abstract: SO2 and NO2 were remotely measured in a main street of Montevideo city using Multiaxis‐Differential Optical Absorption Spectroscopy (MAX‐DOAS) combined with on‐field selected targets. Target‐based measurements are the basis of a new experimental procedure called Topographic Target Light scattering‐DOAS (TOTAL‐DOAS) that provides a well define absorption path to measure the near surface distribution of trace gases in the boundary layer. It combines the measurement principles of the long‐path DOAS and zenith‐scattered sunlight DOAS, within the near UV and VIS spectral range. We give a general description of the procedure and present first results of the 2006 campaign at Montevideo.