Herbert Hoffmann

Influence of mixing layer height upon air pollution in urban and sub-urban areas

The mixing layer height is an important parameter characterising the potential of the atmospheric boundary layer to take up emitted air pollutants. During continuous measurements in Hanover, Germany, from 2001 until 2003 and around Munich, Germany, in summer and winter 2003 mixing layer heights (MLH) were determined by different remote sensing systems mainly from the thermal structure and turbulence of the air (SODAR), for some time from the aerosol layering of the air (ceilometer), and for a short period directly from the temperature profile (RASS). The temporal variations of the concentrations of PM 10 and PM 2.5 as well as of CO and NO x simultaneously measured near the surface were investigated and correlated with the MLH derived from SODAR data. The pollution measurements were performed inside a street canyon and at an urban background station close to Hanover and at three measurement locations inside and outside of Munich complementing the available monitoring networks. The analyses show that the correlations of pollutant concentrations with MLH are smallest inside street canyons. Correlations at the urban background stations are larger in winter than in summer, and they are larger for the urban stations than for the rural stations. It turns out further that the correlation of NO X concentrations with MLH is larger than the correlation of particles concentrations. Explanations for these findings must consider the varying emission source strengths for NO X and particles and the influence of gas-to-particle conversion within air masses especially during daytime in summer.

Field measurements within a quarter of a city including a street canyon to produce a validation data set

Air pollutants and meteorological parameters were measured continuously by in situ instruments, path-averaging techniques (up to three DOAS systems), and SODAR inside a street canyon and in the surrounding area of 1 km x 1 km (Gottinger Strasse in Hanover, Germany) from 2001 until 2003 which are available in the data bank ValiData for validation of microscale models. During three IOPs tracer experiments with a SF6 line source, sampling techniques of up to 15 sites and path-averaging FTIR spectrometry were performed. Concentration measurement results at roof level were anti-correlated with SODAR mixing layer heights, while those inside the street canyon are not. Re-circulation flow patterns inside the street canyon were studied together with corresponding wind tunnel experiments.

Fusion of air pollution data in the region of Munich, Germany, by the ICAROS NET platform

The air quality in Munich is monitored by the measurement network of the Bavarian Agency for Environmental Protection. Additional information can be provided from retrievals of optical thickness and corresponding particle concentrations from satellite images in an area of approximately 100 km x 100 km (depending on the satellite sensor used). The satellite measures the optical thickness of the entire atmosphere, which has to be attributed mainly to the mixing layer. The mixing layer height is determined either by remote sensing, by radiosondes, or by numerical models of the boundary layer. The corrected optical thickness of the satellite images can be interpreted as the particle concentration in the mixing layer. Data from the ground-based monitoring network and from satellite retrievals are fused in the ICAROS NET platform. This platform is applied to supply additional information on the air quality in the Munich region and it is tested as well as evaluated during field campaigns in summer and winter. The adaptation to the Munich region covers the development of routines for the collection of data, for example from the measuring network, and the disposal of information, which were defined by the Bavarian agency for environmental protection. During measurement campaigns in and around Munich PM 10, PM 2.5 and PM 1.0 concentrations and mixing layer heights by remote sensing (SODAR, ceilometer, WTR) were determined. Temporal variations of the concentration, the spatial distribution (3 measurement locations) and concentration conditions for selected particle sizes are presented.

Airport air quality and emission studies by remote sensing and inverse dispersion modelling

Airport air quality is influenced by traffic mainly. These are emissions from road traffic and aircraft. A measurement campaign on the airport Budapest was performed to investigate airport air quality and to identify major sources of air pollutants and to assess air quality for this airport. At four different locations, concentration of CO, CO2, NO, NO2 and PM10 as well as meteorological parameters were measured simultaneously. Measurement methodologies were classical in-situ techniques and open-path techniques (DOAS and FTIR). Highest concentrations were found during low wind speed conditions downwind of the airport. To quantify emissions on the airport, inverse dispersion modelling with a Bayesian approach was used on the basis of hourly averaged concentration measurements. Single emissions rates were highest for a car park, while for the whole campaign, aircraft emissions on the taxiway around terminal 2 are most important. Similar levels of emissions are reached for the car park and the freight area. Even though the most important source for NOx on an airport, starting aircrafts, were not considered during this investigation, the results reveal, that dealing with air quality on airports, all sources of NOx are important, and not only aircrafts.

Emission rates of benzene and ammonia area sources determined by spectroscopic remote measurements and inverse dispersion modeling

The emission rates of diffuse and heterogeneous distributed sources are difficult to determine because point measurements are not representative. Therefore a method was further developed to determine gaseous emission rates by measurements of path-integrated mixing ratios with open-path spectroscopic systems in the exhaust plume (VOC, NH3, CH4, N2O, CO, CO2) and of meteorological parameters. Inverse dispersion modeling is used to quantify the emission rates afterwards with these data. The measurements are performed by Fourier Transform Infrared (FTIR) spectroscopy and Differential Optical Absorption Spectroscopy (DOAS) at 50 to 500 m optical path lengths about 1 to 20 m above ground level. The measurement accuracy for greenhouse gases and ammonia is about plus or minus 10% and for BTX about plus or minus 30%. The whole method was validated at a livestock building with a single exhaust chimney. The Gaussian model PAL was applied for inverse modeling to investigate limited pieces of land and isolated facilities in flat terrain. Including the accuracy of the dispersion simulations the determined emission rates have an error margin of about plus or minus 30%. Results of measurement campaigns are discussed as emission rates of ammonia from slurry spreading as well as of benzene from gas stations and a tank farm.

Budapest airport air quality long-term studies by remote sensing with DOAS and FTIR with focus upon runway emissions

Airport air quality is influenced by traffic mainly. Near runway the aircrafts are the main source. The quantification of these emission sources requires remote sensing methods because the airport operations should not be disturbed. DOAS is used in open-path mode to detect continuously NO2 cross the runway during nearly one year. Those runway emission studies were performed for the first time. During the measurement campaign these findings were compared with corresponding aircraft taxiway emission measurements. The concentration measurements of CO2 which are necessary to calculate emission indices are provided by open-path FTIR spectrometry. Aircraft emission indices of CO, NO and NO2 could be determined at taxiway only. Open questions and required further developments will be discussed.

Highway emission study by DOAS within the Inn valley near Innsbruck

To study the development of high air pollution episodes in a valley with urban areas, industry and transit traffic a highway emission study was performed in the Inn valley near Innsbruck, Austria. A DOAS consisting of a emitter/receiver unit and three retroreflectors was used for this study. One path was across the highway (120 m path length) in about 10 m altitude above highway level. Another path was set up in parallel to the highway and the third path was operated perpendicular to and away from the highway. The path across the highway was directly above the air pollution monitoring station Vomp which is only three meters away from the motorway. A measurement campaign was performed between October 2005 and February 2006 including an inter-comparison of the DOAS with in situ measurement devices for NO and NO2 during one week at a site (near Schwaz) in some distance to the main emission sources. The concentrations of NO and NO2 above the highway are clearly dominated by the traffic volume. Higher concentration values were found during week days than during the weekend. The concentrations above the highway are compared to those measured at the other DOAS paths. The daily differences in air pollution e.g. due to temporal variations of highway emissions (10 times higher during peak hours in the morning and afternoon compared to night hours) and meteorological conditions (wind directions) are investigated.

Detection of emission indices of aircraft exhaust compounds by open-path optical methods at airports

Air pollutant emission rates of aircrafts are determined with test bed measurements. Regulations exist for CO2, NO, NO2, CO concentrations, the content of total unburned hydrocarbons and the smoke number, a measure of soot. These emission indices are listed for each engine in a data base of the International Civil Aviation Organisation (ICAO) for four different Air pollutant emission rates of aircrafts are determined with test bed measurements. Regulations exist for CO2, NO, NO2, CO concentrations, the content of total unburned hydrocarbons and the smoke number, a measure of soot. These emission indices are listed for each engine in a data base of the International Civil Aviation Organisation (ICAO) for four different thrust levels (Idle, approach, cruise and take-off). It is a common procedure to use this data base as a starting point to estimate aircraft emissions at airports and further on to calculate the contribution of airports on local air quality. The comparison of these indices to real in use measurements therefore is a vital task to test the quality of air quality models at airports. Here a method to determine emission indices is used, where concentration measurements of CO2 together with other pollutants in the aircraft plume are needed. During intensive measurement campaigns at Zurich (ZRH) and Paris Charles De Gaulle (CDG) airports, concentrations of CO2, NO, NO2 and CO were measured. The measurement techniques were Fourier-Transform-Infrared (FTIR) spectrometry and Differential Optical Absorption Spectroscopy (DOAS). The big advantage of these methods is that no operations on the airport are influenced during measurement times. Together with detailed observations of taxiway movements, a comparison of emission indices with real in use emissions is possible.

VOC emission source strengths of tankers during refuelling activities determined by spectroscopic remote sensing and inverse dispersion modeling

Tankers are a wide spread and important emission source of VOCs. Up to now emission data are available from measurements inside the storage tanks to investigate explosion protection only. Different emission reduction systems are under discussion such as vapor recovery units. The environmental impact of these alternatives shall be investigated. The VOC emissions of tankers were investigated in a river harbor. Fence-line monitoring by Differential Optical Absorption Spectroscopy (DOAS) was performed to investigate different emission sources during activities of tankers in harbors. Benzene, toluene and p-xylene concentrations were measured by a mono-static DOAS using 3 retro-reflectors. The inverse method was applied on the basis of these non-intrusive measurements of effluent concentrations in the exhaust plume and meteorological measurements to determine the emission source strengths. Inversion of effluents dispersion was performed by a Lagrangian model driven by wind fields of the Eulerian model MISKAM considering influences from buildings and the orography upon the streaming fields. The emission source strengths were determined from unloading and loading of gasoline, from ventilation of storage tanks of tankers into ambient air which is of common practice if the tankers are operated without load or if the tankers are to be refueled with a different product than before and from using the land-site gasoline vapor recovery unit in a tank farm for ventilation.

Emission source strengths of gasoline-filling processes determined by open-path spectroscopic techniques and inverse modeling

Up to now emission source strengths of diffuse and heterogenous emission of important VOCs are not well known especially from gas stations and gasoline tank farms. To estimate the total emission of these sources non-intrusive measurements were performed by a differential optical absorption spectroscopy (DOAS) system to determine the path- integrated concentrations of exhaust compounds downwind of the source through the whole exhaust plume. Simultaneously, the meteorological parameters were measured for modeling the dispersion of the plume inversely to obtain the emission source strengths of these compounds. The emissions by road traffic were determined by an additional open-path DOAS measurement. Measurement campaigns were performed during different wether conditions and at different sources which were characterized by well defined and easy air flow conditions. The emission source strengths were calculated with the Gaussian model PAL. The determined total emission of gas stations with gasoline vapor recovery system are about 20 mg benzene per kg refueled gasoline and the emission from refueling activities vary between 1 and 9 benzene per kg refueled gasoline depending on the technical behavior of the gasoline vapor recovery system. These values which were found from measurements during times with a and without refueling activities show a high amount of diffuse emissions. The emission rates from a gasoline taken farm were measured on an open path through the middle of that area and a maximum of 8 (mu) g/(m2s) was determined.