Vol. 117, No. 4 * Pages 359–450 * October - December 2013

The harmful effect of air pollution on human health have raised a series of concerns in recent years and imposed needs for accurate descriptions of air pollution levels in urban areas. This implies that tools supporting national pollution control and planning need to be developed including public web sites or other media, where citizens exposed to the air pollutants can catch urban background concentration data, predicted concentrations, or alerts. In recent years, PM₁₀ episodes caused the most critical air quality problems in Budapest. Before the development of air quality forecasting systems, which help to predict the high PM₁₀ concentration episodes, the main determinants have to be identified. In this work, the effect of long-range transport and meteorological conditions on PM₁₀ concentration in Budapest was analyzed in detail, as well as the results of an existing air quality forecasting systems were evaluated in case of PM₁₀.

Absorption and transfer of radiation in clouds are sensitive to size distribution of water drops. A new numerical scheme has been developed for calculating the extinction coefficients of water clouds in the longwave region. While the generally applied bulk schemes in numerical models characterize the whole size distribution of the water droplets with one parameter (effective radius), detailed models allow us to calculate the optical properties without any assumption about the size distribution of water drops. Our model uses a bin microphysical scheme which uses the number concentration and mixing ratios of water in 36 size intervals.
This paper describes the developed bin radiation scheme. The wavelength-dependence of extinction coefficients calculated by bin and bulk schemes is compared at different effective radius. It was also investigated how the number concentration of droplets and liquid water content affect the difference between the two schemes. The relative difference depends both on the effective radius and on the wavelength. If the effective radius is larger than 10 µm, the relative difference remains below 20%. It is higher in the case of smaller effective radius.
The bin scheme has also been implemented in the RRTM LW radiation transfer model code. Upward, downward, and net radiation profiles for four different cases were studied with the RRTM model. It was found that the outgoing longwave radiation is sensitive on the applied scheme when the cloud layer is thin. Significant differences were found between the gradients of the net longwave radiation profiles in all cases. These differences have significant impact on the evolution of the vertical temperature profiles, which affects both cloud dynamics and microphysics.

Aims of the spectral radiation measurements can be devided to two wider areas: one is to get information about the radiation source, and the other is to get information about the properties of the space between the radiation source and the detector if output signal from the radiation source is known. In the latter case either the optical properties of the certain space or some optical parameter of an object placed in there is to be studied. The sun can be the object of the study or it can be used as natural radiation source to investigate some important properties of the atmosphere. The term ’solar spectrophotometry’ refers to this.
Although detection of spectral distribution of the solar radiation is considered a special area that is relatively rarely used even today in atmospheric physical measurements, it still has big significance. In addition to the ’mere’ knowledge of spectal solar irradiance, the measured data can be used in a considerably wide range. In special cases, the narrow spectral range informations about the radiation can be very useful. Typical example is the erythemally weighted UV radiation. Though it does not give spectral information, the spectral range that is characterized by it, is considerably narrower than that of the classical radiation components. So this type of measurements is also discussed here.
Main applied physical and technical principles of solar spectrophotometry, as well as spectrophotometers working in the UV, visible, and near infrared spectral range used at the Hungarian Meteorological Service (HMS), are shown in this paper. Measurement results and results from studies and researches using these data are also shown and analyzed. Also some special studies performed occasionally are shown.
Today the primary base for operation of high accuracy measurement systems is the calibration. Since we have reference instruments, QA/QC procedures are of crucial importance in our measuring practice. Our activitiy as we operate WMO Regional Center for Solar Radiation in Region VI gives even bigger emphasis to that.

Industrial accidents have been a serious environmental and public health issue for the last decades. Although the development of atmospheric dispersion models was largely motivated by the notorious nuclear catastrophes, simulations are now mostly used in cases of chemical accidents that regularly occur in all parts of the world. In an accidental situation, the accuracy of the results is primarily important for risk management and decision making strategies. However, it largely depends on the meteorological conditions and the quality of input data. A chemical accident happened in a factory in Rouen, France on January 21, 2013. The emitted methyl mercaptan gas caused odor and sickness in densely populated areas, including Paris. The meteorological conditions were rapidly changing in both space and time during the release period, thus the case is particularly challenging for dispersion models and provides a good basis for testing them.
Dispersion of the released methyl mercaptan gas was estimated using the PyTREX trajectory model, developed at the Eötvös Loránd University, and NOAA’s HYSPLIT model. The simulation results are in a good agreement with media reports of the polluted areas, and lead to a better understanding of the complex synoptic situation at the time of the accident. Comparison of the results of two models also provided information about the uncertainty of the predictions and pointed out the most important directions for further development of the PyTREX model.