## 11 Development Trends and Summary  
Odour nuisance has become an increasingly critical issue in environmental protection, especially in the context of expanding urbanisation, industrial intensification and growing public awareness of air quality. Despite significant advances in monitoring technologies and a general improvement in environmental legislation, the management of odour emissions remains a major challenge due to the complex nature of odorous compounds, their variability in time and space and the subjective perception of odours by humans. Current research trends point to three main directions that are pivotal to improving odour nuisance assessment and control: the development of advanced measurement technologies, the harmonisation of legal frameworks, and the implementation of sophisticated data analysis and modelling methods. Measurement techniques for odour assessment are traditionally classified into subjective and instrumental methods. Dynamic olfactory, standardised under EN 13725, remains the primary reference method in Europe. It relies on human panellists to determine odour concentration, providing results that reflect actual human perception. However, its limitations, including high costs, dependence on individual variability, and the inability to conduct continuous monitoring, have driven the search for alternative approaches. Among these, electronic noses (e-noses) have gained attention; these devices combine arrays of gas sensors with pattern recognition algorithms to detect changes in air quality. Despite technological progress, their application is still limited by calibration challenges, environmental variability and the complexity of ambient odour mixtures. More advanced instrumental techniques such as selected ion flow tube mass spectrometry (SIFT-MS) and proton transfer reaction mass spectrometry (PTR-MS) allow the real-time, sensitive detection of volatile organic compounds (VOCs) responsible for odours. Additionally, Fourier-transform in -frared spectroscopy (FTIR) offers the capability to analyse multi-component gas mixtures continuously, making it a valuable complement to traditional methods. From a regulatory perspective, significant disparities exist globally. Within the European Union, no overarching directive governs odour emissions, leading to heterogeneous national approaches. Germany's GIRL guidelines and the Netherlands' odour unit standards represent advanced regulatory models that establish quantitative emission limits and odour impact criteria. In contrast, many countries, including Poland, lack specific regulations, complicating odour management. In the United States, ASTM E679-19 provides a technical standard for determining odour detection thresholds, while individual states such as Colorado and Minnesota have adopted specific regulatory frameworks addressing agricultural and industrial odour sources. Australia has developed rigorous requirements for dispersion modelling and health risk assessment of odour emissions. Meanwhile, Asian countries like Japan and South Korea have introduced sector-specific odour emission standards. Efforts at the European level, particularly within the framework of the Zero Pollution Action Plan, aim to establish harmonised odour management standards by 2030, which would represent a significant advancement in ensuring equal protection against odour nuisance across member states. Advances in statistical data analysis have played a pivotal role in modern odour research. Beyond basic descriptive statistics and exceedance frequency analysis, sophisticated techniques such as multiple regression models, logistic regression, and time series forecasting (e.g., ARIMA and SARIMA models) are increasingly used to analyse the relationship between meteorological variables and perceived odour intensity. Dispersion modelling using systems like AERMOD, CALPUFF and WRF-Chem enables the simulation of the transport and spread of odours in the atmosphere, considering meteorological variability, topography and source emission characteristics.