Odor impact criteria around the world: is protection from odor nuisance consistent across the globe?

Odorous emissions from agricultural and industrial activities are a major source of pollution. As urban areas expand, odor sources often lie closer to sensitive receptors, intensifying conflicts and attracting growing attention from researchers and regulators. In Europe, odor has recently been acknowledged as an atmospheric pollutant in the revised Industrial Emissions Directive (IED 2.0). However, the absence of harmonized Odor Impact Criteria (OICs) across jurisdictions results in highly variable approaches to odor impact assessment. This study analyzes the implications of such regulatory heterogeneity through a comparative evaluation of existing OICs and their application using the CALPUFF dispersion model. Results show that different OIC definitions—combining concentration thresholds, percentiles, and averaging times—lead to substantial variation in predicted impacts. Non-European countries generally exhibit higher exceedance percentages and broader isopleths, whereas European regulations tend to yield lower exceedance levels more localized around sources. Nevertheless, considerable variability is also found within Europe, even between regions of the same country, with Italy standing out for applying the strictest criteria in Europe. Population density emerges as a statistically significant driver of regulatory stringency, reflecting attempts to balance environmental health protection with industrial and economic development. While stricter OICs strengthen safeguards for exposed populations, they may also impose higher compliance costs, whereas more lenient criteria risk undermining citizens’ well-being and property values. The findings highlight the risks of adopting OICs without critical evaluation and underscore the need for harmonized standards—particularly within the EU—to ensure consistent environmental protection.