Advancing exposure data analytics and repositories as part of the European Exposure Science Strategy 2020-2030.

High-quality and comprehensive exposure-related data are critical for different decision contexts, including environmental and human health monitoring, and chemicals risk assessment and management. However, exposure-related data are currently scattered, frequently of unclear quality and structure, not readily accessible, and stored in various-partly overlapping-data repositories, leading to inefficient and ineffective data usage in Europe and globally. We propose strategic guidance for an integrated European exposure data production and management framework for use in science and policy, building on current and future data analysis and digitalization trends. We map the existing exposure data landscape to requirements for data analytics and repositories across European policies and regulations. We further identify needs and ways forward for improving data generation, sharing, and usage, and translate identified needs into an operational action plan for European and global advancement of exposure data for policies and regulations. Identified key areas of action are to develop consistent exposure data standards and terminology for data production and reporting, increase data transparency and availability, enhance data storage and related infrastructure, boost automation in data management, increase data integration, and advance tools for innovative data analysis. Improving and streamlining exposure data generation and uptake into science and policy is crucial for the European Chemicals Strategy for Sustainability and European Digital Strategy, in line with EU Data policies on data management and interoperability.

The European exposure science strategy 2020-2030.

Exposure science is an emerging and rapidly growing field dedicated to all aspects concerning the contact between chemical, biological, physical or psycho-social stressors and human and ecological receptors. With that, exposure science plays a central role in protecting human and ecosystem health, and contributes to the global transition towards a green and sustainable society. In Europe, however, exposure science is currently not sufficiently recognised as a scientific field, resulting in inefficient uptake into policies. In response, the wider European exposure science community developed elements and actions under the auspices of the Europe Regional Chapter of the International Society of Exposure Science (ISES Europe), for identified priority areas, namely education, exposure models, exposure data, human biomonitoring, and policy uptake. In the present document, we synthesize these strategic elements into an overarching 'European Exposure Science Strategy 2020-2030', following three strategic objectives that focus on acknowledging exposure science as an independent and interconnected field, harmonizing approaches and tools across regulations, and exploring collaboration, education and funding mechanisms. To operationalise this strategy, we present concrete key actions and propose initiatives and funding options for advancing the underlying science, cultivating broader education and cross-sector exposure knowledge transfer, and fostering effective uptake of exposure information into policy. We aim at anchoring European efforts in the global exposure science context, with a special focus on the interface between scientific advancements, application in decision support, and dissemination and training. This will help to develop exposure science as a strong scientific field with the ultimate goal to successfully assess and manage various stressors across sectors and geographic scales.

Enhancing the use of exposure science across EU chemical policies as part of the European Exposure Science Strategy 2020-2030.

BACKGROUND: A scientific framework on exposure science will boost the multiuse of exposure knowledge across EU chemicals-related policies and improve risk assessment, risk management and communication across EU safety, security and sustainability domains. OBJECTIVE: To stimulate public and private actors to align and strengthen the cross-policy adoption of exposure assessment data, methods and tools across EU legislation. METHODS: By mapping and analysing the EU regulatory landscape making use of exposure information, policy and research challenges and key areas of action are identified and translated into opportunities enhancing policy and scientific efficiency. RESULTS: Identified key areas of actions are to develop a common scientific exposure assessment framework, supported by baseline acceptance criteria and a shared knowledge base enhancing exchangeability and acceptability of exposure knowledge within and across EU chemicals-related policies. Furthermore, such framework will improve communication and management across EU chemical safety, security and sustainability policies comprising sourcing, manufacturing and global trade of goods and waste management. In support of building such a common framework and its effective use in policy and industry, exposure science innovation needs to be better embedded along the whole policymaking cycle, and be integrated into companies' safety and sustainability management systems. This will help to systemically improve regulatory risk management practices. SIGNIFICANCE: This paper constitutes an important step towards the implementation of the EU Green Deal and its underlying policy strategies, such as the Chemicals Strategy for Sustainability.

Assessment of the opportunities for increasing the availability of EU data on consumer product-related injuries.

The availability of data on consumer products-related accidents and injuries is of interest to a wide range of stakeholders, such as consumer product safety and injury prevention policymakers, market surveillance authorities, consumer organisations, standardisation organisations, manufacturers and the public. While the amount of information available and potentially of use for product safety is considerable in some European Union (EU) countries, its usability at EU level is difficult due to high fragmentation of the data sources, the diversity of data collection methods and increasing data protection concerns. To satisfy the policy need for more timely information on consumer product-related incidents, apart from injury data that have been historically collected by the public health sector, a number of 'alternative' data sources were assessed as potential sources of interest. This study explores the opportunities for enhancing the availability of data of consumer product-related injuries, arising from selected existing and 'alternative' data sources, widely present in Europe, such as firefighters' and poison centres' records, mortality statistics, consumer complaints, insurance companies' registers, manufacturers' incident registers and online news sources. These data sources, coupled with the use of IT technologies, such as interlinking by remote data access, could fill in the existing information gap. Strengths and weaknesses of selected data sources, with a view to support a common data platform, are evaluated and presented. Conducting the study relied on the literature review, extensive use of the surveys, interviews, workshops with experts and online data-mining pilot study.

Indoor air monitoring: Sharing and accessing data via the Information Platform for chemical monitoring (IPCHEM).

BACKGROUND: The European Commission has developed and put in place the Information Platform for Chemical Monitoring Data (IPCHEM), to promote a more coherent approach to the generation, collection, storage and use of chemical monitoring data in relation to humans and the environment. OBJECTIVES: This paper describes the specific development of the IPCHEM thematic module "Products and Indoor Air Data" which aims to facilitate the retrieval of and access to existing and future chemical monitoring data sources stemming from e.g. national monitoring programs of EU Member States and EU funded projects. The current development focusses on harmonised data and metadata templates and code lists related to indoor air monitoring data. METHODS: The extension and revision of the IPCHEM metadata and data collection templates for indoor air monitoring data was based on harmonisation and standardisation efforts on the development of indoor air monitoring protocols and guidelines for monitoring indoor pollution attributed to chemical and biological stressors, which were undertaken by European Commission Services, EU funded projects and research networks and EU Members States. RESULTS: A list of ten candidate data collections for potential integration were identified and prioritised. A different level of relevance was attributed to the enhanced metadata and data elements (mandatory, recommended, optional) to allow for their flexible applicability by end users. These elements should be provided for reaching the required quality in the data documentation as well as for ensuring a correct data traceability and interpretation. CONCLUSIONS: The proposed enhanced metadata and data models of the IPCHEM thematic module "Products and Indoor Air Data" can be used by data providers when planning and setting up their future indoor air monitoring campaigns, or to further mapping and harmonising data elements of their existing data collections for further integration into IPCHEM. This will boost the effective implementation of a coordinated approach for collecting, accessing and sharing existing and future indoor air monitoring data in support of policy making.

Building a European exposure science strategy.

Exposure information is a critical element in various regulatory and non-regulatory frameworks in Europe and elsewhere. Exposure science supports to ensure safe environments, reduce human health risks, and foster a sustainable future. However, increasing diversity in regulations and the lack of a professional identity as exposure scientists currently hamper developing the field and uptake into European policy. In response, we discuss trends, and identify three key needs for advancing and harmonizing exposure science and its application in Europe. We provide overarching building blocks and define six long-term activities to address the identified key needs, and to iteratively improve guidelines, tools, data, and education. More specifically, we propose creating European networks to maximize synergies with adjacent fields and identify funding opportunities, building common exposure assessment approaches across regulations, providing tiered education and training programmes, developing an aligned and integrated exposure assessment framework, offering best practices guidance, and launching an exposure information exchange platform. Dedicated working groups will further specify these activities in a consistent action plan. Together, these elements form the foundation for establishing goals and an action roadmap for successfully developing and implementing a 'European Exposure Science Strategy' 2020-2030, which is aligned with advances in science and technology.

Current EU research activities on combined exposure to multiple chemicals.

Humans and wildlife are exposed to an intractably large number of different combinations of chemicals via food, water, air, consumer products, and other media and sources. This raises concerns about their impact on public and environmental health. The risk assessment of chemicals for regulatory purposes mainly relies on the assessment of individual chemicals. If exposure to multiple chemicals is considered in a legislative framework, it is usually limited to chemicals falling within this framework and co-exposure to chemicals that are covered by a different regulatory framework is often neglected. Methodologies and guidance for assessing risks from combined exposure to multiple chemicals have been developed for different regulatory sectors, however, a harmonised, consistent approach for performing mixture risk assessments and management across different regulatory sectors is lacking. At the time of this publication, several EU research projects are running, funded by the current European Research and Innovation Programme Horizon 2020 or the Seventh Framework Programme. They aim at addressing knowledge gaps and developing methodologies to better assess chemical mixtures, by generating and making available internal and external exposure data, developing models for exposure assessment, developing tools for in silico and in vitro effect assessment to be applied in a tiered framework and for grouping of chemicals, as well as developing joint epidemiological-toxicological approaches for mixture risk assessment and for prioritising mixtures of concern. The projects EDC-MixRisk, EuroMix, EUToxRisk, HBM4EU and SOLUTIONS have started an exchange between the consortia, European Commission Services and EU Agencies, in order to identify where new methodologies have become available and where remaining gaps need to be further addressed. This paper maps how the different projects contribute to the data needs and assessment methodologies and identifies remaining challenges to be further addressed for the assessment of chemical mixtures.

On the Development of Health-Based Ventilation Guidelines: Principles and Framework.

This paper summarizes the results of HealthVent project. It had an aim to develop health-based ventilation guidelines and through this process contribute to advance indoor air quality (IAQ) policies and guidelines. A framework that allows determining ventilation requirements in public and residential buildings based on the health requirements is proposed. The framework is based on three principles: 1. Criteria for permissible concentrations of specific air pollutants set by health authorities have to be respected; 2. Ventilation must be preceded by source control strategies that have been duly adopted to improve IAQ; 3. Base ventilation must always be secured to remove occupant emissions (bio-effluents). The air quality guidelines defined by the World Health Organization (WHO) outside air are used as the reference for determining permissible levels of the indoor air pollutants based on the principle that there is only one air. It is proposed that base ventilation should be set at 4 L/s per person; higher rates are to be used only if WHO guidelines are not followed. Implementation of the framework requires technical guidelines, directives and other legislation. Studies are also needed to examine the effectiveness of the approach and to validate its use. It is estimated that implementing the framework would bring considerable reduction in the burden of disease associated with inadequate IAQ.

A Spatial Data Infrastructure for Environmental Noise Data in Europe.

Access to high quality data is essential in order to better understand the environmental and health impact of noise in an increasingly urbanised world. This paper analyses how recent developments of spatial data infrastructures in Europe can significantly improve the utilization of data and streamline reporting on a pan-European scale. The Infrastructure for Spatial Information in the European Community (INSPIRE), and Environmental Noise Directive (END) described in this manuscript provide principles for data management that, once applied, would lead to a better understanding of the state of environmental noise. Furthermore, shared, harmonised and easily discoverable environmental spatial data, required by the INSPIRE, would also support the data collection needed for the assessment and development of strategic noise maps. Action plans designed by the EU Member States to reduce noise and mitigate related effects can be shared to the public through already established nodes of the European spatial data infrastructure. Finally, data flows regarding reporting on the state of environment and END implementation to the European level can benefit by applying a decentralised e-reporting service oriented infrastructure. This would allow reported data to be maintained, frequently updated and enable pooling of information from/to other relevant and interrelated domains such as air quality, transportation, human health, population, marine environment or biodiversity. We describe those processes and provide a use case in which noise data from two neighbouring European countries are mapped to common data specifications, defined by INSPIRE, thus ensuring interoperability and harmonisation.

Reducing burden of disease from residential indoor air exposures in Europe (HEALTHVENT project).

BACKGROUND: The annual burden of disease caused indoor air pollution, including polluted outdoor air used to ventilate indoor spaces, is estimated to correspond to a loss of over 2 million healthy life years in the European Union (EU). Based on measurements of the European Environment Agency (EEA), approximately 90 % of EU citizens live in areas where the World Health Organization (WHO) guidelines for air quality of particulate matter sized < 2.5 mm (PM2.5) are not met. Since sources of pollution reside in both indoor and outdoor air, selecting the most appropriate ventilation strategy is not a simple and straightforward task. METHODS: A framework for developing European health-based ventilation guidelines was created in 2010-2013 in the EU-funded HEALTHVENT project. As a part of the project, the potential efficiency of control policies to health effects caused by residential indoor exposures of fine particulate matter (PM2.5), outdoor bioaerosols, volatile organic compounds (VOC), carbon oxide (CO) radon and dampness was estimated. The analysis was based on scenario comparison, using an outdoor-indoor mass-balance model and varying the ventilation rates. Health effects were estimated with burden of diseases (BoD) calculations taking into account asthma, cardiovascular (CV) diseases, acute toxication, respiratory infections, lung cancer and chronic obstructive pulmonary disease (COPD). RESULTS: The quantitative comparison of three main policy approaches, (i) optimising ventilation rates only; (ii) filtration of outdoor air; and (iii) indoor source control, showed that all three approaches are able to provide substantial reductions in the health risks, varying from approximately 20 % to 44 %, corresponding to 400 000 and 900 000 saved healthy life years in EU-26. PM2.5 caused majority of the health effects in all included countries, but the importance of the other pollutants varied by country. CONCLUSIONS: The present modelling shows, that combination of controlling the indoor air sources and selecting appropriate ventilation rate was the most effective to reduce health risks. If indoor sources cannot be removed or their emissions cannot be limited to an accepted level, ventilation needs to be increased to remove remaining pollutants. In these cases filtration of outdoor air may be needed to prevent increase of health risks.

Advances in the development of common noise assessment methods in Europe: The CNOSSOS-EU framework for strategic environmental noise mapping.

The Environmental Noise Directive (2002/49/EC) requires EU Member States to determine the exposure to environmental noise through strategic noise mapping and to elaborate action plans in order to reduce noise pollution, where necessary. A common framework for noise assessment methods (CNOSSOS-EU) has been developed by the European Commission in co-operation with the EU Member States to be applied for strategic noise mapping as required by the Environment Noise Directive (2002/49/EC). CNOSSOS-EU represents a harmonised and coherent approach to assess noise levels from the main sources of noise (road traffic, railway traffic, aircraft and industrial) across Europe. This paper outlines the process behind the development of CNOSSOS-EU and the parts of the CNOSSOS-EU core methodological framework which were developed during phase A of the CNOSSOS-EU process (2010-2012), whilst focusing on the main scientific and technical issues that were addressed, and the implementation challenges that are being faced before it can become fully operational in the EU MS.

Evaluation of the fate of the active ingredients of insecticide sprays used indoors.

The fate of the active ingredients of insecticide sprays after use in indoor environments was investigated. Indoor air sampling was performed through two types of adsorbents, namely, TENAX TA and XAD-2 (10 L). After sampling, both adsorbents were ultrasonically extracted and analyzed by Gas Chromatography coupled to Mass Spectroscopy. The separation and analysis of the selected compounds were satisfactory and fast (duration of the chromatographic run: 40 min). The method was linear for all examined chemicals over the tested range (2 to 50 ng of absolute compound); limits of detection ranged from 0.42 to 1.32 ng of absolute compound. The method was then applied in the determination of the active ingredients of three commercially available insecticide sprays that were separately used in a full-scale environmental chamber (30 m(3)). After spraying, the fate of the active ingredients [propoxur, piperonyl butoxide (PBO) and pyrethrin insecticides] was monitored over 40 minutes, with and without ventilation. Both adsorbent materials were proven to be efficient and the differences in the concentrations deriving from sampling with both materials were in almost all cases less than 10%. All chemicals were removed in rates that exceeded 80%, after the 40 minutes of monitoring, exhibiting different decay rates. The removal of insecticides was not significantly affected by the ventilation of the chamber. The correlation analysis of propoxur, PBO and pyrethrins with the aerosols of various sizes (15 fractions, from 0.3 to > 20 microm) showed that propoxur and PBO mainly associated with the medium size aerosols (3-7.5 microm) while pyrethrins seem to link more with heavier particles (> 10 microm).

Characterisation of urban inhalation exposures to benzene, formaldehyde and acetaldehyde in the European Union: comparison of measured and modelled exposure data.

BACKGROUND, AIM AND SCOPE: All across Europe, people live and work in indoor environments. On average, people spend around 90% of their time indoors (homes, workplaces, cars and public transport means, etc.) and are exposed to a complex mixture of pollutants at concentration levels that are often several times higher than outdoors. These pollutants are emitted by different sources indoors and outdoors and include volatile organic compounds (VOCs), carbonyls (aldehydes and ketones) and other chemical substances often adsorbed on particles. Moreover, legal obligations opposed by legislations, such as the European Union's General Product Safety Directive (GPSD) and Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), increasingly require detailed understanding of where and how chemical substances are used throughout their life-cycle and require better characterisation of their emissions and exposure. This information is essential to be able to control emissions from sources aiming at a reduction of adverse health effects. Scientifically sound human risk assessment procedures based on qualitative and quantitative human exposure information allows a better characterisation of population exposures to chemical substances. In this context, the current paper compares inhalation exposures to three health-based EU priority substances, i.e. benzene, formaldehyde and acetaldehyde. MATERIALS AND METHODS: Distributions of urban population inhalation exposures, indoor and outdoor concentrations were created on the basis of measured AIRMEX data in 12 European cities and compared to results from existing European population exposure studies published within the scientific literature. By pooling all EU city personal exposure, indoor and outdoor concentration means, representative EU city cumulative frequency distributions were created. Population exposures were modelled with a microenvironment model using the time spent and concentrations in four microenvironments, i.e. indoors at home and at work, outdoors at work and in transit, as input parameters. Pooled EU city inhalation exposures were compared to modelled population exposures. The contributions of these microenvironments to the total daily inhalation exposure of formaldehyde, benzene and acetaldehyde were estimated. Inhalation exposures were compared to the EU annual ambient benzene air quality guideline (5 microg/m3-to be met by 2010) and the recommended (based on the INDEX project) 30-min average formaldehyde limit value (30 microg/m3). RESULTS: Indoor inhalation exposure contributions are much higher compared to the outdoor or in-transit microenvironment contributions, accounting for almost 99% in the case of formaldehyde. The highest in-transit exposure contribution was found for benzene; 29.4% of the total inhalation exposure contribution. Comparing the pooled AIRMEX EU city inhalation exposures with the modelled exposures, benzene, formaldehyde and acetaldehyde exposures are 5.1, 17.3 and 11.8 microg/m3 vs. 5.1, 20.1 and 10.2 microg/m3, respectively. Together with the fact that a dominating fraction of time is spent indoors (>90%), the total inhalation exposure is mostly driven by the time spent indoors. DISCUSSION: The approach used in this paper faced three challenges concerning exposure and time-activity data, comparability and scarce or missing in-transit data inducing careful interpretation of the results. The results obtained by AIRMEX underline that many European urban populations are still exposed to elevated levels of benzene and formaldehyde in the inhaled air. It is still likely that the annual ambient benzene air quality guideline of 5 microg/m3 in the EU and recommended formaldehyde 30-min average limit value of 30 microg/m3 are exceeded by a substantial part of populations living in urban areas. Considering multimedia and multi-pathway exposure to acetaldehyde, the biggest exposure contribution was found to be related to dietary behaviour rather than to inhalation. CONCLUSIONS: In the present study, inhalation exposures of urban populations were assessed on the basis of novel and existing exposure data. The indoor residential microenvironment contributed most to the total daily urban population inhalation exposure. The results presented in this paper suggest that a significant part of the populations living in European cities exceed the annual ambient benzene air quality guideline of 5 microg/m3 in the EU and recommended (INDEX project) formaldehyde 30-min average limit value of 30 microg/m3. RECOMMENDATIONS AND PERSPECTIVES: To reduce exposures and consequent health effects, adequate measures must be taken to diminish emissions from sources such as materials and products that especially emit benzene and formaldehyde in indoor air. In parallel, measures can be taken aiming at reducing the outdoor pollution contribution indoors. Besides emission reduction, mechanisms to effectively monitor and manage the indoor air quality should be established. These mechanisms could be developed by setting up appropriate EU indoor air guidelines.

Issues in consumer exposure modeling: towards harmonization on a global scale.

Understanding where and how chemicals are used throughout their life cycle is becoming increasingly important. In 2003, within the context of REACH and GPSD legislation, the European Commission started developing a European and global infrastructure of exposure methods and tools. The infrastructure aims (1) to link modeling tools and exposure-related data and scenarios in a single framework so that harmonized exposure assessment procedures can be developed for consumer products in the EU and (2) to make this framework flexible enough to allow global application. A number of issues are raised by a global infrastructure of consumer exposure modeling that answers to multi-legislative mandates. These include transparency, consistency, usability, and defensibility of the models, including the relevant degree of complexity for priority setting versus assessment. As part of the initiative to set up a harmonized global infrastructure on consumer exposure assessment, these issues were presented, discussed, and further developed in a series of European Commission-sponsored workshops organized in October 2004 and June 2005 as part of the "Harmonization of Consumer Exposure Models on a Global Scale" project. The project focused on development, harmonization, and validation of consumer exposure modeling approaches. The workshops included experts from the EU, USA, Japan, and Canada. The conclusions and recommendations made on the basis of this work are described. To help achieve harmonization of approaches, the European Commission's Joint Research Centre is proposing a framework (1) to compare information on elements of chemical risk assessment to understand exposure regulations in different countries, (2) to save time and expense by sharing information and models, and (3) to promote credible science through better communication among organizations and by peer review of assessments and assessment procedures.

Personal carbon monoxide exposure levels: contribution of local sources to exposures and microenvironment concentrations in Milan.

In the framework of the EXPOLIS study in Milan, Italy, 48-h carbon monoxide (CO) exposures of 50 office workers were monitored over a 1-year period. In this work, the exposures were assessed for different averaging times and were compared with simultaneous ambient fixed-site concentrations. The effect of gas cooking and smoking and different methods of commuting on the microenvironment and exposure levels of CO were investigated. During the sampling the subjects completed a time-microenvironment-activity diary differentiating 11 microenvironments and three exposure influencing activities: gas cooking, smoking and commuting. After sampling, all exposure and time allocation data were stored in a relational database that is used in data analyses. Ambient 48-h and maximum 8-h distributions were similar compared to the respective personal exposures. The maximum 1-h personal exposures were much higher than the maximum 8-h exposures. The maximum 1-h exposures were as well higher than the corresponding ambient distribution. These findings indicate that high short-term exposures were not reflected in ambient monitoring data nor by long-term exposures. When gas cooking or smoking was present, the indoor levels at "home-" and in "other indoor" microenvironments were higher than without their presence. Compared with ambient data, the latter source was the most affective to increase the indoor levels. Exposure during commuting was higher than in all other microenvironments; the highest daily exposure contribution was found during "car/taxi" driving. Most of the CO exposure is acquired in indoor microenvironments. For the indoor microenvironments, ambient CO was the weakest predictor for "home indoor" concentrations, where the subjects spent most of their time, and the strongest for "other indoor" concentrations, where the smallest fraction of the time was spent. Of the main indoor sources, gas cooking, on average, significantly raised the indoor exposure concentrations for 45 min and tobacco smoking for 30 min. The highest exposure levels were experienced in street commuting. Personal exposures were well predicted, but 1-h maximum personal exposures were poorly predicted, by respective ambient air quality data. By the use of time-activity diaries, ETS exposure at the workplaces were probably misclassified due to differences in awareness to tobacco smoke between smokers and nonsmokers.

Simulation of working population exposures to carbon monoxide using EXPOLIS-Milan microenvironment concentration and time-activity data.

Current air pollution levels have been shown to affect human health. Probabilistic modeling can be used to assess exposure distributions in selected target populations. Modeling can and should be used to compare exposures in alternative future scenarios to guide society development. Such models, however, must first be validated using existing data for a past situation. This study applied probabilistic modeling to carbon monoxide (CO) exposures using EXPOLIS-Milan data. In the current work, the model performance was evaluated by comparing modeled exposure distributions to observed ones. Model performance was studied in detail in two dimensions; (i) for different averaging times (1, 8 and 24 h) and (ii) using different detail in defining the microenvironments in the model (two, five and 11 microenvironments). (iii) The number of exposure events leading to exceeding the 8-h guideline was estimated. Population time activity was modeled using a fractions-of-time approach assuming that some time is spent in each microenvironment used in the model. This approach is best suited for averaging times from 24 h upwards. In this study, we tested how this approach affects results when used for shorter averaging times, 1 and 8 h. Models for each averaging time were run with two, five and 11 microenvironments. The two-microenvironment models underestimated the means and standard deviations (SDs) slightly for all averaging times. The five- and 11-microenvironment models matched the means quite well but underestimated SDs in several cases. For 1- and 24-h averaging times the simulated SDs are slightly smaller than the corresponding observed values. The 8-h model matched the observed exposure levels best. The results show that for CO (i) the modeling approach can be applied for averaging times from 8 to 24 h and as a screening model even to an averaging time of 1 h; (ii) the number of microenvironments affects only weakly the results and in the studied cases only exposure levels below the 80th percentile; (iii) this kind of model can be used to estimate the number of high-exposure events related to adverse health effects. By extrapolation beyond the observed data, it was shown that Milanese office workers may experience adverse health effects caused by CO.