Very dense pollutant emissions over megacities (large urban agglomerations with more than about 7 millions of inhabitants) are strongly affecting air quality on an urban scale and chemical composition on a regional and even global scale. This ultimately affects both public health and regional to global climate. In order to assess the overall effects of megacity emissions, all links between emissions, transport, chemical transformation and deposition processes should be well understood, which is currently not yet true. In particular, despite its adverse effects on health and their climate effect, primary and secondary sources of particulate matter, and in particular of organic aerosol in the urban atmosphere are not well qualified and quantified. The project MEGAPOLI-PARIS aims at gaining an increasing comprehension of major processes affecting the abundance of particulate matter in a polluted atmosphere, in particular : ' to better assess primary sources of carbonaceous aerosols, ' to better assess secondary sources of organic aerosols through gas-to-particle conversion, ' using this knowledge, to evaluate and improve process and air quality models. The first major objective of the project deals with closing identified knowledge gaps and to provide experimental data for model improvement and evaluation. This concerns in particular formation processes of primary and secondary aerosol at regional scale, with a specific focus on organic matter, for which urban sources are not well quantified. A number of specific objectives will be pursued: ' to document the aerosol composition and properties, and gaseous precursor concentrations, within a large agglomeration and in its plume, with a focus on the chemical speciation of organic carbon; the defined target area is the Ile de France region, ' to provide source apportionment of elemental and organic carbon PM, in order to improve regional scale emission inventories, ' to document pathways of secondary organic aerosol build-up from gaseous precursors within the agglomeration and in its plume, ' to use experimental data obtained through the project and already existing data bases in order to evaluate and to improve process (0D) and air quality (3D) models for a large range of conditions (effective emission strength, meteorological variables). Greater Paris has been chosen as a playground for investigating theses aspects, because it is a major and densely populated pollution source (more than 10 million inhabitants), surrounded by rural areas and relatively flat terrain. Therefore, a dedicated field campaign is designed over the Greater Paris to allow for the characterisation of the aerosol pollution in large urban areas. In addition, the facility of campaign logistics (established co-operations for access to campaign sites, vicinity of research labs, presence of a very well established air quality survey network), as compared to an extra-European megacity, was taken into account for the choice. During the campaign, two (one urban and one sub-urban) super-sites will be set-up during one summer and winter month each. In addition, two mobile laboratories will allow sampling the pollution plume and upwind conditions. Finally, dedicated aircraft measurements will allow following the chemical composition of the polluted plume. Given the variety of platforms and the state of the art character of deployed instrumentation, this is the most detailed aerosol characterisation experiment perform so far in an urban environment over Europe. As a second overall objective, the system's sensitivity with respect to anthropogenic forcing and the impact of mitigation strategies will be evaluated. This work will be performed with 0D process and 3D air quality models, which will have been carefully evaluated and improved using the in particular the campaign observations. Sensitivity analysis will address different chemical families of aerosol and size ranges, and will investigate dependence on both emission flux from individual sources and on meteorological variables. This is prerequisite to elaborate and to evaluate mitigation strategies to control the health risk of particulate matter pollution under different scenarios. Considering the generally trans-boundary nature of particulate pollution episodes, it is relevant to consider emission reduction strategies that should be applied at the European, in addition to specific urban scale scenarios.

The quality of the air we breathe is a central concern of individuals living in urban and suburban areas. Millions of people are exposed every day to air pollution at high levels. The impact of such pollution on the human health is extremely alarming. Particularly, WHO and IARC have classified air pollution, including fine particles, as certain carcinogenic. Understanding the totality of exposures to air pollutants over the course of our daily life is a key concern to reduce the risk of some major diseases. However, the ability to acquire high-quality, relevant, and useful individual’s exposure data is challenging. Currently available air pollution fixed station networks allow to only account for background air pollution and less frequently proximity air pollution from road traffic. As a result, the measurements made through this kind of network typically provide the average exposure to air pollution in a specific geographical zone. In particular, they fall short to quantify the real individual’s exposure with respect to his/her indoor/outdoor daily life activities in different settings, such as transport, work, dwellings, etc. Nowadays, an increasing number of wearable and lightweight environmental sensors have emerged, enabling a continuum measurement of the real personal exposure anywhere at anytime. Such an evolution has been the main enabler of providing new solutions for data acquisition, namely community-based participatory sensing where citizens contribute data to the system with the purpose of sharing events of interest within the community. This technology has recently gained a great interest among the actors of environmental science in public, associative, and private sectors, while stimulating a wide range of research projects worldwide. Building on top of such a technology evolution, Polluscope aims at bringing together experts from environmental, metrology, epidemiological, and data sciences while providing methodologies, techniques, and tools – expected to drastically change the way individual’s exposure and exposure variability are measured, perceived, and evaluated. Such measurements will not only consider gaseous pollutants (Ozone, NO2), but also particulates (via particulate matter and black carbon) and those typical of indoor environments (VOC) – providing a representative overview of the air pollution. Gaining such enriched insights into individual’s exposure will contribute towards reducing individual risks of some diseases by changing their behavior. This will end up in a solid, invaluable, and vital societal impact namely, saving life and improving the individual well-being. To achieve these objectives, a novel infrastructure for real individual’s exposure data acquisition, processing, and analysis will be develope. For this to be done, several scientific and technical challenges come into the picture. The data are collected at a high frequency and might be massive and noisy. Therefore, the system must be able to process them efficiently, while taking into account both their velocity and their uncertainty. More importantly, it has to offer microenvironment and user’s activity recognition, through integration with external spatiotemporal resources. An efficient data collection and analysis will provide an insightful knowledge on individual’s exposure over his/her daily life activities, and will enable conducting analytical queries, novel risk assessment modeling, mining and comparing profiles of pollution exposures, and so on. Therefore, it is evident that a robust, efficient, and powerful data science technology is crucial. Lastly, Polluscope will be evaluated under real-world use cases. Several type of population will be targeted by the data acquisition campaign. Both diseased and healthy subjects will be involved to conduct an epidemiological study relating air pollution exposure to health on the one hand, and volunteer participants for the crowd sensing on the other hand.