Long-term measurements of greenhouse and reactive gases, and aerosols, at Saclay/SIRTA observatory in the Ile de France Region as part of ICOS and ACTRIS

Today, around 7 million deaths a year worldwide are linked to air pollution. Moreover, urban planning projections show that by 2050, there will be 2 billion more people in cities, further increasing the contribution of cities to rising CO₂ emissions. In addition, this could lead to health problems linked to deteriorating air quality.

Our study focuses on the city of Paris and the Ile de France region, where the main pollutant and CO₂ emission sectors are road traffic and the residential sector. Depending on the emission sector, there is co-emission between pollutants and greenhouse gases which can be used to link atmospheric observations of those components to a particular sector. This so-called multi-component atmospheric approach can therefore complement the information provided by sectorial inventories. This study uses data measured on the Saclay peri-urban site to analyze long-term time series of CO₂ and pollutants with meteorological conditions and surface emissions.

At Saclay, the ACTRIS SIRTA station measures reactive gases, and aerosol while the ICOS tall tower measures greenhouse gases. The two stations are not co-located but are only 2 km apart. The compounds chosen for this study are CO₂, CO, CH₄, from the ICOS tower, and NOx, O₃, and black carbon (BC) from the SIRTA site. The BC has been separated into wood burning (BCwb) and fossil fuel (BCff) contributions. The data from the two stations cover more than ten years of measurements for all the compounds mentioned. Since Saclay is located about 20km from southwest Paris, it was necessary to distinguish between two geographical sectors. An urban sector with the main contribution from Paris and a rural sector for comparison with concentrations close to background levels. The two sectors account for more than 44% of total data.

The diurnal cycles of the studied compounds show similar patterns in the urban and rural sectors but with very contrasted amplitudes. The NO₂, BCff, and CO cycles in the urban sector are strongly driven by the traffic with morning and evening peaks corresponding to the rush hours. On the other hand, BCwb diurnal cycle peaks mainly in the evening as expected with the timing of the residential heating, and contrary to other species the amplitudes of the maximum are higher in the rural sector. This can be explained by the larger use of wood burning in the rural areas, whereas it is strictly regulated in Paris.

The diurnal cycle of CO₂ peaks in the morning mainly due to photosynthesis, but a share comes from emissions from transport or the tertiary sector. Species ratios, such as CO/CO₂ and NO₂/CO₂, are calculated for further study and comparison with emission inventories.

The study will also include analysis of seasonal cycles and long-term trends for the two geographical sectors.