Florian Couvidat

The dependency of emission and atmospheric physicochemical processes on various meteorological drivers are often not completely accounted for by 3D air quality models. In order to tackle this issue, the present study assesses weather-driven trends in atmospheric emissions and air quality in Europe over 1990–2022 using an enhanced version of the CHIMERE chemical transport model. The model includes meteorology-dependent anthropogenic emissions, varying 8-day leaf area index from satellite data over the whole period, and updated parameterizations for deposition as well as soil and biogenic emissions. Simulations performed with constant anthropogenic emission practices indicate significant increases in biogenic VOC, ammonia, and soil NOx emissions. In contrast, emissions decrease for the residential sector and road traffic NOx, due to warmer temperatures reducing heating and cold-start emissions. Ozone annual concentrations show regionally contrasting trends, with increases in southern Europe but decreases in northern regions due to enhanced deposition linked to vegetation changes. Significant increases, driven mainly by rising temperatures and solar radiation, are simulated for SOMO35 and AOT40c, with population-weighted trends of 0.5 %/yr and 0.69 %/yr, corresponding to overall increases by 18 % and 22 % over the 1990–2022 period, respectively. Fine particulate matter generally declines (population-weighted trend of -0.03 µg/m³/yr, +0.95 µg/m³/yr over the period), despite increases in secondary organic aerosols and bioaerosols. Reduced nitrogen deposition also increased (+3.9 kT/yr, around +4.8 % over the period) due to increases in ammonia gas-phase fraction and emissions.

Recent experimental and theoretical work has highlighted missing pathways in the oxidation of aromatic compounds, with consequences for the formation of highly oxygenated products relevant to secondary organic aerosol (SOA) formation. In this study we develop an updated, quasi-explicit oxidation mechanism for benzene based on Master Chemical Mechanism (MCM) v3.3.1, extended to represent key multi-generation chemistry. Quantum chemical calculations are used to derive the formation and evolution of geminal-diol bicyclic peroxy radicals and to parameterize the subsequent molecular rearrangements. The mechanism further incorporates autoxidation sequences previously developed for peroxy and alkoxy radicals, successive OH additions and cyclic epoxides formation. This approach enables a more mechanistic description of aromatic oxidation leading to highly oxygenated, low-volatility products. The mechanism is evaluated using box-model simulations against a set of chamber experiments conducted under various conditions. Simulated aerosol concentrations agree well with observations and emphasize the dominant contribution of the newly implemented pathways. The quasi-explicit mechanism is subsequently reduced using the GENerator of reduced Organic Aerosol mechanisms (GENOA), resulting in a semi-explicit mechanism reduced to 1 % of its original number of species while reproducing SOA mass with a mean error of 3.9 % relative to the quasi-explicit scheme. Using the validated reduced mechanism, zero-dimensional simulations under contrasted atmospheric conditions are conducted to estimate the SOA compounds that are formed in the early stages of oxidation and those that dominate the system at later stages.

Recent experimental and theoretical work has highlighted missing pathways in the oxidation of aromatic compounds, with consequences for the formation of highly oxygenated products relevant to secondary organic aerosol (SOA) formation. In this study we develop an updated, quasi-explicit oxidation mechanism for benzene based on Master Chemical Mechanism (MCM) v3.3.1, extended to represent key multi-generation chemistry. Quantum chemical calculations are used to derive the formation and evolution of geminal-diol bicyclic peroxy radicals and to parameterize the subsequent molecular rearrangements. The mechanism further incorporates autoxidation sequences previously developed for peroxy and alkoxy radicals, successive OH additions and cyclic epoxides formation. This approach enables a more mechanistic description of aromatic oxidation leading to highly oxygenated, low-volatility products. The mechanism is evaluated using box-model simulations against a set of chamber experiments conducted under various conditions. Simulated aerosol concentrations agree well with observations and emphasize the dominant contribution of the newly implemented pathways. The quasi-explicit mechanism is subsequently reduced using the GENerator of reduced Organic Aerosol mechanisms (GENOA), resulting in a semi-explicit mechanism reduced to 1 % of its original number of species while reproducing SOA mass with a mean error of 3.9 % relative to the quasi-explicit scheme. Using the validated reduced mechanism, zero-dimensional simulations under contrasted atmospheric conditions are conducted to estimate the SOA compounds that are formed in the early stages of oxidation and those that dominate the system at later stages.

Recent experimental and theoretical work has highlighted missing pathways in the oxidation of aromatic compounds, with consequences for the formation of highly oxygenated products relevant to secondary organic aerosol (SOA) formation. In this study we develop an updated, quasi-explicit oxidation mechanism for benzene based on Master Chemical Mechanism (MCM) v3.3.1, extended to represent key multi-generation chemistry. Quantum chemical calculations are used to derive the formation and evolution of geminal-diol bicyclic peroxy radicals and to parameterize the subsequent molecular rearrangements. The mechanism further incorporates autoxidation sequences previously developed for peroxy and alkoxy radicals, successive OH additions and cyclic epoxides formation. This approach enables a more mechanistic description of aromatic oxidation leading to highly oxygenated, low-volatility products. The mechanism is evaluated using box-model simulations against a set of chamber experiments conducted under various conditions. Simulated aerosol concentrations agree well with observations and emphasize the dominant contribution of the newly implemented pathways. The quasi-explicit mechanism is subsequently reduced using the GENerator of reduced Organic Aerosol mechanisms (GENOA), resulting in a semi-explicit mechanism reduced to 1 % of its original number of species while reproducing SOA mass with a mean error of 3.9 % relative to the quasi-explicit scheme. Using the validated reduced mechanism, zero-dimensional simulations under contrasted atmospheric conditions are conducted to estimate the SOA compounds that are formed in the early stages of oxidation and those that dominate the system at later stages.

The dependency of emission and atmospheric physicochemical processes on various meteorological drivers are often not completely accounted for by 3D air quality models. In order to tackle this issue, the present study assesses weather-driven trends in atmospheric emissions and air quality in Europe over 1990–2022 using an enhanced version of the CHIMERE chemical transport model. The model includes meteorology-dependent anthropogenic emissions, varying 8-day leaf area index from satellite data over the whole period, and updated parameterizations for deposition as well as soil and biogenic emissions. Simulations performed with constant anthropogenic emission practices indicate significant increases in biogenic VOC, ammonia, and soil NOx emissions. In contrast, emissions decrease for the residential sector and road traffic NOx, due to warmer temperatures reducing heating and cold-start emissions. Ozone annual concentrations show regionally contrasting trends, with increases in southern Europe but decreases in northern regions due to enhanced deposition linked to vegetation changes. Significant increases, driven mainly by rising temperatures and solar radiation, are simulated for SOMO35 and AOT40c, with population-weighted trends of 0.5 %/yr and 0.69 %/yr, corresponding to overall increases by 18 % and 22 % over the 1990–2022 period, respectively. Fine particulate matter generally declines (population-weighted trend of -0.03 µg/m3/yr, +0.95 µg/m3/yr over the period), despite increases in secondary organic aerosols and bioaerosols. Reduced nitrogen deposition also increased (+3.9 kT/yr, around +4.8 % over the period) due to increases in ammonia gas-phase fraction and emissions.

Recent experimental and theoretical work has highlighted missing pathways in the oxidation of aromatic compounds, with consequences for the formation of highly oxygenated products relevant to secondary organic aerosol (SOA) formation. In this study we develop an updated, quasi-explicit oxidation mechanism for benzene based on Master Chemical Mechanism (MCM) v3.3.1, extended to represent key multi-generation chemistry. Quantum chemical calculations are used to derive the formation and evolution of geminal-diol bicyclic peroxy radicals and to parameterize the subsequent molecular rearrangements. The mechanism further incorporates autoxidation sequences previously developed for peroxy and alkoxy radicals, successive OH additions and cyclic epoxides formation. This approach enables a more mechanistic description of aromatic oxidation leading to highly oxygenated, low-volatility products. The mechanism is evaluated using box-model simulations against a set of chamber experiments conducted under various conditions. Simulated aerosol concentrations agree well with observations and emphasize the dominant contribution of the newly implemented pathways. The quasi-explicit mechanism is subsequently reduced using the GENerator of reduced Organic Aerosol mechanisms (GENOA), resulting in a semi-explicit mechanism reduced to 1 % of its original number of species while reproducing SOA mass with a mean error of 3.9 % relative to the quasi-explicit scheme. Using the validated reduced mechanism, zero-dimensional simulations under contrasted atmospheric conditions are conducted to estimate the SOA compounds that are formed in the early stages of oxidation and those that dominate the system at later stages.

Recent experimental and theoretical work has highlighted missing pathways in the oxidation of aromatic compounds, with consequences for the formation of highly oxygenated products relevant to secondary organic aerosol (SOA) formation. In this study we develop an updated, quasi-explicit oxidation mechanism for benzene based on Master Chemical Mechanism (MCM) v3.3.1, extended to represent key multi-generation chemistry. Quantum chemical calculations are used to derive the formation and evolution of geminal-diol bicyclic peroxy radicals and to parameterize the subsequent molecular rearrangements. The mechanism further incorporates autoxidation sequences previously developed for peroxy and alkoxy radicals, successive OH additions and cyclic epoxides formation. This approach enables a more mechanistic description of aromatic oxidation leading to highly oxygenated, low-volatility products. The mechanism is evaluated using box-model simulations against a set of chamber experiments conducted under various conditions. Simulated aerosol concentrations agree well with observations and emphasize the dominant contribution of the newly implemented pathways. The quasi-explicit mechanism is subsequently reduced using the GENerator of reduced Organic Aerosol mechanisms (GENOA), resulting in a semi-explicit mechanism reduced to 1 % of its original number of species while reproducing SOA mass with a mean error of 3.9 % relative to the quasi-explicit scheme. Using the validated reduced mechanism, zero-dimensional simulations under contrasted atmospheric conditions are conducted to estimate the SOA compounds that are formed in the early stages of oxidation and those that dominate the system at later stages.

Recent experimental and theoretical work has highlighted missing pathways in the oxidation of aromatic compounds, with consequences for the formation of highly oxygenated products relevant to secondary organic aerosol (SOA) formation. In this study we develop an updated, quasi-explicit oxidation mechanism for benzene based on Master Chemical Mechanism (MCM) v3.3.1, extended to represent key multi-generation chemistry. Quantum chemical calculations are used to derive the formation and evolution of geminal-diol bicyclic peroxy radicals and to parameterize the subsequent molecular rearrangements. The mechanism further incorporates autoxidation sequences previously developed for peroxy and alkoxy radicals, successive OH additions and cyclic epoxides formation. This approach enables a more mechanistic description of aromatic oxidation leading to highly oxygenated, low-volatility products. The mechanism is evaluated using box-model simulations against a set of chamber experiments conducted under various conditions. Simulated aerosol concentrations agree well with observations and emphasize the dominant contribution of the newly implemented pathways. The quasi-explicit mechanism is subsequently reduced using the GENerator of reduced Organic Aerosol mechanisms (GENOA), resulting in a semi-explicit mechanism reduced to 1 % of its original number of species while reproducing SOA mass with a mean error of 3.9 % relative to the quasi-explicit scheme. Using the validated reduced mechanism, zero-dimensional simulations under contrasted atmospheric conditions are conducted to estimate the SOA compounds that are formed in the early stages of oxidation and those that dominate the system at later stages.