Air pollution, especially in urban areas, is the result of a complex mixture of natural and anthropogenic emissions and their atmospheric processing. It causes millions of premature deaths worldwide and affects plant metabolism, which in turn alters the emissions of Biogenic Volatile Organic Compound (BVOCs) by plants. By taking the subtropical Metropolitan Area of São Paulo (MASP) as a natural laboratory, the BIOMASP+ project (BIOsphere-atmosphere interactions in the Metropolitan Area of São Paulo - plus ) aims to evaluate the interplay between the biosphere and secondary pollution (ozone and SOA formation and aging). The Brazilian Atlantic Forest (Mata Atlântica) is the target ecosystem as the fifth biodiversity hotspot in the world. Here we present the scientific motivations of the project, its methodology and the preliminary observations from the Special Observation Periods of year 2023 (SOP1, 2, 3 and 4). BIOMASP+ is (i) integrative, by combining in-situ/remote/laboratory observations and modeling, (ii) multidisciplinary, addressing micrometeorology, urban climate, atmospheric chemistry and biology. The project involves multiple nested scales: from leaf to above-canopy levels, from very short time (microseconds) to multi-year scale, from few millimeters (turbulence scale) to synoptic scale. In particular, the experimental effort relies on the implementation of two contrasting supersites (primary forest and urban forest) with a 30-m and 20-m flux towers, respectively, and a variety of state-of-the-art instruments. Ambient observations and the quantification of BVOC emissions have highlighted the complex interactions between meteorology, atmospheric composition of pollution, biogenic emissions of representative remnants of the Atlantic Forest and anthropogenic emissions.

Carbonaceous aerosols (CA), composed of black carbon (BC) and organic matter (OM), significantly impact the climate. Light absorption properties of CA, particularly of BC and brown carbon (BrC), are crucial due to their contribution to global and regional warming. We present the absorption properties of BC (b(Abs,BC)) and BrC (b(Abs,BrC)) inferred using Aethalometer data from 44 European sites covering different environments (traffic (TR), urban (UB), suburban (SUB), regional background (RB) and mountain (M)). Absorption coefficients showed a clear relationship with station setting decreasing as follows: TR > UB > SUB > RB > M, with exceptions. The contribution of b(Abs,BrC) to total absorption (b(Abs)), i.e. %Abs(BrC), was lower at traffic sites (11-20 %), exceeding 30 % at some SUB and RB sites. Low AAE values were observed at TR sites, due to the dominance of internal combustion emissions, and at some remote RB/M sites, likely due to the lack of proximity to BrC sources, insufficient secondary processes generating BrC or the effect of photobleaching during transport. Higher b(Abs) and AAE were observed in Central/Eastern Europe compared to Western/Northern Europe, due to higher coal and biomass burning emissions in the east. Seasonal analysis showed increased b(Abs), b(Abs,BC), b(Abs,BrC) in winter, with stronger %Abs(BrC), leading to higher AAE. Diel cycles of b(Abs,BC) peaked during morning and evening rush hours, whereas b(Abs,BrC), %Abs(BrC), AAE, and AAE(BrC) peaked at night when emissions from household activities accumulated. Decade-long trends analyses demonstrated a decrease in b(Abs), due to reduction of BC emissions, while b(Abs,BrC) and AAE increased, suggesting a shift in CA composition, with a relative increase in BrC over BC. This study provides a unique dataset to assess the BrC effects on climate and confirms that BrC can contribute significantly to UV-VIS radiation presenting highly variable absorption properties in Europe.

The complex refractive index (CRI; n−ik) and the single scattering albedo (SSA) are key parameters driving the aerosol direct radiative effect. Their spatial, temporal, and spectral variabilities in anthropogenic–biogenic mixed environments are poorly understood. In this study, we retrieve the spectral CRI and SSA (370–950 nm wavelength range) from in situ surface optical measurements and the number size distribution of submicron aerosols at three sites in the greater Paris area, representative of the urban city, as well as its peri-urban and forested rural environments. Measurements were taken as part of the ACROSS (Atmospheric Chemistry of the Suburban Forest) campaign in June–July 2022 under diversified conditions: (1) two heatwaves leading to high aerosol levels, (2) an intermediate period with low aerosol concentrations, and (3) an episode of long-range-transported fire emissions. The retrieved CRI and SSA exhibit an urban-to-rural gradient, whose intensity is modulated by the weather conditions. A full campaign average CRI of 1.41−0.037i (urban), 1.52−0.038i (peri-urban), and 1.50−0.025i (rural) is retrieved. The imaginary part of the CRI (k) increases and the SSA decreases at the peri-urban and forest sites when exposed to the influence of the Paris urban plume. Values of k > 0.1 and SSA < 0.6 at 520 nm are related to a black carbon mass fraction larger than 10 %. Organic aerosols are found to contribute to more than 50 % of the aerosol mass and up to 10 % (urban), 17 % (peri-urban), and 22 % (forest) of the aerosol absorption coefficient at 370 nm. A k value of 0.022 (370 nm) was measured at the urban site for the long-range-transported fire episode.

Among the regulated sources of pollutants, shipping has a significant contribution to NOx and SO2 global emissions 1–3. The international maritime transport regulation was updated in 2020 lowering the sulphur content in marine fuel globally from 3.5% to a maximum of 0.5% (m/m). Specific Sulphur Emission Control Areas have been established where the emissions of sulphur are further restricted, such as the Channel, between France and the U.K. However, other pollutants such as Volatile Organic Compounds (VOC) or Particulate Matter (PM), are not regulated in terms of shipping emissions. VOCs are of particular importance in the atmospheric chemistry processes, especially because of their role in the formation of ozone and as precursors of secondary PM in the vicinity of densely populated coastal areas 4. This raises the question of which VOC are emitted by ships under these new emission standards, what their emission rates are and what their impact on air quality is? Only a few studies considered the speciation of VOC emitted by ships 5, yet those data are crucial for reliable gas-phase atmospheric chemistry modelling and correct impact assessment. Our study presents the analysis of a VOC dataset collected during an intensive one-month field campaign in the harbour of Dunkirk in northern France, the third largest French port. The observations were conducted on a site near ferry and cargo terminals and provided high temporal resolution measurements of VOCs, using a PTR-ToF-MS, alongside many other parameters (meteorology, particles, gases). Data analysis allowed the identification of more than 65 plumes from different ferries, based on a methodology that relies on favourable meteorological conditions, port office entries and tracers like SO2. Firstly, Emission Factors (EFs) have been calculated, providing an estimate of the relative amount of a pollutant emitted relative to CO2. For species like SO2 or CH4, our results were consistent with the EMEP emission inventory of 2021 (De Lauretis et al. 2021), however, some VOCs displayed large differences compared to ship exhaust determined EF within the EU/SCIPPER project 7. As an example, the median EF of benzene ions (C6H6.H+) was 27.87 mg/kg(fuel) versus 5.31 mg/kg(fuel) for SCIPPER, whereas toluene (C7H8.H+) was 23.37 mg/kg(fuel) versus 0.49 mg/kg(fuel) for exhaust measurement. Secondly, Positive Matrix Factorization has been applied to the dataset to investigate a shipping chemical profile of VOC that will allow us to calculate the contribution of shipping emission to the total VOC concentration in such harbour area. 1. Corbett, J. J. et al. Environ. Sci. Technol. 41, 8512–8518 (2007).2. Faber, J., Hanayama, S., Zhang, S. & Pereda, P. Fourth IMO GHG Study 2020 Executive-Summary. (2020).3. Merk, O. Shipping Emissions in Ports. vol. 2014/2 (2014).4. Fang, H. et al. Journal of Geophysical Research: Atmospheres 127, e2022JD037301 (2022).5. Xiao, Q. et al. Atmos. Chem. Phys. 18, 9527–9545 (2018).6. De Lauretis, R., Ntziachristos, L. & Trozzi, C. Air pollutant emission inventory guidebook 2019, update 2021. (2021).7. Timonen, H. et al. Ship on-board emissions characterisation. (2022).

The apportionment of equivalent black carbon (eBC) to combustion sources from liquid fuels (mainly fossil; eBC(LF)) and solid fuels (mainly non-fossil; eBC(SF)) is commonly performed using data from Aethalometer instruments (AE approach). This study evaluates the feasibility of using AE data to determine the absorption Angstrom exponents (AAEs) for liquid fuels (AAE(LF)) and solid fuels (AAE(SF)), which are fundamental parameters in the AE approach. AAEs were derived from Aethalometer data as the fit in a logarithmic space of the six absorption coefficients (470-950 nm) versus the corresponding wavelengths. The findings indicate that AAE(LF) can be robustly determined as the 1st percentile (PC1) of AAE values from fits with R-2 > 0.99. This R-2-filtering was necessary to remove extremely low and noisy-driven AAE values commonly observed under clean atmospheric conditions (i.e., low absorption coefficients). Conversely, AAE(SF) can be obtained from the 99th percentile (PC99) of unfiltered AAE values. To optimize the signal from solid fuel sources, winter data should be used to calculate PC99, whereas summer data should be employed for calculating PC1 to maximize the signal from liquid fuel sources. The derived PC1 (AAE(LF)) and PC99 (AAE(SF)) values ranged from 0.79 to 1.08, and 1.45 to 1.84, respectively. The AAE(SF) values were further compared with those constrained using the signal at mass-to-charge 60 (m/z 60), a tracer for fresh biomass combustion, measured using aerosol chemical speciation monitor (ACSM) and aerosol mass spectrometry (AMS) instruments deployed at 16 sites. Overall, the AAE(SF) values obtained from the two methods showed strong agreement, with a coefficient of determination (R-2) of 0.78. However, uncertainties in both approaches may vary due to site-specific sources, and in certain environments, such as traffic-dominated sites, neither approach may be fully applicable.

The uptake of glyoxal on realistic submicron mineral dust aerosol particles from a natural soil (Gobi Desert) is investigated during experiments in a large simulation chamber, under variable experimental conditions of relative humidity (RH), irradiation, and ozone concentrations. The uptake of glyoxal on the dust particles starts as soon as the glyoxal is injected into the chamber. At 80 % RH, the measured uptake coefficient of glyoxal on mineral dust is gamma = (9 +/- 5) x 10-3. The totality of the mass of reacting glyoxal is transformed into organic matter on the surface of the dust particles. The uptake of glyoxal is accompanied by the appearance of marker peaks in the organic mass spectra and a persistent growth in the volume concentration of the dust particles. While the mass of the organic matter on the dust rapidly reverts to values prior to uptake, the organic composition of the dust is modified irreversibly. Glycolic and other organic acids, but also oligomers, are detected on the dust. At 80 % RH, compounds ranging from C4 to C10 are observed as oligomerization products of glyoxal mono- and di-hydrate forms. The study suggests that dust aerosols could play a very substantial role in the formation of organic aerosols at high RH, but also that the reaction could have potentially important implications for the dust optical and hygroscopic properties, including their pH.

Semi-volatile organic compounds (SVOCs) exist in both gaseous and particulate phases in the atmosphere, and are important intermediate species for the formation of secondary organic aerosols. In this study, both phases of SVOCs are studied in the vicinity of Paris, France, and within São Paulo, Brazil aiming to better understand the coupling between anthropogenic and biogenic emissions in distinct urban settings. Both regions are representative of strong anthropogenic and biogenic sources of pollutants. These areas were within the scope of the ACROSS (Atmospheric Chemistry of the Suburban Forest) and BIOMASP+ (Biogenic emissions, chemistry, and impacts in the Metropolitan Area of São Paulo) projects, respectively. The ACROSS campaign took place from June to July 2022 and data analyzed here were acquired at the Rambouillet (RMB) forested site, about 50 km southwest of Paris. BIOMASP+ conducted intensive observations in April and May 2023, and data were collected at the Institute of Astronomy, Geophysics, and Atmospheric Sciences (Matão-IAG) urban site, within the University of São Paulo campus. Continuous measurements of ambient organics through a CHemical Analysis of aeRosols ON-line (CHARON) inlet coupled to a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) were carried out at both sites, as well as complementary variables such as aerosol chemical composition, regulated pollutants, and meteorological parameters, among others.The concentration of submicron bulk organic aerosol was comparable at both sites during ACROSS and BIOMASP+, reaching 5.0 µg/m3 and 7.3 µg/m3 for RMB and Matão-IAG, respectively. These are higher than typical 1-year averages observed at urban sites in Europe (3-4 µg/m3) [1] and previous observations near Matão-IAG in October 2012 (4.8 µg/m3) [2]. Biogenic VOCs showed distinct concentrations and temporal variabilities between sites with isoprene levels of 0.51 ppb vs 0.26 ppb of monoterpene in Brazil and Paris (0.35 ppb of isoprene vs 0.23 ppb of monoterpene) thus potentially leading to important differences in the subsequent secondary organic aerosol formation. Additionally, toluene, an anthropogenic marker, was higher at Matão-IAG (1.52 ppb) compared to RMB (0.25 ppb). This study will focus on SVOCs according to their mass spectra and temporal evolution and will compare the field observations to chamber experiments of biogenic and anthropogenic secondary organic aerosol formation. Those observations shall aid in understanding secondary formation processes and improve air quality modelling, as well as efficient pollution mitigation strategies in two contrasting large urbanized areas.Keywords: SVOC, Sao Paulo, Paris, SOA, CHARON-PTR-ToF-MSAcknowledgments: This work is funded and supported by Labex CaPPA, CPER ECRIN, ANR, and INSU LEFE-CHAT within the framework of BIOMASP and ACROSS projects. O. Murana’s field campaign in Brazil was supported by the Graduate Program “Science for a Changing Planet”, funded by the Program “Investissements d’avenir” (I-SITE ULNE / ANR-16-IDEX-0004 ULNE).References[1] Chen, G. et al., Environment International, vol. 166, p. 107325, 2022[2] Almeida, G. P. et al., Atmos. Chem. Phys., vol. 14, no. 14, pp. 7559-7572, 2014

Understanding the interaction of anthropogenic and biogenic emissions around large urban agglomerations remains an important question for atmospheric research and the key question of the ACROSS (Atmospheric Chemistry of the Suburban Forest) project. ACROSS is based on an intensive field campaign in the Paris area, including ground-based measurements in the urban inner centre and suburban and forested sites and measurements made on board aircraft, during the exceptionally hot and dry summer of 2022. In addition, 3D modelling represents an important tool in ACROSS, and here we use the available measurements from the campaign together with observations from air quality and meteorological networks to evaluate the WRF–CHIMERE model simulation for the ACROSS period. We find that the WRF model is able to reproduce the meteorological variability during the campaign, in particular during two heatwaves. The model reproduces the daily ozone maxima well but overestimates PM2.5 by a factor of 1.5–2, partly due to an overestimation of secondary aerosol, both organic and inorganic. For organic aerosol in the Île-de-France area, the biases are reduced to about ±20 %. These differences are in contrast with those of the existing literature and might have been increased by the hot conditions of summer 2022. For case studies during two heatwave days, the model shows the sources for two organic aerosol peaks above 20–30 µg m−3, on one occasion due to biogenic secondary organic aerosol formation in different forests around Paris and on another occasion due to the advection of wildfire aerosols in combination with secondary formation mainly from forest-emitted biogenic volatile organic compounds (BVOCs).

A summertime field campaign was conducted in Marseille, one of the major cruise and ferry ports in the Mediterranean, to provide comprehensive analysis of in-port ship emissions. High-temporal-resolution data were simultaneously collected from two monitoring stations deployed in the port area to examine the composition in both the gas and the particulate phases. More than 350 individual plumes were captured from a variety of ships and operational phases. Gaseous emissions are predominantly composed of NOx (86 %) and CO (12 %), with SO2 and CH4 each accounting for about 1 %. Although non-methane volatile organic compounds (NMVOCs) make up less than 0.1 % of the gaseous phase, they can be as high as 10 % under specific operational conditions. Submicron particles (PM1) are mainly composed of organics (75 %), black carbon (21 %), and sulfate (4 %) that is not balanced with ammonium. Among the ship-related characteristics investigated, the operational phase is the most influential, with a 3-fold increase in submicron particle (PM1) emissions, along with higher relative contributions of black carbon (BC) and sulfate and the detection of vanadium, nickel, and iron during manoeuvring/navigation compared to at berth. Pollutant levels in the port are higher than those found at the urban background site, with average concentrations of NOx, PM1, and particle numbers up to twice as high in the port. Analysis of the maximum concentrations reveals that pollutants such as SO2 and trace metals, including vanadium and nickel, are 2 to 10 times higher in the port area. This study provides robust support for enhancing source apportionment and emission inventories, both of which are crucial for assessing air, health, and climate impacts of shipping.

During the dry season, the Amazonian atmosphere is strongly impacted by fires, even in remote areas. However, there are still knowledge gaps regarding how each aerosol type affects the aerosol radiative forcing. This work characterizes the chemical composition of submicrometer aerosols and source apportionment of organic aerosols (OAs) and equivalent black carbon (eBC) to study their influence on light scattering and absorption at a remote site in central Amazonia during the dry season (August-December 2013). We applied positive matrix factorization (PMF) and multilinear regression (MLR) models to estimate chemical-dependent mass scattering efficiency (MSE) and extinction efficiency (MEE). Mean PM1 aerosol mass loading was 6.3 +/- 3.3 mu g m-3, with 77 % of organics, grouped into 3 factors: biomass burning OA (BBOA), isoprene-epoxydiol-derived secondary OA (IEPOX-SOA) and oxygenated OA (OOA). The bulk scattering and absorption coefficients at 637 nm were 17 +/- 10 and 3 +/- 2 Mm-1, yielding a single scattering albedo of 0.87 +/- 0.03. Although eBC represented only 6 % of the PM1 mass loading, MSE was highest for the eBC (13.58-7.62 m2 g-1 at 450-700 nm), followed by BBOA (7.96-3.10 m2 g-1) and ammonium sulfate (AS, 4.79-4.58 m2 g-1). The MEE was dominated by eBC (30.8 %), followed by OOA (19.9 %) and AS (17.6 %). The dominance of eBC over light scattering, in addition to absorption, plays a remarkably important role for this important climate agent, with potentially broad implications for more precise radiative forcing quantification, increasing climate modeling precision and representing deep contributions to Earth's climate system comprehension.

This paper presents a first comprehensive analysis of long-term measurements of atmospheric aerosol components from aerosol chemical speciation monitor (ACSM) and multiwavelength Aethalometer (AE33) instruments collected between 2015 and 2021 at 13 (sub)urban sites as part of the French CARA (Chemical Characterization of Particles) program. The datasets contain the mass concentrations of major chemical species within submicron aerosols (PM1), namely organic aerosols (OAs), nitrate (NO3-), ammonium (NH4+), sulfate (SO42-), non-sea-salt chloride (Cl-), and equivalent black carbon (eBC). Rigorous quality control, technical validation, and environmental evaluation processes were applied, adhering to both guidance from the French Reference Laboratory for Air Quality Monitoring (LCSQA) and the Aerosol, Clouds, and Trace Gases Research Infrastructure (ACTRIS) standard operating procedures. Key findings include geographical differences in the aerosol chemical composition, seasonal variations, and diel patterns, which are influenced by meteorological conditions, anthropogenic activities, and proximity to emission sources. Overall, OA dominates PM1 at each site (43 %-60 % of total mass), showing distinct seasonality with higher concentrations (i) in winter, due to enhanced residential heating emissions, and (ii) in summer, due to increased photochemistry favoring secondary aerosol formation. NO3 is the second most important contributor to PM1 (15 %-30 %), peaking in late winter and early spring, especially in northern France, and playing a significant role during pollution episodes. SO4 (8 %-14 %) and eBC (5 %-11 %) complement the major fine-aerosol species, with their relative contributions strongly influenced by the origin of air masses and the stability of meteorological conditions, respectively. A comparison with the 3D chemical transport model (CTM) CHIMERE shows high correlations between simulations and measurements, albeit with an OA concentration underestimation of 46 %-76 %. Regional discrepancies in NO3 concentration levels emphasize the importance of these datasets with respect to validating air quality models and tailoring air pollution mitigation strategies. The datasets can be found at 10.5281/zenodo.13318298 (Chebaicheb et al., 2024).

Criegee intermediates are reactive intermediates that are implicated in transforming the composition of Earth's troposphere and in the formation of secondary organic aerosol, impacting Earth's radiation balance, air quality and human health. Yet, direct identification of their signatures in the field remains elusive. Here, from particulate and gas-phase mass-spectrometric measurements in the Amazon rainforest, we identify sequences of masses consistent with the expected signatures of oligomerization of the CH2OO Criegee intermediate, a process implicated in ozonolysis-driven aerosol formation. We assess the potential contributions of oligomerization through laboratory ozonolysis experiments, direct kinetic studies of Criegee intermediate reactions, and high-level theoretical calculations. Global atmospheric models built on these kinetics results indicate that Criegee intermediate chemistry may play a larger role in altering the composition of Earth's troposphere than is captured in current atmospheric models, especially in areas of high humidity. However, the models still capture only a relatively small fraction of the observed signatures, suggesting considerable underestimates of Criegee intermediate concentrations and reactivity and/or the dominance of other, presently uncharacterized, oxidation mechanisms. Resolving the remaining uncertainties in emission inventories and the effects of atmospheric water vapour on key chemical reactions will be required to definitively assess the role of Criegee intermediate oligomerization reactions. Measurements of Criegee intermediate oligomerization signatures in the Amazon rainforest indicate that the role of Criegee intermediate chemistry in the composition of Earth's troposphere has been underestimated.

Aerosol mass balance studies based on filter samples require a conversion factor to derive organic matter (OM) concentrations from organic carbon (OC) measurements from thermo-optical methods. This factor provides indirect insights on the molecular structure of OM needed in chemical transport models. Site- and season-specific ratios of OC to OM (fOM:OC) were calculated using data from five rural background sites in France between 2012 and 2021 by relating the unidentified chemical fraction in PM2.5 samples to thermo-optical OC concentrations. Further, multiple linear formulations were used to evaluate the impact of possible artefacts on the determination of fOM:OC. The resulting fOM:OC was then compared to other estimates derived from online aerosol mass spectrometry data, showing good agreement. The spatial and temporal variability in fOM:OC is discussed considering factors such as seasonality, meteorological conditions and the atmospheric oxidative potential. Linear-mixed effect models were formulated to quantitatively determine the drivers which influence the fOM:OC at the French rural background sites. Both ozone and relative humidity were variables with statistically significant effects on fOM:OC, indicating that differences in the contributions from both photooxidation and water content, explain the variability in fOM:OC observed at the French rural background sites. Site-specific fOM:OC yielded more accurate PM2.5 mass closure and are therefore recommended in mass-balance exercises. Accurate fOM:OC are critical to maintain consistency in OM time series, especially in cases where filter-based time series may be replaced by state-of-the-art online instrumentation.

Fine particulate matter (PM2.5) was monitored at five rural background locations in France from 2012 to 2021. Annual PM2.5 ranged from 5 to 15 mu g m(-3), all sites repeatedly exceeding the 2021 annual World Health Organization guideline. Chemical speciation including organic and elemental carbon (OC, EC), secondary inorganic aerosols (SIA: NO3-, SO42-, NH4+) and other major water-soluble ions (Cl-, Na+, Mg2+, Ca2+, K+) were monitored on 24-h filters covering 14% of the year. A source apportionment of OM was undertaken based on fine potassium and using representative ratios for domestic biomass burning (BB) and fossil fuel (FF) emissions. The latter dominated the EC fraction (55-60%) while BB was the main primary source of OM (27-54%). The average mass balance of PM2.5 at the French rural background atmospheric sites was: secondary organic aerosol (18-35%), BB (17-27%), non-sea-salt sulphate (12-17%), nitrate (6-22%), ammonium (7-11%), FF (4-6%), mineral dust (3-9%) and sea salt (1-2%). Secondary aerosols were the main component of PM2.5 through all seasons, with SIA dominating in spring episodes. The contribution of OM to PM2.5 was larger at the southern sites whereas the contribution of SIA was larger at the northern sites. The mean OC/EC ratio and the good correlations between OC, EC, and fine potassium suggested that BB was the main primary source contributing to carbonaceous aerosols, 27-54% to total OM depending on the site; and also, to PM2.5 (17-27%). Stronger regulations of OM sources including BB, nitrate from combustion, and ammonium from agricultural sources are needed to reduce PM2.5 at rural background sites on an annual and episodic basis, respectively.

Understanding the lifecycle of light-absorbing carbonaceous aerosols, from emission to deposition, is critical for assessing their climate impact. This study integrated multi-year aerosol observations from the ATOLL (ATmospheric Observations in liLLe, northern France) platform, with air mass back trajectories and emission inventory as a newly developed “INTERPLAY” (IN-siTu obsERvations, hysPLit, And emission inventorY) approach. Applied to black carbon (BC), the method apportioned source contributions (shipping, vehicular, residential heating, industrial) and studied aerosol aging effects, notably on the brown carbon (BrC) component. Results estimate that, throughout the year, vehicular traffic dominated BC (31 %), followed by shipping (25 %, of which one-third was from canals/rivers) and residential heating (21 %). Comparing INTERPLAY results with the aethalometer model highlights that the “residential sector” BC can be entirely apportioned to BC from wood burning (BCwb), notably in winter, while vehicular traffic corresponds to only about 41 % of BC fossil fuel (BCff) at the ATOLL site, the rest being apportioned to shipping (33 %) and industrial (23 %) emissions. Thus, vehicular traffic and BCff should not be used interchangeably, particularly in regions near intense maritime traffic. Concerning BrC, our analysis confirms a dominant role of residential heating. Focusing on winter, results suggest a considerable decrease in the BrC component only 24 h after emission, with fresh residential emissions being responsible for 72 % of BrC absorption at ATOLL. The results from this study allow for an improved understanding of sources and atmospheric dynamics of light-absorbing carbonaceous aerosols in northern France, being crucial for both source abatement strategies as well as a better assessment of their climate impact.

Abstract. This paper presents a first comprehensive analysis of long-term measurements of atmospheric aerosol components from Aerosol Chemical Speciation Monitor (ACSM) and multi-wavelength Aethalometer (AE33) instruments collected between 2015 and 2021 at 13 (sub)urban sites as part of the French CARA program. The datasets contain the mass concentrations of major chemical species within PM1, namely organic aerosols (OA), nitrate (NO3-), ammonium (NH4+), sulfate (SO42-), non-sea-salt chloride (Cl-), and equivalent black carbon (eBC). Rigorous quality control, technical validation, and environmental evaluation processes were applied, adhering to both the guidance from the French reference laboratory for air quality monitoring and the Aerosol, Clouds, and Trace gases Research Infrastructure (ACTRIS) standard operating procedures. Key findings include geographical differences in aerosol chemical composition, seasonal variations, and diel patterns, which are influenced by meteorological conditions, anthropogenic activities, and proximity to emission sources. Overall, OA dominates PM1 at each site (43–60 %), showing distinct seasonality with higher concentrations (i) in winter, due to enhanced residential heating emissions, and (ii) in summer, due to increased photochemistry favoring secondary aerosol formation. NO3 is the second most important contributor to PM1 (15–30 %), peaking in late winter and early spring, especially in northern France, and playing a significant role during pollution episodes. SO4 (8–14 %) and eBC (5–11 %) complement the major fine aerosol species, with their relative contributions strongly influenced by the origin of air masses and the stability of meteorological conditions, respectively. Such chemically-speciated multi-year datasets have significant value for the scientific community, offering opportunities for future research, including source apportionment studies, trend analyses, and epidemiological investigations. They are also vital for evaluating and validating regional air quality models. In this regard, a comparison with the CHIMERE Chemical Transport Model shows high correlations between simulations and measurements, albeit underestimating OA concentrations by 46–76 %. Regional discrepancies in NO3 concentration levels emphasize the importance of these datasets in validating air quality models and tailoring air pollution mitigation strategies.