Changes in engine technologies and after-treatment devices can profoundly alter the chemical composition of the emitted pollutants. To investigate these effects, we characterized the emitted particles' chemical composition of three diesel and four gasoline Euro 5 light-duty vehicles tested at a chassis dynamometer facility. The dominant emitted species was black carbon (BC) with emission factors (EFs) varying from 0.2 to 7.1 mg km⁻¹ for direct-injection gasoline (GDI) vehicles, from 0.02 to 0.14 mg km⁻¹ for port fuel injection (PFI) vehicles, and 0.003 to 0.9 mg km⁻¹ for diesel vehicles. The organic matter (OM) EFs varied from 5 to 103 µg km⁻¹ for GDI gasoline vehicles, from 1 to 8 µg km⁻¹ for PFI vehicles, and between 0.15 and 65 µg km⁻¹ for the diesel vehicles. The first minutes of cold-start cycles contributed the largest PM fraction including BC, OM, and polycyclic aromatic hydrocarbons (PAHs). Using a high-resolution time-of-flight mass spectrometer (HR-ToF-AMS), we identified more than 40 PAHs in both diesel and gasoline exhaust particles including methylated, nitro, oxygenated, and amino PAHs. Particle-bound PAHs were 4 times higher for GDI than for PFI vehicles. For two of the three diesel vehicles the PAH emissions were below the detection limit, but for one, which presented an after-treatment device failure, the average PAHs EF was 2.04 µg km⁻¹, similar to the GDI vehicle's values. During the passive regeneration of the catalysed diesel particulate filter (CDPF) vehicle, we measured particles of diameter around 15 nm mainly composed of ammonium bisulfate. Transmission electron microscopy (TEM) images revealed the presence of ubiquitous metal inclusions in soot particles emitted by the diesel vehicle equipped with a fuel-borne-catalyst diesel particulate filter (FBC-DPF). X-ray photoelectron spectroscopy (XPS) analysis of the particles emitted by the PFI vehicle showed the presence of metallic elements and a disordered soot surface with defects that could have consequences on both chemical reactivity and particle toxicity. Our findings show that different after-treatment technologies have an important effect on the emitted particles' levels and their chemical composition. In addition, this work highlights the importance of particle filter devices' condition and performance.

In order to gain understanding on the vertical structure of atmospheric water vapour above mountain lakes and to assess its link with the isotopic composition of the lake water and with small-scale dynamics (i.e. valley winds, thermal convection above complex terrain), the L-WAIVE (Lacustrine-Water vApor Isotope inVentory Experiment) field campaign was conducted in the Annecy valley in the French Alps during 10 d in June 2019. This field campaign was based on an original experimental synergy between a suite of ground-based, boat-borne, and two ultra-light aircraft (ULA) measuring platforms implemented to characterize the thermodynamic and isotopic composition above and in the lake. A cavity ring-down spectrometer and an in-cloud liquid water collector were deployed aboard one of the ULA to characterize the vertical distribution of the main stable water isotopes (H${}_{\mathrm{2}}^{\mathrm{16}}$ O, H${}_{\mathrm{2}}^{\mathrm{18}}$ O and H²H¹⁶O) both in the air and in shallow cumulus clouds. The temporal evolution of the meteorological structures of the low troposphere was derived from an airborne Rayleigh–Mie lidar (embarked on a second ULA), a ground-based Raman lidar, and a wind lidar. ULA flight patterns were repeated several times per day to capture the diurnal evolution as well as the variability associated with the different weather events encountered during the field campaign, which influenced the humidity field, cloud conditions, and slope wind regimes in the valley. In parallel, throughout the campaign, liquid water samples of rain, at the air–lake water interface, and at 2 m depth in the lake were taken. A significant variability of the isotopic composition was observed along time, depending on weather conditions, linked to the transition from the valley boundary layer towards the free troposphere, the valley wind intensity, and the vertical thermal stability. Thus, significant gradients of isotopic content have been revealed at the transition to the free troposphere, at altitudes between 2.5 and 3.5 km. The influence of the lake on the atmosphere isotopic composition is difficult to isolate from other contributions, especially in the presence of thermal instabilities and valley winds. Nevertheless, such an effect appears to be detectable in a layer of about 300 m thickness above the lake in light wind conditions. We also noted similar isotopic compositions in cloud drops and rainwater.

Source apportionment models were widely used to successfully assign highly time-resolved aerosol data to specific emissions and/or atmospheric chemical processes. These techniques are necessary for targeting the sources affecting air quality and for designing effective mitigation strategies. Moreover, evaluation of the toxicity of airborne particulate matter is important since the classically measured particulate matter (PM) concentrations appear insufficient for characterizing the impact on human health. Oxidative potential (OP) measurement has recently been developed to quantify the capability of PM to induce an oxidative imbalance in the lungs. As a result, this measurement unit could be a better proxy than PM mass concentration to represent PM toxicity. In the present study, two source apportionment analyses were performed using positive matrix factorization (PMF) from organic aerosol (OA) mass spectra measured at a 15 min time resolution using a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) and from 19 trace elements measured on an hourly basis using an online metal analyser (Xact 625i). The field measurements were carried out in summer 2018. While it is common to perform PMF studies individually on ACSMs and more recently on Xact datasets, here we used a two-step methodology leading to a complete PM₁ source apportionment. The outputs from both OA PMF and Xact PMF, the inorganic species concentrations from the ACSM, and the black carbon (BC) fractions (fossil fuel and wood burning) measured using an Aethalometer (AE33) were gathered into a single dataset and subjected to a combined PMF analysis. Overall, eight factors were identified, each of them corresponding to a more precise source than performing single PMF analyses. The results show that besides the high contribution of secondary ammonium sulfate (28 %) and organic nitrate (19 %), about 50 % of PM₁ originated from distinct combustion sources, including emissions from traffic, shipping, industrial activities, cooking, and biomass burning. Simultaneously, PM₁ filters were collected during the experimental period on a 4 h sampling basis. On these filters, two acellular OP assays were performed (dithiothreitol; OP^DTT and ascorbic acid; OP^AA) and an inversion method was applied on factors issued from all PMFs to assess the contribution of the PM sources to the OP. This work highlights the sensitivity of OP^AA to industrial and dust resuspension sources and those of OP^DTT to secondary ammonium sulfate, shipping, and biomass burning.

Organic nitrates (RONO₂) are secondary compounds whose fate is closely related to the transport and removal of NO_x in the atmosphere. Despite their ubiquitous presence in submicron aerosols, the photochemistry of RONO₂ has only been investigated in the gas phase, leaving their reactivity in condensed phases poorly explored. This work aims to address this gap by investigating, for the first time, the reaction products and the mechanisms of aqueous-phase photolysis of four RONO₂ (i.e., isopropyl nitrate, isobutyl nitrate, α-nitrooxy acetone, and 1-nitrooxy-2-propanol). The results show that the reactivity of RONO₂ in the aqueous phase differs significantly from that in the gas phase. In contrast to the gas phase, where RONO₂ release NO_x upon photolysis, the aqueous-phase photolysis of RONO₂ leads primarily to the direct formation of nitrous acid (HONO or HNO₂), which was confirmed by quantum chemistry calculations. Hence, the aqueous-phase photolysis of RONO₂ represents both a NO_x sink and a source of atmospheric nitrous acid, a significant precursor of ⋅ OH and ⋅ NO. These secondary radicals (⋅ OH and ⋅ NO) are efficiently trapped in the aqueous phase, leading to the formation of HNO₃ and functionalized RONO₂. This reactivity can thus potentially contribute to the aging of secondary organic aerosol (SOA) and serves as an additional source of aqueous-phase SOA.

In this paper, we focus on airborne hyperspectral imaging methodology to characterize particulate matter (PM) near industrial emission sources. Two short-term intensive campaigns were carried out in the vicinity of a refinery in the south of France, in September 2015 and February 2016. Different protocols of in situ PM measurements were performed, at stack measurements (flow rate and offline chemical analysis) and online measurement at the refinery border (size distribution, concentration, and chemistry of aerosols). A multitemporal methodology to retrieve aerosol type, to map the aerosol concentration, and to quantify mass flow rate from airborne hyperspectral data is described in this paper. This method applied to the refinery detected plume from the main stack yields a black carbon to sulfate ratio of 10/90 in mass inside the plume, with an average size distribution smaller than 100 nm. These results are in a good agreement with the online analysis of aerosols at the refinery border. The resulting quantitative map with a metric spatial resolution leads to an estimated flow rate of about 1 g/s and is in a good agreement with in situ stack measurements and modeling.