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Open research questions in Atmospheric chemistry and aerosols

135 unresolved questions extracted from the limitations and future-work sections of 616 Atmospheric chemistry and aerosols papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • We developed and characterized a five-channel TD-CEAS system for in situ measurements of NO2 and operationally defined ON classes in both the gas and particle phases. The instrument couples a single NO2 detector (405 nm) with two thermal dissociation setpoints (250 and 450 °C) and paired inlet/outlet configurations (upstream filtration for gas-only; downstream filtration for particle-inclusive sampling) to enable retrieval of gas- and particle-phase (cid:54)PNs and (cid:54)ANs by Figure 9. Daily average of (a) temperature and relative humidity, (b) gas- and particle-phase (cid:54)PNs, and (c) gas- and particle-phase (cid:54)ANs. Shading indicating the error of ±1σ. comparison of raw (cid:54)PNs and PAN (where g(cid:54)PNs are, at certain times, unreasonably lower than PAN), it is necessary https://doi.org/10.5194/amt-19-4797-2026 Atmos. Meas. Tech., 19, 4797–4813, 2026 4810 X. Tian et al.: Five-channel TD-CEAS with NO/NO2 interference correction under high-NOx conditions channel differencing. In the field configuration used here, the system cycles through the five channels plus an N2 reference segment, providing a complete set of NO2, g/p(cid:54)PNs, and g/p(cid:54)ANs at a 6 min cadence. Laboratory characterization of PNs and ANs standards supported the selection of operational TD temperatures. Under these conditions, particulate inorganic nitrate (NaNO3) showed minimal contribution to the NO2 signal at 450 °C. Allan deviation analysis yielded 1 σ (1 s) detection limits of 49 pptv for g(cid:54)PNs, 49 pptv for p(cid:54)PNs, 48 pptv for g(cid:54)ANs, and 68 pptv for p(cid:54)ANs. The gas-phase (cid:54)PN response was validated using PAN, with TD-CEAS PAN-equivalent mixing ratios agreeing with GC-ECD measurements (slope = 0.987; R2 = 0.988). For particle-phase (cid:54)ANs, an operational calibration based on filter thermolysis of 2-EHN produced a linear response (slope = 1.036 ± 0.028) and a method detection limit of 0.029 µg NO2. Dedicated interference experiments demonstrated that NO and NO2 can introduce substantial, nonlinear biases in (cid:54)PNs retrievals through radical chemistry in the TD inlet. These effects are reduced using a regression-based correction model that outperformed the reproduced lookuptable approach across the tested NOx conditions. Field deployment at an urban site in Guangzhou during September–October 2025 demonstrated stable instrument operation under high-NOx conditions and produced continuous time series of gas- and particle-phase ON classes. During the October intensive period, corrected g(cid:54)PNs covaried well with independently measured PAN, with R2 of 0.83, and PAN accounted for approximately 78 % of daytime g(cid:54)PNs. The observed diurnal variation of gas-phase ONs and the day-night pattern of particle-phase ONs provide a useful approach for investigating the daytime phase partitioning of ONs and the transformation processes of reactive nitrogen in urban air.

    Five-channel TD-CEAS measurements of gaseous and particulate organic nitrates with NO ∕ NO <sub>2</sub> interference correction under high-NO <sub> <i>x</i> </sub> conditions · 2026 · DOI

  • Here we present an Analysis that links droplet-generation methods to operative boundary conditions, separates detection from net H2O2 production and interfacial attribution through an evidence ladder, and distils a controlled-variable checklist for experiments designed to resolve apparently conflicting results across studies.

    Evidencing microdroplet H2O2 redox chemistry: from detection to mechanistic attribution · 2026 · DOI

  • Ammonia (NH3) plays a crucial role in the complex physicochemical processes occurring in the atmosphere, but the mechanisms governing secondary organic aerosol (SOA) formation from NH3-involved interactions between mixed anthropogenic and biogenic organic compounds remain poorly understood, thereby limiting the predictive capacity for air quality and climate.

    Investigating the role of ammonia in enhancing secondary organic aerosol formation from the co-photooxidation of anthropogenic and biogenic VOCs · 2026 · DOI

  • Their transformation is closely coupled with aqueous S(IV) oxidation, jointly driving the formation of sulfate and organosulfates; however, the underlying mechanisms remain poorly understood.

    Rapid secondary organic aerosol formation at the air–water interface from methoxyphenols in wildfire emissions: UVA-driven S(IV) photooxidation to organosulfates · 2026 · DOI

  • China’s Clean Air Action (CAA) plan implemented since 2013 has significantly altered atmospheric composition, and yet its impact on the terrestrial carbon sink remains unclear.

    Dissimilar roles of aerosols, nitrogen deposition and ozone on the terrestrial carbon sink in China during 2010–2020 · 2026 · DOI

  • The mechanism predicts that further oxidation of third-generation products may yield compounds with sufficiently low volatility to nucleate new aerosol particles; direct chamber or smog chamber experiments measuring new particle formation rates and growth kinetics from these predicted ultra-low volatility organic compounds (ULVOCs) have not been conducted.

    Mechanistic investigations of the formation of multifunctional products from the multi-generation ●OH oxidation of styrene · 2026 · DOI

  • Bicyclic peroxide radical (BPR) formation and subsequent reactions with HO2 and NO are proposed as pathways to second-generation products; experimental confirmation of BPR intermediates through spectroscopic detection (e.g., infrared, mass spectrometry) or indirect characterization methods is currently unavailable.

    Mechanistic investigations of the formation of multifunctional products from the multi-generation ●OH oxidation of styrene · 2026 · DOI

  • The dominant ortho-site OH-addition pathway for second generation oxidation of 1st-ROOH and 1st-RONO2 is reported to be consistent with analogous systems (toluene, phenol); however, direct comparative kinetic measurements quantifying the regioselectivity differences between these aromatic precursors under identical conditions are absent.

    Mechanistic investigations of the formation of multifunctional products from the multi-generation ●OH oxidation of styrene · 2026 · DOI

  • The fractional yields for second and third generation closed-shell products vary significantly (e.g., S26: 4.8%, S47: 26.3%, S62: 0.03%); systematic sensitivity analysis examining how experimental conditions (temperature, pressure, NOx concentration, humidity) affect these yield distributions has not been performed.

    Mechanistic investigations of the formation of multifunctional products from the multi-generation ●OH oxidation of styrene · 2026 · DOI

  • The volatility predictions for third-generation closed-shell products (S47, S51, S58, S62) rely on SIMPOL.1 estimation methods; direct experimental measurements of saturation vapor pressure and condensation behavior of these highly oxygenated and nitrogenated compounds under atmospheric conditions are needed to validate particle formation potential.

    Mechanistic investigations of the formation of multifunctional products from the multi-generation ●OH oxidation of styrene · 2026 · DOI

  • The intramolecular H-shift rate coefficient (kMC-TST = 1.6 × 10−4 s−1) for first generation RO2 radicals in styrene OH oxidation was calculated theoretically; experimental validation of this rate through direct measurement or indirect kinetic studies in controlled atmospheric conditions is lacking.

    Mechanistic investigations of the formation of multifunctional products from the multi-generation ●OH oxidation of styrene · 2026 · DOI

  • The structures of some specific multi-generation oxidation products of styrene remain uncharacterized in laboratory chamber experiments and are merely inferred from exact mass and fragmentation data rather than definitively identified through experimental spectroscopic techniques.

    Mechanistic investigations of the formation of multifunctional products from the multi-generation ●OH oxidation of styrene · 2026 · DOI

  • The relationship between glyoxal formation yields from isoprene oxidation and formaldehyde production in atmospheric models needs validation using aircraft observations (e.g., ATom, SENEX campaigns) under varying atmospheric conditions, particularly in the remote free troposphere where OH radical concentrations differ significantly from continental boundary layer regions.

    Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity · 2026 · DOI

  • The contribution of marine isoprene emissions from seaweeds and phytoplankton to the global glyoxal budget remains poorly quantified; measurements of isoprene and glyoxal concentrations in coastal regions with varying biological activity and detailed process-based parameterizations for open ocean emissions are needed.

    Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity · 2026 · DOI

  • The long-range transport mechanisms for glyoxal and formaldehyde observed from satellite data during the 2018 Canadian wildfires require 3D chemical transport model simulations to quantify vertical mixing, wet/dry deposition losses, and secondary production along transport pathways to improve understanding of glyoxal persistence at continental scales.

    Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity · 2026 · DOI

  • Wildfire emission factors for glyoxal precursors (non-methane organic gases, isoprene, biogenic VOCs) show high uncertainty across different fire types and vegetation regimes; systematic measurements during controlled burns and field campaigns are needed to constrain emissions from tropical peatlands, boreal forests, and savanna fires.

    Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity · 2026 · DOI

  • Atmospheric oxidation chemistry models require updated compact mechanisms for aromatic precursor oxidation pathways that produce glyoxal, with specific focus on benzene, toluene, and xylene degradation under varying NOx regimes to improve predictions of glyoxal concentrations in urban and industrial regions.

    Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity · 2026 · DOI

  • The Henry's law constants for glyoxal and its precursors (formaldehyde, isoprene oxidation products) need refinement across different temperature and salinity regimes relevant to marine boundary layer conditions, as current values may not accurately represent air-sea partitioning in tropical and polar regions.

    Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity · 2026 · DOI

  • The glyoxal retrieval algorithms from OMI and Sentinel-5P satellite measurements require validation against ground-based and aircraft measurements across diverse atmospheric conditions, particularly in regions with high aerosol loading and varying surface albedo where satellite retrievals may be compromised.

    Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity · 2026 · DOI

  • Chamber studies of biogenic secondary organic aerosol aging via OH radical reactions (Donahue et al., 2012) have been conducted, but the quantitative relationship between aging timescales in laboratory chambers (typically hours) and atmospheric aging pathways involving aerosol-phase reactions and heterogeneous uptake over days-to-weeks remains unconstrained for integration into regional and global chemical transport models.

    Atmospheric Simulation Chambers in the ACTRIS Research Infrastructure · 2026 · DOI

  • Water vapor measurement techniques were intercompared in AquaVIT-1 (Fahey et al., 2014), but equivalent systematic intercomparison exercises for humidity measurement accuracy and performance across the ACTRIS atmospheric simulation chamber network—which require humidified aerosol experiments under controlled conditions—have not been documented.

    Atmospheric Simulation Chambers in the ACTRIS Research Infrastructure · 2026 · DOI

  • Brown carbon formation pathways through multiphase photochemical reactions (glyoxal, catechole, guaiacol oxidation) have been studied individually in chambers, but the interactive effects of concurrent iron-catalyzed and photochemical browning mechanisms under realistic atmospheric conditions—particularly varying iron speciation and solubility—have not been systematically characterized in atmospheric simulation chambers.

    Atmospheric Simulation Chambers in the ACTRIS Research Infrastructure · 2026 · DOI

  • Multiple studies document secondary organic aerosol formation from α-pinene ozonolysis in atmospheric chambers, but direct systematic comparison of hygroscopicity and optical properties across different chamber designs, wall materials, and operating conditions (humidity, temperature, residence time) is lacking, preventing chamber-independent validated datasets for climate modeling.

    Atmospheric Simulation Chambers in the ACTRIS Research Infrastructure · 2026 · DOI

  • The intercomparison of NO3 radical detection instruments in the SAPHIR atmospheric simulation chamber (Dorn et al., 2013) provides instrumental validation, but systematic comparison of detection techniques across different chamber facilities (SAPHIR, EUPHORE, PSI, etc.) under identical chemical conditions remains absent, limiting standardization of nitrate radical measurement protocols in atmospheric simulation chambers.

    Atmospheric Simulation Chambers in the ACTRIS Research Infrastructure · 2026 · DOI

  • The paper does not quantify how the choice between OTD/LIS lightning NOx parameterization and alternative lightning algorithms affects the sensitivity study conclusions about isoprene-NOx interactions in GEOS-Chem at 2° × 2.5° resolution.

    Inferring drivers of tropical isoprene: competing effects of emissions and chemistry · 2026 · DOI

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135 open questions have been extracted from the limitations and future-work passages of 616 Atmospheric chemistry and aerosols papers in our library. Each one below links back to the study that raised it, so you can read the original claim in context.

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