Liyuan Zhou

Marine primary organic aerosols (mPOAs) play a key role in ocean–atmosphere–climate interactions. Yet their effects on cloud formation remain uncertain because mPOA number size distribution measurements are lacking, obscuring its parameterizations for climate models. The mPOA number size distribution is resolved by combining long-term hygroscopicity, size, number and composition measurements in pristine marine air. The resulting bimodal distribution shows strong Aitken (∼60 nm) and accumulation (∼150 nm) modes, unlike the parameterization in widely used models. Total mPOA number is probably underestimated by a factor of three (observed/parameterized ≈ 3.1), doubling mPOA-originated cloud condensation nuclei across realistic marine supersaturations. An observation-guided sensitivity analysis indicates a potential first aerosol indirect effect of –0.03 to –0.04 W/m2 over the global ocean, reaching –0.1 to –0.2 W/m2 over biologically active waters when mPOA surface tension reduction is considered, underscoring the need for trustworthy mPOA representation to reduce the uncertainties in aerosol–cloud interactions.

Organosulfates (OSs) are important components of secondary organic aerosol, yet their molecular composition and formation processes in mountain atmospheres remain poorly constrained. In this study, PM2.5 samples collected during summer and winter at a high-altitude background site at Wuyi Mountain, southeastern China, were analyzed using high-performance liquid chromatography coupled with orbitrap mass spectrometry (HPLC-Orbitrap MS) to examine how seasonal changes in precursor availability and atmospheric processing influence OS molecular composition. Clear seasonal differences were observed in the molecular composition and structural characteristics. Summer OSs were enriched in more highly oxygenated species (with OSc >-1 accounting for 72 % of the total OS signal abundance), whereas winter OSs were characterized by larger (C5–C23), less oxygenated (O4–O7), and more unsaturated molecules, reflecting more diverse precursor influences. Among 35 structurally identified OSs, isoprene- and monoterpene-derived species were enriched in summer, while aliphatic-like OSs and monoterpene-derived nitrooxy-OSs were more abundant in winter, indicating seasonal variations in precursor availability and the relative importance of atmospheric processing. Mechanistic analysis suggested that summer OS formation was more closely associated with sulfate-rich and highly acidic conditions favorable for multiphase processing, whereas wintertime OS formation reflected greater influences from elevated atmospheric oxidants and nitrogen-related chemistry. Regional transport further contributed to wintertime OS composition by increasing anthropogenic precursor inputs and promoting atmospheric aging. These findings demonstrate that seasonal OS variability in mountain environments reflects the interplay between precursor availability and atmospheric processing, providing field-based molecular evidence for the coupling of biogenic and anthropogenic influences in secondary organic aerosol formation and evolution.

Arabian incense (Bakhoor) burning is a widely practiced fragrancing and ceremonial activity, yet how the Bakhoor composition controls particle emissions and oxidative potential remains poorly constrained, especially under repeated use in low-ventilation settings. Here we characterized emissions from Bakhoor burning in a controlled chamber using a charcoal-assisted heating configuration representative of common practice and quantified aerosol oxidative potential using complementary acellular dithiothreitol (DTT) activity and a macrophage-based intracellular oxidative-stress response, with smoldering sidestream cigarette smoke as a protocol-matched indoor combustion reference. Normalized by the initial Bakhoor mass per burn, Bakhoor burning produced particle mass and number emission rates of 670–1690 µg min ⁻¹ g ⁻¹ and (6–7) × 10 ¹¹ particles min ⁻¹ g ⁻¹ , respectively. Ultrafine particles contributed 70 %–75 % of the total particle number, and their emission rates substantially exceeded those from sidestream cigarette smoke. Across Bakhoor materials, emission magnitude followed a nonlinear power-law relationship with the loading of the hexane-soluble fraction, indicating that this fraction is an important control on particle production. In the acellular assay, the water-soluble particle mass-normalized DTT consumption rate (OPDTT, mWS) was approximately 32 pmol min ⁻¹ µg ⁻¹ , modestly lower than that of cigarette smoke particles, whereas Bakhoor burning particles elicited stronger intracellular oxidative-stress responses. Ozone aging increased oxidative potential for both sources, and the acellular and cellular responses remained evident after aging equivalent to days of indoor exposure. Overall, Bakhoor burning represents a previously underrecognized source of ultrafine aerosol with substantial oxidative potential.

Arabian incense (Bakhoor) burning is a widely practiced fragrancing and ceremonial activity, yet how the Bakhoor composition controls particle emissions and oxidative potential remains poorly constrained, especially under repeated use in low-ventilation settings. Here we characterized emissions from Bakhoor burning in a controlled chamber using a charcoal-assisted heating configuration representative of common practice and quantified aerosol oxidative potential using complementary acellular dithiothreitol (DTT) activity and a macrophage-based intracellular oxidative-stress response, with smoldering sidestream cigarette smoke as a benchmark source. Normalized by the initial Bakhoor mass per burn, Bakhoor burning produced particle mass and number emission rates of 670–1690 µg min^-1 g^-1 and (6–7) × 10¹¹ particles min^-1 g^-1, respectively. Ultrafine particles contributed 70–75 % of the total particle number, and their emission rates substantially exceeded those from sidestream cigarette smoke. Across Bakhoor materials, emission magnitude followed a nonlinear power-law relationship with the loading of the hexane-soluble fraction, indicating that this fraction is an important control on particle production. In the acellular assay, the particle mass-normalized DTT consumption rate (OP_DTTm) was approximately 32 pmol min^-1 µg^-1, modestly lower than that of cigarette smoke particles, whereas Bakhoor burning particles elicited stronger intracellular oxidative-stress responses. Ozone aging increased oxidative potential for both sources, and the acellular and cellular responses remained evident after aging equivalent to days of indoor exposure. Overall, Bakhoor burning represents a previously underrecognized source of ultrafine aerosol with substantial oxidative potential.

Arabian incense (Bakhoor) burning is a widely practiced fragrancing and ceremonial activity, yet how the Bakhoor composition controls particle emissions and oxidative potential remains poorly constrained, especially under repeated use in low-ventilation settings. Here we characterized emissions from Bakhoor burning in a controlled chamber using a charcoal-assisted heating configuration representative of common practice and quantified aerosol oxidative potential using complementary acellular dithiothreitol (DTT) activity and a macrophage-based intracellular oxidative-stress response, with smoldering sidestream cigarette smoke as a benchmark source. Normalized by the initial Bakhoor mass per burn, Bakhoor burning produced particle mass and number emission rates of 670–1690 µg min^-1 g^-1 and (6–7) × 10¹¹ particles min^-1 g^-1, respectively. Ultrafine particles contributed 70–75 % of the total particle number, and their emission rates substantially exceeded those from sidestream cigarette smoke. Across Bakhoor materials, emission magnitude followed a nonlinear power-law relationship with the loading of the hexane-soluble fraction, indicating that this fraction is an important control on particle production. In the acellular assay, the particle mass-normalized DTT consumption rate (OP_DTTm) was approximately 32 pmol min^-1 µg^-1, modestly lower than that of cigarette smoke particles, whereas Bakhoor burning particles elicited stronger intracellular oxidative-stress responses. Ozone aging increased oxidative potential for both sources, and the acellular and cellular responses remained evident after aging equivalent to days of indoor exposure. Overall, Bakhoor burning represents a previously underrecognized source of ultrafine aerosol with substantial oxidative potential.

Secondary organic aerosol (SOA) formation is strongly influenced by relative humidity (RH), yet the underlying processes remain insufficiently understood under realistic atmospheric conditions. This study investigates RH-dependent SOA formation from ambient urban air using a field-deployable oxidation flow reactor (OFR), focusing on the multigenerational oxidation of volatile organic compound (VOC) precursors and their gas-to-particle transformation. Elevated RH markedly enhanced SOA production, yielding nearly 5-fold higher OA mass growth compared to low-RH oxidation under comparable photochemical ages. Evolution patterns of oxygenated VOCs (OVOCs) reveal that high RH accelerates the oxidative transformation of less-oxidized, higher-volatility intermediates into more-oxidized, lower-volatility products. These generational products facilitate SOA formation via condensation onto pre-existing particles and through formation and growth of new particles. This is corroborated by the more pronounced increase in particle number concentrations at 20-200 nm during high-RH oxidation, alongside substantial OA mass growth in both newly formed particles (100-200 nm) and pre-existing particles (∼500 nm). Potential water photolysis and thus OH production within the particle phase under high RH may also contribute to the oxidation processes. Overall, this work highlights the multifaceted role of RH in urban SOA formation, reflecting its concurrent influences on OVOC transformation, particle formation and growth, and gas-particle partitioning of oxidized products. These insights refine our understanding of SOA formation mechanisms under realistic atmospheric conditions.

Molecular-level characterization of organic aerosol (OA) is critical for understanding its sources and atmospheric evolution, yet remains analytically challenging due to its broad volatility distribution and complex chemical composition. In this study, we develop a dual-mode solid-phase microextraction (DM-SPME) approach coupled with gas chromatography-orbitrap mass spectrometry (GC-Orbitrap MS) that enables direct, high-sensitivity detection of OA in complex ambient samples. By integrating headspace and direct immersion extraction, DM-SPME improves the detection of higher-volatility compounds and expands the accessible volatility range, spanning pure saturation mass concentration from 10^–4 to 10⁶ μg m^–3. Application to particulate samples from pristine marine and forest air to polluted urban air through nontargeted analysis shows that DM-SPME detects ∼50% more compounds and ∼40% higher measured concentrations than conventional solvent extraction, with pronounced enhancement for polycyclic aromatic hydrocarbons, ketones, aldehydes, and aliphatic hydrocarbons. Despite these differences, intersite variability in OA numbers and concentrations was consistently captured by both methods, supporting the robustness of DM-SPME for comparative analysis. Volatility-oxidation analysis further reveals molecular differences across sites, with urban samples exhibiting a greater abundance of more oxidized and nitrogen-containing compounds, whereas background samples exhibit broader volatility distributions and relatively lower oxidation states. This work provides an analytical strategy for improving molecular-level analysis of OA and advancing understanding of its composition and atmospheric processes.

Arabian incense (Bakhoor) burning is a widely practiced fragrancing and ceremonial activity, yet how the Bakhoor composition controls particle emissions and oxidative potential remains poorly constrained, especially under repeated use in low-ventilation settings. Here we characterized emissions from Bakhoor burning in a controlled chamber using a charcoal-assisted heating configuration representative of common practice and quantified aerosol oxidative potential using complementary acellular dithiothreitol (DTT) activity and a macrophage-based intracellular oxidative-stress response, with smoldering sidestream cigarette smoke as a benchmark source. Normalized by the initial Bakhoor mass per burn, Bakhoor burning produced particle mass and number emission rates of 670–1690 µg min^-1 g^-1 and (6–7) × 10¹¹ particles min^-1 g^-1, respectively. Ultrafine particles contributed 70–75 % of the total particle number, and their emission rates substantially exceeded those from sidestream cigarette smoke. Across Bakhoor materials, emission magnitude followed a nonlinear power-law relationship with the loading of the hexane-soluble fraction, indicating that this fraction is an important control on particle production. In the acellular assay, the particle mass-normalized DTT consumption rate (OP_DTTm) was approximately 32 pmol min^-1 µg^-1, modestly lower than that of cigarette smoke particles, whereas Bakhoor burning particles elicited stronger intracellular oxidative-stress responses. Ozone aging increased oxidative potential for both sources, and the acellular and cellular responses remained evident after aging equivalent to days of indoor exposure. Overall, Bakhoor burning represents a previously underrecognized source of ultrafine aerosol with substantial oxidative potential.