Over Boreal regions, monoterpenes emitted from the forest are the main precursors for secondary organic aerosol (SOA) formation and the primary driver of the growth of new aerosol particles to ...climatically important cloud condensation nuclei (CCN). Autoxidation of monoterpenes leads to rapid formation of Highly Oxygenated organic Molecules (HOM). We have developed the first model with near-explicit representation of atmospheric new particle formation (NPF) and HOM formation. The model can reproduce the observed NPF, HOM gas-phase composition and SOA formation over the Boreal forest. During the spring, HOM SOA formation increases the CCN concentration by ~10 % and causes a direct aerosol radiative forcing of -0.10 W/m
. In contrast, NPF reduces the number of CCN at updraft velocities < 0.2 m/s, and causes a direct aerosol radiative forcing of +0.15 W/m
. Hence, while HOM SOA contributes to climate cooling, NPF can result in climate warming over the Boreal forest.
Aerosol climate effects are intimately tied to interactions with water. Here we combine hygroscopicity measurements with direct observations about the phase of secondary organic aerosol (SOA) ...particles to show that water uptake by slightly oxygenated SOA is an adsorption‐dominated process under subsaturated conditions, where low solubility inhibits water uptake until the humidity is high enough for dissolution to occur. This reconciles reported discrepancies in previous hygroscopicity closure studies. We demonstrate that the difference in SOA hygroscopic behavior in subsaturated and supersaturated conditions can lead to an effect up to about 30% in the direct aerosol forcing—highlighting the need to implement correct descriptions of these processes in atmospheric models. Obtaining closure across the water saturation point is therefore a critical issue for accurate climate modeling.
Key Points
The low solubility of slightly oxygenated SOA limits its water uptake at RH < 100%
Slightly soluble SOA takes up water mainly by adsorption at RH < 100%
Discrepancy in k for RH < 100% and RH > 100% produces uncertainty in modeled ARI
Ice-nucleating particles (INPs) trigger the formation of cloud ice crystals in the atmosphere. Therefore, they strongly influence cloud microphysical and optical properties and precipitation and the ...life cycle of clouds. Improving weather forecasting and climate projection requires an appropriate formulation of atmospheric INP concentrations. This remains challenging as the global INP distribution and variability depend on a variety of aerosol types and sources, and neither their short-term variability nor their long-term seasonal cycles are well covered by continuous measurements. Here, we provide the first year-long set of observations with a pronounced INP seasonal cycle in a boreal forest environment. Besides the observed seasonal cycle in INP concentrations with a minimum in wintertime and maxima in early and late summer, we also provide indications for a seasonal variation in the prevalent INP type. We show that the seasonal dependency of INP concentrations and prevalent INP types is most likely driven by the abundance of biogenic aerosol. As current parameterizations do not reproduce this variability, we suggest a new mechanistic description for boreal forest environments which considers the seasonal variation in INP concentrations. For this, we use the ambient air temperature measured close to the ground at 4.2 m height as a proxy for the season, which appears to affect the source strength of biogenic emissions and, thus, the INP abundance over the boreal forest. Furthermore, we provide new INP parameterizations based on the Ice Nucleation Active Surface Site (INAS) approach, which specifically describes the ice nucleation activity of boreal aerosols particles prevalent in different seasons. Our results characterize the boreal forest as an important but variable INP source and provide new perspectives to describe these new findings in atmospheric models.
•Emission sources and atmospheric processes dictate the chemical composition of PM.•The chemical composition of PM showed seasonal and day-night variations.•Differences in chemical composition affect ...the toxicological responses.•PM size fractions cause toxicity via different pathways.
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Ambient inhalable particulate matter (PM) is a serious health concern worldwide, but especially so in China where high PM concentrations affect huge populations. Atmospheric processes and emission sources cause spatial and temporal variations in PM concentration and chemical composition, but their influence on the toxicological characteristics of PM are still inadequately understood.
In this study, we report an extensive chemical and toxicological characterization of size-segregated urban air inhalable PM collected in August and October 2013 from Nanjing, and assess the effects of atmospheric processes and likely emission sources. A549 human alveolar epithelial cells were exposed to day- and nighttime PM samples (25, 75, 150, 200, 300 μg/ml) followed by analyses of cytotoxicity, genotoxicity, cell cycle, and inflammatory response.
PM10–2.5 and PM0.2 caused the greatest toxicological responses for different endpoints, illustrating that particles with differing size and chemical composition activate distinct toxicological pathways in A549 cells. PM10–2.5 displayed the greatest oxidative stress and genotoxic responses; both were higher for the August samples compared with October. In contrast, PM0.2 and PM2.5–1.0 samples displayed high cytotoxicity and substantially disrupted cell cycle; August samples were more cytotoxic whereas October samples displayed higher cell cycle disruption. Several components associated with combustion, traffic, and industrial emissions displayed strong correlations with these toxicological responses. The lower responses for PM1.0–0.2 compared to PM0.2 and PM2.5–1.0 indicate diminished toxicological effects likely due to aerosol aging and lower proportion of fresh emission particles rich in highly reactive chemical components in the PM1.0–0.2 fraction.
Different emission sources and atmospheric processes caused variations in the chemical composition and toxicological responses between PM fractions, sampling campaigns, and day and night. The results indicate different toxicological pathways for coarse-mode particles compared to the smaller particle fractions with typically higher content of combustion-derived components. The variable responses inside PM fractions demonstrate that differences in chemical composition influence the induced toxicological responses.
In this study, we utilize aerosol mass spectrometer (AMS) and multi-angle absorption photometer (MAAP) measurements to assess the most predominant source regions of various atmospheric aerosol ...constituents transported to Eastern Finland. The non-refractory composition data from the AMS were measured during three intensive measurements campaigns in autumn 2012, 2014 and 2016, whereas the continuous long-term measurements on equivalent black carbon were conducted in 2012-2017. According to observations, the highest concentrations of particulate organics, sulphate, ammonium and black carbon originated from western parts of Russia and Eastern Europe, whereas Central Europe showed lesser contribution. In addition, exceptionally high concentrations of sulphate and ammonium were associated with the Timan-Pechora basin located in north-western Russia. Assumingly, this phenomenon could be linked to intensive gas flaring activities taking place in the area. We also performed positive matrix factorization analysis of organic fraction measured by the AMS. The trajectory analysis revealed increased concentration fields (CF) for low-volatility oxygenated organic aerosol (LVOOA) and hydrocarbon-like organic aerosol (HOA) in the same areas as for sulphate and ammonium. Meanwhile, the CF of semi-volatile oxygenated organic aerosol (SVOOA) suggested a local origin. To summarize, our results suggest that Western Russia and Eastern Europe are the most important source regions of several long-range transported aerosol constituents for Eastern Finland. Besides influencing the air quality and aerosol chemical composition on a local scale, these regions may also play a crucial role as the pollutants are transported further north, towards the vulnerable Arctic region.
The fraction of gasoline direct-injection (GDI) vehicles
comprising the total vehicle pool is projected to increase in the future.
However, thorough knowledge about the influence of GDI engines on ...important
atmospheric chemistry processes is missing – namely, their contribution to
secondary organic aerosol (SOA) precursor emissions, contribution to SOA formation, and
potential role in biogenic–anthropogenic interactions. The objectives of
this study were to (1) characterize emissions from modern GDI vehicles and
investigate their role in SOA formation chemistry and (2) investigate
biogenic–anthropogenic interactions related to SOA formation from a mixture
of GDI-vehicle emissions and a model biogenic compound, α-pinene.
Specifically, we studied SOA formation from modern GDI-vehicle emissions
during the constant-load driving. In this study we show that SOA formation
from GDI-vehicle emissions was observed in each experiment. Volatile organic compounds (VOCs) measured
with the proton-transfer-reaction time-of-flight
mass spectrometer (PTR-ToF-MS) could account for 19 %–42 % of total SOA mass generated in each experiment. This suggests that there were lower-volatility
intermediate VOCs (IVOCs) and semi-volatile organic compounds (SVOCs) in the GDI-vehicle exhaust that likely contributed to SOA production but were not detected with the
instrumentation used in this study. This study also demonstrates that two distinct mechanisms caused by anthropogenic emissions suppress α-pinene SOA mass yield. The first suppressing effect was the presence of NOx. This mechanism is consistent with previous reports demonstrating suppression of biogenic SOA formation in the presence of anthropogenic emissions. Our results indicate a possible second suppressing effect, and we suggest that the presence of anthropogenic gas-phase species may have suppressed biogenic SOA formation by alterations to the gas-phase chemistry of α-pinene. This hypothesized change in oxidation pathways led to the formation of α-pinene oxidation products that most likely did not have vapor pressures low enough to partition into the particle phase. Overall, the presence of gasoline-vehicle exhaust caused a more than 50 % suppression in α-pinene SOA mass yield compared to the α-pinene SOA mass yield measured in the absence of any anthropogenic influence.
This study presents results of direct observations of aerosol chemical composition in clouds. A high-resolution time-of-flight aerosol mass spectrometer was used to make measurements of cloud ...interstitial particles (INT) and mixed cloud interstitial and droplet residual particles (TOT). The differences between these two are the cloud droplet residuals (RES). Positive matrix factorization analysis of high-resolution mass spectral data sets and theoretical calculations were performed to yield distributions of chemical composition of the INT and RES particles. We observed that less oxidized hydrocarbon-like organic aerosols (HOA) were mainly distributed into the INT particles, whereas more oxidized low-volatile oxygenated OA (LVOOA) mainly in the RES particles. Nitrates existed as organic nitrate and in chemical form of NH4NO3. Organic nitrates accounted for 45% of total nitrates in the INT particles, in clear contrast to 26% in the RES particles. Meanwhile, sulfates coexist in forms of acidic NH4HSO4 and neutralized (NH4)2SO4. Acidic sulfate made up 64.8% of total sulfates in the INT particles, much higher than 10.7% in the RES particles. The results indicate a possible joint effect of activation ability of aerosol particles, cloud processing, and particle size effects on cloud formation.
Experiments for formation of secondary organic aerosol (SOA) from photooxidation of 1,3,5-trimethylbenzene in the CH3ONO/NO/air mixture were carried out in the laboratory chamber. The size and ...chemical composition of the resultant individual particles were measured in real-time by an aerosol laser time of flight mass spectrometer (ALTOFMS) recently designed in our group. We also developed Fuzzy C-Means (FCM) algorithm to classify the mass spectra of large numbers of SOA particles. The study first started with mixed particles generated from the standards benzaldehyde, phenol, benzoic acid, and nitrobenzene solutions to test the feasibility of application of the FCM. The FCM was then used to extract out potential aerosol classes in the chamber experiments. The results demonstrate that FCM allowed a clear identification of ten distinct chemical particle classes in this study, namely, 3,5-dimethylbenzoic acid, 3,5-dimethylbenzaldehyde, 2,4,6-trimethyl-5-nitrophenol, 2-methyl-4-oxo-2-pentenal, 2,4,6-trimethylphenol, 3,5-dimethyl-2-furanone, glyoxal, and high-molecular-weight (HMW) components. Compared to offline method such as gas chromatography–mass spectrometry (GC–MS) measurement, the real-time ALTOFMS detection approach coupled with the FCM data processing algorithm can make cluster analysis of SOA successfully and provide more information of products. Thus ALTOFMS is a useful tool to reveal the formation and transformation processes of SOA particles in smog chambers.
► Formation of SOA from oxidation of 1,3,5-trimethylbenzene, OH, and NOx in chamber. ► ALTOFMS was used to measure the composition of SOA particles in real time. ► FCM algorithm was employed to classify the SOA mass spectra for the first time.
At the National Synchrotron Radiation Laboratory, The University of Science and Technology of China, an atomic and molecular physics beamline with an energy range of 7.5–124 eV has been constructed ...for studying the spectroscopy and dynamics of atoms, molecules and clusters. The undulator‐based beamline, with a high‐resolution spherical‐grating monochromator (SGM), is connected to the atomic and molecular physics end‐station. This end‐station includes a main experimental chamber for photoionization studies and an additional multi‐stage photoionization chamber for photoabsorption spectroscopy. A mid‐photon flux of 5 × 1012 photons s−1 and a high resolving power is provided by this SGM beamline in the energy range 7.5–124 eV. The size of the synchrotron radiation beam spot at the sample is about 0.5 mm in the vertical direction and 1.0 mm in the horizontal direction. Some experimental results of photoionization efficiency spectroscopy and photoabsorption spectroscopy of atoms and molecules are also reported.
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