Aerosol particles cool the climate by scattering solar radiation and by acting as cloud condensation nuclei. Higher temperatures resulting from increased greenhouse gas levels have been suggested to ...lead to increased biogenic secondary organic aerosol and cloud condensation nuclei concentrations creating a negative climate feedback mechanism. Here, we present direct observations on this feedback mechanism utilizing collocated long term aerosol chemical composition measurements and remote sensing observations on aerosol and cloud properties. Summer time organic aerosol loadings showed a clear increase with temperature, with simultaneous increase in cloud condensation nuclei concentration in a boreal forest environment. Remote sensing observations revealed a change in cloud properties with an increase in cloud reflectivity in concert with increasing organic aerosol loadings in the area. The results provide direct observational evidence on the significance of this negative climate feedback mechanism.
Secondary organic aerosol (SOA) particles are formed in the atmosphere from condensable oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs). On a global scale, biogenic ...VOCs account for about 90% of VOC emissions and of SOA formation (90 billion kilograms of carbon per year). SOA particles can scatter radiation and act as cloud condensation or ice nuclei, and thereby influence the Earth's radiation balance and climate. They consist of a myriad of different compounds with varying physicochemical properties, and little information is available on the phase state of SOA particles. Gas-particle partitioning models usually assume that SOA particles are liquid, but here we present experimental evidence that they can be solid under ambient conditions. We investigated biogenic SOA particles formed from oxidation products of VOCs in plant chamber experiments and in boreal forests within a few hours after atmospheric nucleation events. On the basis of observed particle bouncing in an aerosol impactor and of electron microscopy we conclude that biogenic SOA particles can adopt an amorphous solid-most probably glassy-state. This amorphous solid state should provoke a rethinking of SOA processes because it may influence the partitioning of semi-volatile compounds, reduce the rate of heterogeneous chemical reactions, affect the particles' ability to accommodate water and act as cloud condensation or ice nuclei, and change the atmospheric lifetime of the particles. Thus, the results of this study challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere and their implications for air quality and climate.
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
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.
Interactions between atmospheric aerosols, clouds, and precipitation impact Earth's radiative balance and air quality, yet remain poorly constrained. Precipitating clouds serve as major sinks for ...particulate matter, but recent studies suggest that precipitation may also act as a particle source. The magnitude of the sources versus sinks, particularly for cloud condensation nuclei (CCN) numbers, remain unquantified. This study analyzes multi‐year in situ observations from tropical and boreal forests, as well as Arctic marine environment, showing links between recent precipitation and enhanced particle concentrations, including CCN‐sized particles. In some cases, the magnitude of precipitation‐related source equals or surpasses corresponding removal effect. Our findings highlight the importance of cloud‐processed material in determining near‐surface particle concentrations and the value of long‐term in situ observations for understanding aerosol particle life cycle. Robust patterns emerge from sufficiently long data series, allowing for quantitative assessment of the large‐scale significance of new phenomena observed in case studies.
Plain Language Summary
Atmospheric aerosols, clouds, and precipitation play a significant role in Earth's temperature regulation and air quality. However, understanding their interactions is still a challenge. While clouds and precipitation help remove particles from the atmosphere, recent research suggests rain could also introduce new particles. The extent of this particle source and its impact on climate are still unknown. In this study, we analyzed years of observational data from clean environments, including tropical and boreal forests and the Arctic marine boundary layer. We discovered that after precipitation, new particles were sometimes added to the surface atmosphere. In some cases, rain introduced as many or even more particles than it removed. Our findings highlight the importance of considering how clouds and rain recycle particles when studying air quality and climate. Long‐term, real‐world observations help us understand atmospheric particle life cycles and identify consistent patterns, ultimately improving our knowledge of the complex interactions between aerosols, clouds, and precipitation.
Key Points
Precipitation can act as a source for particles of varying sizes depending on the environment, reflecting diverse underlying mechanisms
Recycling cloud‐processed material influences near‐surface particle concentrations, emphasizing its relevance for climate model implementation
Studying the time‐dependent instead of total accumulated precipitation elucidates direct versus indirect effects on aerosol populations
Effect of Engine Load on Diesel Soot Particles Virtanen, Annele K. K; Ristimäki, Jyrki M; Vaaraslahti, Kati M ...
Environmental science & technology,
05/2004, Letnik:
38, Številka:
9
Journal Article
Recenzirano
This study concentrates on characterization of nonvolatile fraction of diesel particles. These particles have an impact on earth's radiation balance as well as on health effects of vehicle emissions. ...In addition to composition and size distribution of particles, an important factor affecting their health effects and properties and lifetimes in the atmosphere is their morphology. The effect of engine parameters on soot particle size distributions and also on particle morphology has been studied. It was found that the shape of the size distribution and also the structure of diesel particles depend on engine load. The number distributions were found to obey log-normal assumption. The width of the distribution increased with increasing engine load. The geometric standard deviations of measured distributions varied from 1.7 to 2.1. Simultaneously, the fractal dimension of particles decreased with increasing engine load. The values for mass fractal dimensions based on scaling of particle mass and mobility size were between 2.6 and 2.8. Both electron microscopy and measurements of aerodynamic size versus mobility size suggest that the morphology of particles in different size regimes vary, with the large particles being less compact than the small ones.
Natural aerosol feedbacks are expected to become more important in the future, as anthropogenic aerosol emissions decrease due to air quality policy. One such feedback is initiated by the increase in ...biogenic volatile organic compound (BVOC) emissions with higher temperatures, leading to higher secondary organic aerosol (SOA) production and a cooling of the surface via impacts on cloud radiative properties. Motivated by the considerable spread in feedback strength in Earth System Models (ESMs), we here use two long-term observational datasets from boreal and tropical forests, together with satellite data, for a process-based evaluation of the BVOC-aerosol-cloud feedback in four ESMs. The model evaluation shows that the weakest modelled feedback estimates can likely be excluded, but highlights compensating errors making it difficult to draw conclusions of the strongest estimates. Overall, the method of evaluating along process chains shows promise in pin-pointing sources of uncertainty and constraining modelled aerosol feedbacks.
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.
In addition to climate warming, greater herbivore pressure is anticipated to enhance the emissions of climate-relevant biogenic volatile organic compounds (VOCs) from boreal and subarctic forests and ...promote the formation of secondary aerosols (SOA) in the atmosphere. We evaluated the effects of Epirrita autumnata, an outbreaking geometrid moth, feeding and larval density on herbivore-induced VOC emissions from mountain birch in laboratory experiments and assessed the impact of these emissions on SOA formation via ozonolysis in chamber experiments. The results show that herbivore-induced VOC emissions were strongly dependent on larval density. Compared to controls without larval feeding, clear new particle formation by nucleation in the reaction chamber was observed, and the SOA mass loadings in the insect-infested samples were significantly higher (up to 150-fold). To our knowledge, this study provides the first controlled documentation of SOA formation from direct VOC emission of deciduous trees damaged by known defoliating herbivores and suggests that chewing damage on mountain birch foliage could significantly increase reactive VOC emissions that can importantly contribute to SOA formation in subarctic forests. Additional feeding experiments on related silver birch confirmed the SOA results. Thus, herbivory-driven volatiles are likely to play a major role in future biosphere-vegetation feedbacks such as sun-screening under daily 24 h sunshine in the subarctic.
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