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During the 2017 summertime Arctic cruise observation campaigns, we measured over 290,000 individual submicron particles and clustered them into two inorganic classes (dominated by sea salt, accounting for 38.6% by number fraction) and five organic classes (dominated by natural and anthropogenic organics, 61.4%), presenting a distinct difference in geographic distribution. In the high Arctic and marginal ice zone (81.1–84.6°N) compared with the low Arctic (Chukchi Sea, Svalbard, and Iceland, <80°N), ocean‐derived organic aerosols were more prevalent (73.6% vs. 37.1%). Specifically, we found sharp contrasts in the geographic distributions of OC‐Ca (organics internally mixed with calcium, 29.0% vs. 9.4%) and OC‐S (organics internally mixed with sulfate, 3.2% vs. 21.4%). Utilizing an explainable machine learning technique, we inferred that OC‐Ca was driven by wind‐blown sea ice and/or sea ice floes and/or bubble bursting within sea ice leads under low wind speed conditions in the high Arctic, while OC‐S tended to associate with elemental carbon, sulfate, and higher temperatures, potentially originating from combustion emissions at low latitude regions. Plain Language Summary: Knowledge of the mixing state of individual particles is essential for elucidating their sources, formation mechanisms, atmospheric processes, and assessing their climate effect in the Arctic atmosphere. Here, we investigated the origins and geographic distribution of organic aerosol types using a single‐particle aerosol mass spectrometer during the 8th Chinese Arctic Expedition Research Cruise (Chinese Research Vessel Xuelong) in the summertime over the Arctic Ocean. According to the mixing state, individual organic particles were classified into several ocean‐derived and anthropogenic types. Ocean‐derived types were prevalent in the high Arctic compared with that of anthropogenic type in the low Arctic, and their driven factors were different. Specifically, sea ice fraction was the most important driver for the generation of ocean‐derived OC‐Ca (an aerosol type of organics internally mixed with calcium). OC‐S (an aerosol type of organics internally mixed with sulfate) substantially increased in the low Arctic, most probably driven by combustion sources. Key Points: Submicron organic aerosol types show distinct geographic distributions in the summertime ArcticHigher number fraction of ocean‐derived submicron organic aerosols is observed in the high Arctic than the low ArcticThe proportion of sea ice coverage is a determining factor contributing to the spatial variability of OC‐Ca number fractions. [ABSTRACT FROM AUTHOR]

For earthquake-damaged reinforced concrete structures, the static loading test method is adopted to carry out loading tests under cyclic loading on reinforced concrete beams with different reinforcement rates and columns with different axial compression ratios, and the effect of reinforcing and repairing the damaged reinforced concrete structure by using adhesive steel plates and carbon fiber cloth is investigated. Through comparative studies of structural hysteresis curves and skeleton curves under different reinforcement methods, it is concluded that reinforcement has significantly improved the hysteresis characteristics and ductility of members, and the seismic performance of the carbon fiber reinforcement method is better than that of the steel plate reinforcement. This study provides valuable references and suggestions for practical earthquake-damaged building reinforcement and repair works and seismic reinforcement works. [ABSTRACT FROM AUTHOR]

Traditional statistical methods (TSM) and machine learning (ML) methods have been widely used to separate the effects of emissions and meteorology on air pollutant concentrations, while their performance compared to the chemistry transport model has been less fully investigated. Using the Community Multiscale Air Quality Model (CMAQ) as a reference, a series of experiments was conducted to comprehensively investigate the performance of TSM (e.g., multiple linear regression and Kolmogorov–Zurbenko filter) and ML (e.g., random forest and extreme gradient boosting) approaches in quantifying the effects of emissions and meteorology on the trends of fine particulate matter (PM2.5) during 2013−2017. Model performance evaluation metrics suggested that the TSM and ML methods can explain the variations of PM2.5 with the highest performance from ML. The trends of PM2.5 showed insignificant differences (p > 0.05) for both the emission-related ( PM 2.5 EMI ) and meteorology-related components between TSM, ML, and CMAQ modeling results. PM 2.5 EMI estimated from ML showed the least difference to that from CMAQ. Considering the medium computing resources and low model biases, the ML method is recommended for weather normalization of PM2.5. Sensitivity analysis further suggested that the ML model with optimized hyperparameters and the exclusion of temporal variables in weather normalization can further produce reasonable results in emission-related trends of PM2.5. [ABSTRACT FROM AUTHOR]

Although calcium is known to be enriched in sea spray aerosols (SSAs), the factors that affect its enrichment remain ambiguous. In this study, we examine how environmental factors affect the distribution of water-soluble calcium (Ca 2+) distribution in SSAs. We obtained our dataset from observations taken during the R/V Xuelong research cruise in the Ross Sea, Antarctica, from December 2017 to February 2018. Our observations showed that the enrichment of Ca 2+ in aerosol samples was enhanced under specific conditions, including lower temperatures (<-3.5 ∘ C), lower wind speeds (<7 m s -1), and the presence of sea ice. Our analysis of individual particle mass spectra revealed that a significant portion of calcium in SSAs was likely bound with organic matter (in the form of a single-particle type, OC-Ca, internally mixed organics with calcium). Our findings suggest that current estimations of Ca 2+ enrichment based solely on water-soluble Ca 2+ may be inaccurate. Our study is the first to observe a single-particle type dominated by calcium in the Antarctic atmosphere. Our findings suggest that future Antarctic atmospheric modeling should take into account the environmental behavior of individual OC-Ca particles. With the ongoing global warming and retreat of sea ice, it is essential to understand the mechanisms of calcium enrichment and the mixing state of individual particles to better comprehend the interactions between aerosols, clouds, and climate during the Antarctic summer. [ABSTRACT FROM AUTHOR]

Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering albedo (SSA) and the complex refractive index (m=n-ik) of Icelandic dust from five major emission hotspots were retrieved between 370–950 nm using online measurements of size distribution and spectral absorption (βabs) and scattering (βsca) coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured βabs and βsca increased from 0.90–0.94 at 370 nm to 0.94–0.96 at 950 nm in Icelandic dust from the different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asia. The spectral complex refractive index was retrieved by minimizing the differences between the measured βabs and βsca and those computed using the Mie theory for spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive index (n(λ)) was found to be 1.60–1.61 in the different samples and be independent of wavelength. The imaginary part (k(λ)) was almost constant with wavelength and was found to be around 0.004 at 370 nm and 0.002–0.003 at 950 nm. The estimated complex refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed in Icelandic dust may contribute to its high absorption capacity in the shortwave part of the spectrum. The k(λ) values retrieved for Icelandic dust are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing towards the near-infrared. In Icelandic dust, k(λ) between 660–950 nm was 2–8 times higher than most of the dust samples sourced in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate that has not been accounted for in climate predictions. [ABSTRACT FROM AUTHOR]

A single particle aerosol mass spectrometer (SPAMS) was used to accurately quantify the contribution of vehicle non-exhaust emissions to particulate matter at typical road environment. The PM2.5, black carbon, meteorological parameters and traffic flow were recorded during the test period. The daily trend for traffic flow and speed on TEDA Street showed obvious "M" and "W" characteristics. 6.3 million particles were captured via the SPAMS, including 1.3 million particles with positive and negative spectral map information. Heavy Metal, High molecular Organic Carbon, Organic Carbon, Mixed Carbon, Elemental Carbon, Rich Potassium, Levo-rotation Glucose, Rich Na, SiO3 and other categories were analyzed. The particle number concentration measured by SPAMS showed a good linear correlation with the mass concentrations of PM2.5 and BC, which indicates that the particulate matter captured by the SPAMS reflects the pollution level of fine particulate matter. EC, ECOC, OC, HM and crustal dust components were found to show high values from 7:00–9:00 AM, showing that these chemical components are directly or indirectly related to vehicle emissions. Based on the PMF model, 7 major factors are resolved. The relative contributions of each factor were determined: vehicle exhaust emission (44.8 %), coal-fired source (14.5 %), biomass combustion (12.2 %), crustal dust (9.4 %), ship emission (9.0 %), tires wear (6.6 %) and brake pads wear (3.5 %). The results show that the contribution of vehicle non-exhaust to particulate matter at roadside environment is approximately 10.1 %. Vehicle non-exhaust emissions are the focus of future research in the vehicle pollutant emission control field. [ABSTRACT FROM AUTHOR]

Calcium is known to be enriched in sea spray aerosols (SSA), but its controlling factors and individual mixing states remain ambiguous. Here, we investigate the impact of various environmental factors on the water-soluble calcium (Ca2+) distribution in SSA through R/V Xuelong cruise observations over the Ross Sea, Antarctica, from December 2017 to February 2018. We observed enhanced Ca2+ enrichment in aerosol samples at lower temperatures (< -3.5 °C), lower wind speeds (< 7 m s-1) and in the presence of sea ice. Further individual particle mass spectral analysis indicated that considerable fractions of calcium in SSA likely bind with organic matter (a single-particle type, OC-Ca), which may be neglected in current water-soluble estimation of Ca2+ enrichment. Also, this is the first time that a calcium-dominated single-particle type has been observed in the Antarctic atmosphere. We suggest that a broader focus on individual OC-Ca and its subsequent environmental behavior should be included in future Antarctic atmospheric modeling. Given the context of global warming and sea ice retreat, an understanding of the mechanisms of calcium enrichment and mixing state of individual particles involved is valuable for further recognizing the aerosol-cloud-climate interactions in the Antarctica summer. [ABSTRACT FROM AUTHOR]

Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering albedo (SSA) and the complex refractive index (m = n - ik) of Icelandic dust from five major emission hotspots were retrieved between 370–950 nm using online measurements of size distribution and spectral absorption (βabs) and scattering (βsca) coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured βabs and βsca increased from 0.90–0.94 at 370 nm to 0.94–0.96 at 950 nm in Icelandic dust from the different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asian. The spectral complex refractive index was retrieved by minimizing the differences between the measured βabs and βsca and those computed using the Mie theory for spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive index (n(λ)) was found to be 1.60-1.61 in the different samples and independent on wavelength. The imaginary part (k(λ)) was almost constant with wavelength and was found to be around 0.004 at 370 nm and 0.002–0.003 at 950 nm. The estimated complex refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed in Icelandic dust may contribute to its high absorption capacity in the shortwave spectrum. The k(λ) values retrieved for Icelandic dust are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing toward the near-infrared. In Icelandic dust, k(λ) between 660–950 nm was 2–8 times higher than most of the dust samples sourced in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate which has not been accounted for in climate predictions. [ABSTRACT FROM AUTHOR]

The Arctic is a rapidly changing ecosystem, with complex ice–ocean–atmosphere feedbacks. An important process is new particle formation (NPF), from gas-phase precursors, which provides a climate forcing effect. NPF has been studied comprehensively at different sites in the Arctic, ranging from those in the High Arctic and those at Svalbard to those in the continental Arctic, but no harmonised analysis has been performed on all sites simultaneously, with no calculations of key NPF parameters available for some sites. Here, we analyse the formation and growth of new particles from six long-term ground-based stations in the Arctic (Alert, Villum, Tiksi, Zeppelin Mountain, Gruvebadet, and Utqiaġvik). Our analysis of particle formation and growth rates in addition to back-trajectory analysis shows a summertime maxima in the frequency of NPF and particle formation rate at all sites, although the mean frequency and particle formation rates themselves vary greatly between sites, with the highest at Svalbard and lowest in the High Arctic. The summertime growth rate, condensational sinks, and vapour source rates show a slight bias towards the southernmost sites, with vapour source rates varying by around an order of magnitude between the northernmost and southernmost sites. Air masses back-trajectories during NPF at these northernmost sites are associated with large areas of sea ice and snow, whereas events at Svalbard are associated with more sea ice and ocean regions. Events at the southernmost sites are associated with large areas of land and sea ice. These results emphasise how understanding the geographical variation in surface type across the Arctic is key to understanding secondary aerosol sources and providing a harmonised analysis of NPF across the Arctic. [ABSTRACT FROM AUTHOR]

The Arctic is a rapidly changing ecosystem, with complex ice-ocean-atmosphere feedbacks. An important process new particle formation (NPF) from gas phase precursors, which provide a climate forcing effect. NPF has been studied comprehensively at different sites in the Arctic ranging from those in the high Arctic, those at Svalbard, and those in the continental Arctic, but no harmonized analysis has been performed on all sites simultaneously, with no calculations of key NPF parameters available for some sites. Here, we analyse the formation and growth of new particles from six long-term ground-based stations in the Arctic (Alert, Villum, Tiksi, Mt. Zeppelin, Gruvebadet. & Utqiagvik). Our analysis of particle formation and growth rates, as well as back trajectory analysis shows summertime maxima in frequency of NPF and particle formation rate at all sites, although the mean frequency and particle formation rates themselves vary greatly between sites, highest at Svalbard, and lowest in the high Arctic. Growth rate, condensational sinks and vapour source rates show a slight bias towards the southernmost sites, with vapour source rates varying by around an order of magnitude between the northernmost and southernmost sites. Air masse back trajectories during NPF at these northernmost sites are associated with large areas of sea ice and snow, whereas events at Svalbard are associated with more sea ice and ocean regions. Events at the southernmost sites are associated with large areas of land, and sea ice. These results emphasize how understanding the geographical variation in surface type across the Arctic is key to understanding secondary aerosol sources, and provide harmonised analysis of NPF across the Arctic. [ABSTRACT FROM AUTHOR]

Understanding aerosol–cloud–climate interactions in the Arctic is key to predicting the climate in this rapidly changing region. Whilst many studies have focused on submicrometer aerosol (diameter less than 1 µ m), relatively little is known about the supermicrometer aerosol (diameter above 1 µ m). Here, we present a cluster analysis of multiyear (2015–2019) aerodynamic volume size distributions, with diameter ranging from 0.5 to 20 µ m, measured continuously at the Gruvebadet Observatory in the Svalbard archipelago. Together with aerosol chemical composition data from several online and offline measurements, we apportioned the occurrence of the coarse-mode aerosols during the study period (mainly from March to October) to anthropogenic (two sources, 27 %) and natural (three sources, 73 %) origins. Specifically, two clusters are related to Arctic haze with high levels of black carbon, sulfate and accumulation mode (0.1–1 µ m) aerosol. The first cluster (9 %) is attributed to ammonium sulfate-rich Arctic haze particles, whereas the second one (18 %) is attributed to larger-mode aerosol mixed with sea salt. The three natural aerosol clusters were open-ocean sea spray aerosol (34 %), mineral dust (7 %) and an unidentified source of sea spray-related aerosol (32 %). The results suggest that sea-spray-related aerosol in polar regions may be more complex than previously thought due to short- and long-distance origins and mixtures with Arctic haze, biogenic and likely blowing snow aerosols. Studying supermicrometer natural aerosol in the Arctic is imperative for understanding the impacts of changing natural processes on Arctic aerosol. [ABSTRACT FROM AUTHOR]

Understanding aerosol-cloud-climate interactions in the Arctic is key to predict the climate in this rapidly changing region. Whilst many studies have focused on submicron aerosol (diameter less than 1 µm), relatively little is known about the climate relevance of supermicron aerosol (diameter above 1 µm). Here, we present a cluster analysis of multiyear (2015-2019) aerodynamic volume size distributions with diameter ranging from 0.5 to 20 µm measured continuously at the Gruvebadet Observatory in the Svalbard archipelago. Together with aerosol chemical composition data from several online and offline measurements, we apportioned the occurrence of the coarse-mode aerosols to anthropogenic (two sources, 27%) and natural (three sources, 73%) origins. Specifically, two clusters are related to Arctic haze with high levels of black carbon, sulfate and accumulation mode (0.1-1 µm) aerosol. The first cluster (9%) is attributed to ammonium sulfate-rich Arctic haze particles, whereas the second one (18%) to larger-mode aerosol mixed with sea salt. The three natural aerosol clusters were: open ocean sea spray aerosol (34%), mineral dust (7%), and an unidentified source of sea spray-related aerosol (32%). The results suggest that sea spray-related aerosol in polar regions may be more complex than previously thought due to short/long-distance origins and mixtures with Arctic haze, biogenic and likely snow-blowing aerosols. Studying supermicron natural aerosol in the Arctic is imperative for understanding the impacts of changing natural processes on Arctic aerosol. [ABSTRACT FROM AUTHOR]

Air pollution in megacities represents one of the greatest environmental challenges. Our observed results show that the dramatic NOx decrease (77%) led to significant O3 increases (a factor of 2) during the COVID‐19 lockdown in megacity Hangzhou, China. Model simulations further demonstrate large increases of daytime OH and HO2 radicals and nighttime NO3 radical, which can promote the gas‐phase reaction and nocturnal multiphase chemistry. Therefore, enhanced NO3− and SO42− formation was observed during the COVID‐19 lockdown because of the enhanced oxidizing capacity. The PM2.5 decrease was only partially offset by enhanced aerosol formation with its reduction reaching 50%. In particular, NO3− decreased largely by 68%. PM2.5 chemical analysis reveals that vehicular emissions mainly contributed to PM2.5 under normal conditions in Hangzhou. Whereas, stationary sources dominated the residual PM2.5 during the COVID‐19 lockdown. This study provides evidence that large reductions in vehicular emissions can effectively mitigate air pollution in megacities. Plain Language Summary: Megacities in developing countries such as China and India are facing severe air pollutions. There are still large uncertainties in quantifying the sources of fine particles at the citywide scale due to the synergetic effects of complex aerosol chemistry and transboundary transport. The COVID‐19 lockdown led to the lowest intensity of human activities in recent decades, which provides a unique opportunity to gain insights into the relationship between emission sources and aerosol chemistry. The COVID‐19 lockdown led to significant decreases of PM10, PM2.5, CO, SO2, and NOx, whereas O3 increased by more than a factor of 2 in megacity Hangzhou, China. The filter‐based PM2.5 chemical analysis and model simulation show that although enhanced oxidizing capacity promoted the secondary aerosol formation during the COVID‐19 lockdown, the PM2.5 concentrations still largely decreased by 50%, in which NO3− had the largest decrease of 68% whereas SO42− only decreased by 5%. This result indicates that the reduction in vehicular emissions contributed significantly to the PM2.5 decrease during the COVID‐19 lockdown. We highlight that to mitigate air pollution in megacities, regulations on vehicular emissions, deeper energy and industrial restructuring, and regional joint‐controls should be taken in the future. Key Points: Air pollutants PM10, PM2.5, NOx, CO, and SO2 decreased whereas O3 increased during the COVID‐19 lockdown in megacity HangzhouEnhanced NO3− and SO42− formation caused by the enhanced oxidizing capacity partially offset the decrease of PM2.5 in megacity HangzhouThe contribution of vehicular emissions to PM2.5 was over stationary sources under normal conditions in megacity Hangzhou [ABSTRACT FROM AUTHOR]

Black carbon (BC) not only warms the atmosphere but also affects human health. The nationwide lockdown due to the Coronavirus Disease 2019 (COVID‐19) pandemic led to a major reduction in human activity during the past 30 years. Here, the concentration of BC in the urban, urban‐industry, suburb, and rural areas of a megacity Hangzhou were monitored using a multiwavelength Aethalometer to estimate the impact of the COVID‐19 lockdown on BC emissions. The citywide BC decreased by 44% from 2.30 to 1.29 μg/m3 following the COVID‐19 lockdown period. The source apportionment based on the Aethalometer model shows that vehicle emission reduction responded to BC decline in the urban area and biomass burning in rural areas around the megacity had a regional contribution of BC. We highlight that the emission controls of vehicles in urban areas and biomass burning in rural areas should be more efficient in reducing BC in the megacity Hangzhou. Key Points: BC concentrations during the COVID‐lockdown were reduced by 44% in a megacity of ChinaBC from fossil fuels has the largest reduction in urban area during the COVID‐lockdownVehicles and industrial activities are the major contributors of BC in the megacity, followed by and biomass burning [ABSTRACT FROM AUTHOR]

Water-soluble inorganic ions such as ammonium, nitrate and sulfate are major components of fine aerosols in the atmosphere and are widely used in the estimation of aerosol acidity. However, different experimental practices and instrumentation may lead to uncertainties in ion concentrations. Here, an intercomparison experiment was conducted in 10 different laboratories (labs) to investigate the consistency of inorganic ion concentrations and resultant aerosol acidity estimates using the same set of aerosol filter samples. The results mostly exhibited good agreement for major ions Cl - , SO 42- , NO 3- , NH 4+ and K +. However, F - , Mg 2+ and Ca 2+ were observed with more variations across the different labs. The Aerosol Chemical Speciation Monitor (ACSM) data of nonrefractory SO 42- , NO 3- and NH 4+ generally correlated very well with the filter-analysis-based data in our study, but the absolute concentrations differ by up to 42 %. Cl - from the two methods are correlated, but the concentration differ by more than a factor of 3. The analyses of certified reference materials (CRMs) generally showed a good detection accuracy (DA) of all ions in all the labs, the majority of which ranged between 90 % and 110 %. The DA was also used to correct the ion concentrations to showcase the importance of using CRMs for calibration check and quality control. Better agreements were found for Cl - , SO 42- , NO 3- , NH 4+ and K + across the labs after their concentrations were corrected with DA; the coefficient of variation (CV) of Cl - , SO 42- , NO 3- , NH 4+ and K + decreased by 1.7 %, 3.4 %, 3.4 %, 1.2 % and 2.6 %, respectively, after DA correction. We found that the ratio of anion to cation equivalent concentrations (AE / CE) and ion balance (anions–cations) are not good indicators for aerosol acidity estimates, as the results in different labs did not agree well with each other. In situ aerosol pH calculated from the ISORROPIA II thermodynamic equilibrium model with measured ion and ammonia concentrations showed a similar trend and good agreement across the 10 labs. Our results indicate that although there are important uncertainties in aerosol ion concentration measurements, the estimated aerosol pH from the ISORROPIA II model is more consistent. [ABSTRACT FROM AUTHOR]

To investigate the interannual variations of particulate matter (PM) pollution in winter, this paper examines the pollution characteristics of PM with aerodynamic diameters of less than 2.5 and 10 μm (i.e., PM and PM), and their relationship to meteorological conditions over the Beijing municipality, Tianjin municipality, and Hebei Province-an area called Jing-Jin-Ji (JJJ, hereinafter)-in December 2013-16. The meteorological conditions during this period are also analyzed. The regional average concentrations of PM (PM) over the JJJ area during this period were 148.6 (236.4), 100.1 (166.4), 140.5 (204.5), and 141.7 (203.1) μg m, respectively. The high occurrence frequencies of cold air outbreaks, a strong Siberian high, high wind speeds and boundary layer height, and low temperature and relative humidity, were direct meteorological causes of the low PM concentration in December 2014. A combined analysis of PM pollution and meteorological conditions implied that control measures have resulted in an effective improvement in air quality. Using the same emissions inventory in December 2013-16, a modeling analysis showed emissions of PM to decrease by 12.7%, 8.6%, and 8.3% in December 2014, 2015, and 2016, respectively, each compared with the previous year, over the JJJ area. [ABSTRACT FROM AUTHOR]