Contribution Of Aerosols Research Articles

On the chemistry of small waterbodies linked to marine aerosols and local geology on the Windmill Islands and mainland near Casey Station, Antarctica

Context In total, 43 shallow waterbodies were sampled in 1983 in the vicinity of Casey Station and nearby islands in Antarctica. The following physico-chemical parameters were obtained: water and air temperature, pH, conductivity, dissolved oxygen, plus major and minor elements. Aims To identify the physico-chemical characteristics of these waters and determine their origin, and calculate their mineral saturation indices. Methods Waters were analysed using standard methods, including for some elements, flame-atomic absorption spectrometry, spectrophotometry, ion chromatography and gravimetric determination. Mineral saturation indices were calculated using the PHREEQ program. Key results Water salinities were generally low and in the range of 120–1200 mg L−1 (total dissolved solids, TDS), except for one site connected to the sea, and four slightly saline sites. The Na/Cl, Cl/Br and Ca/SO4 ratios of several waters were in the vicinity of seawater ratios, implying a contribution of marine aerosols. However, the Mg/Ca ratio of most waters departed from the seawater ratio, plus there was concordance between the molar ratios of (Na + K)/(Ca + Mg) of many of the waters sampled and those calculated from rock geochemical analyses from diverse lithologies. Such chemical ‘provincialism’ appears to be dictated by rock composition. Nitrate and phosphate concentrations were high in the vicinity of penguin rookeries. Conclusions Two sources of ions are identified, one as marine aerosols as shown by three sets of ratios (Na/Cl, Cl/Br and Ca/SO4) with known marine values, and the other from the weathering of local rocks as shown by (Na + K)/(Ca + Mg) of the lake waters compared to the same ratios for the surrounding rocks. Only a few waterbodies have saturation levels for several carbonate minerals (calcite, aragonite, dolomite and rhodochrosite). Implications Future work is recommended for monitoring the waterbodies surrounding Casey Station as a result of the increased atmospheric CO2 concentration that has occurred over the past 40 years, and likely also with the cessation of building activities around Casey Station.

Dissecting the contributions of organic nitrogen aerosols to global atmospheric nitrogen deposition and implications for ecosystems

ABSTRACT Atmospheric deposition of particulate organic nitrogen (ONp) is a significant process in the global nitrogen cycle and may be pivotally important for N-limited ecosystems. However, past models largely overlooked the spatial and chemical inhomogeneity of atmospheric ONp and were thus deficient in assessing global ONp impacts. We constructed a comprehensive global model of atmospheric gaseous and particulate organic nitrogen (ON), including the latest knowledge on emissions and secondary formations. Using this model, we simulated global atmospheric ONp abundances consistent with observations. Our estimated global atmospheric ON deposition was 26 Tg N yr−1, predominantly in the form of ONp (23 Tg N yr−1) and mostly from wildfires (37%), oceans (22%) and aqueous productions (17%). Globally, ONp contributed as much as 40% to 80% of the total N deposition downwind of biomass-burning regions. Atmospheric ONp deposition thus constituted the dominant external N supply to the N-limited boreal forests, tundras and the Arctic Ocean, and its importance may be amplified in a future warming climate.

Composition and mixing state of individual aerosol particles from northeast Greenland and Svalbard in the Arctic during spring 2018

The Arctic region is warming about four times faster than the rest of the globe, and thus it is important to understand the processes driving climate change in this region. Aerosols are a significant component of the Arctic climate system as they form ice crystals and liquid droplets that control the dynamics of clouds and also directly interact with solar radiation, depending on the compositions and mixing states of individual particles. Here, we report on the characteristics of submicron-sized aerosol particles using transmission electron microscopy obtained at two high Arctic sites, northeast Greenland (Villum Research Station) and Svalbard (Zeppelin Observatory), during spring 2018. The results showed that a dominant compound in the submicron-sized spring aerosols was sulfate, followed by sea salt particles. Both model simulations and observations at the Zeppelin Observatory showed that sea salt particles became more prevalent when low-pressure systems passed by the station. Model simulations indicate that both sampling sites were affected by diffused and diluted long-range transport of anthropogenic aerosols from lower latitudes with negligible influences of biomass burning emissions during the observation period. Overall, the composition of measured aerosol particles from the two Arctic sites was generally similar and showed no apparent variation except for the sea salt fractions. This study shows a general picture of high Arctic aerosol particles influenced by marine sources and diffused long-range transport of anthropogenic sources during the Arctic spring period. These results will contribute to a better knowledge of the aerosol composition and mixing state during the Arctic spring, which helps to understand the contributions of aerosols to the Arctic climate.

Considerable contribution of secondary aerosol to wintertime haze pollution in new target of the latest clean air actions in China

Fine particulate matter (PM2.5) in Northeast China was targeted by national-level clean air policy for the first time in 2022, with the release of Action Plan to eliminate heavy air pollution events. In this study, we investigated sources of PM2.5 during three successive winters in Harbin, a megacity in Northeast China, based on observational results from several recent campaigns in 2018–2021. During the 2020–2021 campaign, daytime and nighttime samples were collected in specific months in addition to 24-h integrated measurements, and the two sets of samples were combined in different ways to run a positive matrix factorization model. The source apportionment results suggested that the resolved secondary organic carbon (SOCPMF) had an uncertainty of ∼12%. Secondary aerosols were found to show the following features for the typical winters without agricultural fires. First, SOCPMF could be properly constrained by results from another widely-used approach for SOC estimation, the elemental carbon-tracer method. Second, secondary PM2.5 calculated using SOCPMF and secondary inorganic ions were generally in line with the independent estimations based on air quality data. Third, secondary components accounted for more than 50% of PM2.5 on average and contributed even more significantly during severe haze episodes, which were the focus of the latest Action Plan. This study also found that the wintertime PM2.5 decreased more slowly during 2017–2021 compared to 2013–2017, by ∼1 and 10 μg/m3 per year, respectively, for the metropolitan area where Harbin is located at. Our results highlighted the importance of secondary aerosols for further improving air quality in Northeast China, and for avoiding heavy pollution as required by the latest Action Plan.

Comparison of methods to estimate aerosol effective radiative forcings in climate models

Abstract. Uncertainty in the effective radiative forcing (ERF) of climate primarily arises from the unknown contribution of aerosols, which impact radiative fluxes directly and through modifying cloud properties. Climate model simulations with fixed sea surface temperatures but perturbed atmospheric aerosol loadings allow for an estimate of how strongly the planet's radiative energy budget has been perturbed by the increase in aerosols since pre-industrial times. The approximate partial radiative perturbation (APRP) technique further decomposes the contributions to the direct forcing due to aerosol scattering and absorption and to the indirect forcing due to aerosol-induced changes in cloud scattering, amount, and absorption, as well as the effects of aerosols on surface albedo. Here we evaluate previously published APRP-derived estimates of aerosol effective radiative forcings from these simulations conducted in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and find that they are biased as a result of two large coding errors that – in most cases – fortuitously compensate. The most notable exception is the direct radiative forcing from absorbing aerosols, which is more than 40 % larger averaged across CMIP6 models in the present study. Correcting these biases eliminates the residuals and leads to better agreement with benchmark estimates derived from double calls to the radiation code. The APRP method – when properly implemented – remains a highly accurate and efficient technique for diagnosing aerosol ERF in cases where double radiation calls are not available, and in all cases it provides quantification of the individual contributors to the ERF that are highly useful but not otherwise available.

Chemical processes of wintertime aerosols over the East China Sea based on aircraft and ground measurements: Comparison with the Sea of Japan

Aircraft and ground-level observations of wintertime aerosols over the East China Sea (ECS) around Japan's southwestern islands were conducted from the boundary layer to the middle troposphere (0–4.5 km) and compared to those over the Sea of Japan (SOJ) during the same period, for the purpose of comprehensive elucidation on modification process of chemical composition in aerosols at the Asian outflow receptor regions. The deficient values of Cl− in both cases for ECS and SOJ were higher at ground level than at high altitudes because of the acidic gas (HNO3, H2SO4) concentrations. Most Na+ and Cl− at high altitudes and at ground level originated from sea salt, because the (Na+ + Cl−) concentrations of which in the boundary layer observed were linearly related to the production flux of sea spray aerosol. The contribution of sea salt aerosols to cloud condensation nuclei appears to be low over the ECS, contrary to the SOJ. The non-sea salt (nss)-K+ concentrations and the path of backward trajectories suggest a significant impact of biomass burning on the SOJ associated with woodburning for residential heating in the Korean Peninsula. A similar difference was observed in NH4+/nss-SO42– equivalent ratios (∼0.5 for the ECS; ∼1 for the SOJ), which likely indicates ammonium sulfate aerosols produced in urban and industrial regions of Korea. The high aerosol Ca2+ concentration in the boundary layer over the ECS was accompanied by those of Na+, Cl−, NO3−, and nss-SO42– during cold front passages, as observed in SOJ. This indicates that Ca(NO3)2, CaSO4, and CaCl2 were formed via the reactions of acidic gases and Ca-rich dust particles from desert areas in the Asian continent, followed by the production of NaNO3 by uptake of acidic gases into sea salt in the ECS. This notion is supported by high Se(VI)/Se (IV) ratios (>2) that indicate an oxidative process during long-range transport from coal combustion sources.

Hemispheric Albedo Asymmetries across Three Phases of CMIP

Abstract Earth’s planetary albedo shows a remarkable hemispheric symmetry. We assess to what extent CMIP models symmetrize the hemispheric clear-sky albedo asymmetry and what the role of clouds is for this. Following Voigt et al., we calculate a reference TOA reflected solar radiation considering the masking of clear-sky asymmetry by symmetric cloud contributions. We use the simple radiation model of Donohoe and Battisti to estimate this benchmark and to separate surface, aerosol, and cloud contributions to the compensation of this benchmark. In CERES, tropical clouds enhance the reference asymmetry while extratropical cloud asymmetries balance the reference asymmetry and the additional asymmetry introduced by tropical clouds. CMIP multimodel means show similar results as CERES. Clouds compensate reference asymmetries by 85% (CMIP3), 65% (CMIP5), and 78% (CMIP6) as compared with 98% for CERES. Spatial distributions of hemispheric differences indicate clear improvements across the CMIP phases. Remaining all-sky reflection asymmetries predominantly result from too-small, partly compensating cloud asymmetries: a too-weak enhancement of the reference asymmetry in the tropical Atlantic and eastern Pacific Oceans is accompanied by a too-weak compensation by extratropical clouds. Thus, tropical clouds and extratropical storm track regions are largely responsible for the compensation of hemispheric clear-sky asymmetries in CERES and CMIP, and for remaining biases in the GCMs. An unexpected result is the magnitude of model biases in the clear-sky asymmetries, which potentially condition systematic cloud biases. Experiments testing cloud-controlling factors influencing hemispheric asymmetry could help us to understand what drives hemispheric cloud differences.

Changing patterns in the highly contributing aerosol types/species across the globe in the past two decades

With the rapidly changing aerosol emissions due to the increase in urbanization, energy consumption, population density, and industrialization in the past two decades across the globe, there is an evolution of different chemical properties of aerosols that are yet not quantified properly. Therefore, a rigorous attempt is made in this study to obtain the long-term changing patterns in the contribution of different aerosol types/species, to the total aerosol loading. This study is carried out only over those regions exhibiting either increasing or decreasing trends in the aerosol optical depth (AOD) parameter on a global scale. Applying the multivariate linear regression trend analysis on Modern-Era Retrospective Analysis for Research and Application version 2 (MERRA-2) aerosol species dataset obtained between 2001 and 2020, we found that despite the overall statistically significant decrease in total columnar AOD trend values over North-Eastern America, and Eastern and Central China regions, an increase in the dust and organic carbon aerosols is observed, respectively. As the uneven vertical distribution of aerosols can alter the direct radiative effects, the extinction profiles of different aerosol types obtained using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) dataset between 2006 and 2020, are further partitioned, for the first time, based on their presence in different altitudes (i.e., within the atmospheric boundary layer and free-troposphere) as well as measurement timing (i.e., daytime and night-time) regimes. The detailed analysis showed that there exists an overall higher contribution of aerosols persisting in the free troposphere region which in turn can have a long-term effect on climate due to their higher residence time, particularly absorbing aerosols. As the trends are mostly associated with the changes in energy use, regional regulatory policies, and/or changing background meteorology conditions, therefore this study also elaborates on the effectiveness of these factors with the changes obtained in different aerosol species/types over the region.

Harmful algal bloom aerosols and human health.

Harmful algal blooms (HABs) are increasing across many locations globally. Toxins from HABs can be incorporated into aerosols and transported inland, where subsequent exposure and inhalation can induce adverse health effects. However, the relationship between HAB aerosols and health outcomes remains unclear despite the potential for population-level exposures. In this review, we synthesized the current state of knowledge and identified evidence gaps in the relationship between HAB aerosols and human health. Aerosols from Karenia brevis, Ostreopsis sp., and cyanobacteria were linked with respiratory outcomes. However, most works did not directly measure aerosol or toxin concentrations and instead relied on proxy metrics of exposure, such as cell concentrations in nearby waterbodies. Furthermore, the number of studies with epidemiological designs was limited. Significant uncertainties remain regarding the health effects of other HAB species; threshold dose and the dose-response relationship; effects of concurrent exposures to mixtures of toxins and other aerosol sources, such as microplastics and metals; the impact of long-term exposures; and disparities in exposures and associated health effects across potentially vulnerable subpopulations. Additional studies employing multifaceted exposure assessment methods and leveraging large health databases could address such gaps and improve our understanding of the public health burden of HABs.

Modelling the effect of aerosol and greenhouse gas forcing on the South Asian and East Asian monsoons with an intermediate-complexity climate model

Abstract. The South Asian and East Asian summer monsoons are globally significant meteorological features, creating a strongly seasonal pattern of precipitation, with the majority of the annual precipitation falling between June and September. The stability the monsoons is of extreme importance for a vast range of ecosystems and for the livelihoods of a large share of the world's population. Simulations are performed with an intermediate-complexity climate model in order to assess the future response of the South Asian and East Asian monsoons to changing concentrations of aerosols and greenhouse gases. The radiative forcing associated with absorbing aerosol loading consists of a mid-tropospheric warming and a compensating surface cooling, which is applied to India, Southeast Asia, and eastern China both concurrently and independently. The primary effect of increased absorbing aerosol loading is a decrease in summer precipitation in the vicinity of the applied forcing, although the regional responses vary significantly. The decrease in precipitation is not ascribable to a decrease in the precipitable water and instead derives from a reduction in the precipitation efficiency due to changes in the stratification of the atmosphere. When the absorbing aerosol loading is added in all regions simultaneously, precipitation in eastern China is most strongly affected, with a quite distinct transition to a low precipitation regime as the radiative forcing increases beyond 60 W m−2. The response is less abrupt as we move westward, with precipitation in southern India being least affected. By applying the absorbing aerosol loading to each region individually, we are able to explain the mechanism behind the lower sensitivity observed in India and attribute it to remote absorbing aerosol forcing applied over eastern China. Additionally, we note that the effect on precipitation is approximately linear with the forcing. The impact of doubling carbon dioxide levels is to increase precipitation over the region while simultaneously weakening the circulation. When the carbon dioxide and absorbing aerosol forcings are applied at the same time, the carbon dioxide forcing partially offsets the surface cooling and reduction in precipitation associated with the absorbing aerosol response. Assessing the relative contributions of greenhouse gases and aerosols is important for future climate scenarios, as changes in the concentrations of these species has the potential to impact monsoonal precipitation.

Optical Properties of Boundary Layer Aerosols From High Spectral Resolution Lidar Measurements in a Polluted Urban Environment (Seoul, Korea)

AbstractContinuous measurements of aerosol extinction coefficient (σext) from the High Spectral Resolution Lidar (HSRL) in Seoul from 2016 to 2018 were used to investigate the diurnal variation of the aerosol optical depth (AOD). Nighttime AOD displayed a larger mean and standard deviation (0.45 ± 0.47) than daytime (0.40 ± 0.29). Hygroscopic growth of aerosols under humid conditions was a key factor in the relative enhancement of nighttime AOD. Taking advantage of the HSRL's vertically resolved measurements, the contribution of aerosols within the boundary layer (BL) and free troposphere (FT) to AOD and its temporal variation were investigated. Unlike the diurnal AOD variation, AOD within the BL (AODBL) showed similar diurnal variations with the mixing layer height (MLH), displaying lower nighttime values with a peak around 14–15 local standard time. However, the low correlation between MLH and AODBL (R2 = 0.06) implied that MLH was not the sole deterministic factor of AODBL. A larger AOD of FT aerosols (AODFT) was observed during spring due to frequent elevated dust layers. Using mean σext within the BL and surface PM10 concentrations, the mass extinction efficiency (MEE) of aerosols in Seoul was estimated. The PM10 MEE showed a mean of 5.40 g m−2 and displayed significant variability by PM2.5 to PM10 ratio, season, and ambient relative humidity. The uncertainty of estimated surface PM10 concentrations was minimized when the seasonality and humidity factor in MEE were taken into account (the normalized mean bias decreased from 10.6%, using a single MEE value, to 6.2%).

A new method for the quantification of ambient particulate-matter emission fluxes

Abstract. An inversion method has been developed in order to quantify the emission fluxes of certain aerosol pollution sources across a wide region in the Northern Hemisphere, mainly in Europe and western Asia. The data employed are the aerosol contribution factors deducted by positive matrix factorization (PMF) on a PM2.5 chemical composition dataset from 16 European and Asian cities for the period 2014 to 2016. The spatial resolution of the method corresponds to the geographic grid cell size of the Lagrangian particle dispersion model (Flexible Particle Dispersion Model, FLEXPART, 1∘ × 1∘) which was utilized for the air mass backward simulations. The area covered is also related to the location of the 16 cities under study. Species with an aerodynamic geometric mean diameter of 400 nm and 3.1 µm and a geometric standard deviation of 1.6 and 2.25, respectively, were used to model the secondary sulfate and dust aerosol transport. Potential source contribution function (PSCF) analysis and generalized Tikhonov regularization were applied so as to acquire potential source areas and quantify their emission fluxes. A significant source area for secondary sulfate on the east of the Caspian Sea is indicated, when data from all stations are used. The maximum emission flux in that area is as high as 10 × 10−12 kg m−2 s−1. When Vilnius, Dushanbe, and Kurchatov data were excluded, the areas with the highest emission fluxes were the western and central Balkans and southern Poland. The results display many similarities to the SO2 emission maps provided by the OMI-HTAP (Ozone Monitoring Instrument-Hemispheric Transport Air Pollution) and ECLIPSE (Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants) databases. For dust aerosol, measurements from Athens, Belgrade, Debrecen, Lisbon, Tirana, and Zagreb are utilized. The west Sahara region is indicated as the most important source area, and its contribution is quantified, with a maximum of 17.6 × 10−12 kg m−2 s−1. When we apply the emission fluxes from every geographic grid cell (1∘ × 1∘) for secondary sulfate aerosol deducted with the new method to air masses originating from Vilnius, a useful approximation to the measured values is achieved.

Chemical composition, sources and evolution of wintertime inorganic and organic aerosols in urban Shanghai, China

China experienced severe haze pollution in the past decades. However, systematic characterization of atmospheric fine particles with advanced measurement techniques has been very scarce in Shanghai, which is the largest megacity in China. Herein, we present the characterization of non-refractory submicron aerosol (NR-PM1) in urban Shanghai during winter 2017 by applying an Aerosol Chemical Speciation Monitor (ACSM, Aerodyne Research Inc.). The NR-PM1 is predominated by organics (43%), followed by nitrate (29%), sulfate (18%), ammonium (7%), and chloride (3%). Regarding the organic aerosol (OA) factors, three organic aerosol factors were identified and classified as hydrocarbon-like organic aerosol (HOA), less-oxygenated organic aerosol (LO-OOA), and more-oxygenated organic aerosol (MO-OOA), which contributed 32%, 22%, and 46% to total organic aerosol respectively. The NR-PM1 composition exhibited an increase in secondary inorganic aerosol (SIA) (sulfate, nitrate and ammonium) contribution from clean episodes (49%) to pollution episodes (59%), while organic aerosol contribution decreased accordingly from 48% to 39%. The strong increase of sulfate in high-relative humidity (RH) pollution episodes indicated that aqueous-phase oxidation of SO2 could be an important formation process for sulfate during particulate air pollution period. The contribution of nitrate was elevated from 25% during clean episodes to 32% during polluted episodes, likely owing to the increase of relative humidity which facilitates the hydrolysis of N2O5 and the gas-to-particle partitioning of hydrophilic NH4NO3 and. Further analysis of atmospheric formation relevance suggested that less-oxygenated organic aerosol formation was mainly driven by aqueous-phase chemistry reactions, whereas photochemical oxidation became an important process for more-oxygenated organic aerosol formation. Meanwhile, less-oxygenated organic aerosol formation may also be influenced by atmospheric oxidative tracer (i.e., Ox), as less-oxygenated organic aerosol exhibited a distinct peak at noon under high-relative humidity condition.

Impact of bubble dynamics on aerosol transport based on CFD analysis

The fundamental process of submicron particle transport through a rising bubble is investigated based on the VOF-LPT method. Since the presence of particle interfacial behavior is generally disregarded in previous studies, an interfacial penetration model is applied in this work to include its effect on the scrubbing efficiency, whereby the process of how bubble dynamics affects aerosol transport is analyzed in detail via parametric studies including Eötvös and Galilei numbers. The results indicated that the dependence of the scrubbing efficiency on increasing Eötvös numbers is non-monotonic, which is linked to the weakened internal flow in the approaching process and the deteriorated surface tension force in the impacting process. By contrast, the decreasing Galilei numbers exert a trapping effect on submicron particles inside scrubbing bubbles, which is manifested as the dampened bubble shape oscillation in the approaching process and the escalated viscous drag in the impacting process. Aerosol removal contributions from different mechanisms are found to be highly dependent on gas-liquid surface tension but insensitive to liquid viscosity for submicron particles. In general, the present method is proven to be viable to simulate the submicron particle transport inside scrubbing bubbles under the circumstance of changeable bubble dynamics.

Role of deep convection on the spatial asymmetry of the UTLS aerosols in the Asian summer monsoon anticyclone region

In this study, we described the spatial asymmetry of the Asian Summer Monsoon Anticyclone (ASMA) circulation using Geopotential Height (GPH) values and divided ASMA into North-West (NW: 32.5°–37.5° N, 40°-70°E), North-East (NE: 32.5°–37.5° N, 70°-100°E), South-West (SW: 27.5°–32.5° N, 40°-70°E) and South-East (SE: 27.5°–32.5° N, 70°-100°E) regions. We provided the spatial asymmetry in the aerosol distribution using the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) (2006–2020) measurements. The vertical distribution of aerosols has been investigated over these regions dividing the atmosphere into (1) Boundary Layer-BL (0–1.5 km), (2) Mid-Troposphere-MT (∼1.5–8 km) and (3) Upper Troposphere and Lower Stratosphere -UTLS (∼8–18 km). Highest aerosol extinction values are noticed in the MT and their contribution to the total Aerosol Optical Depth (AOD) is highest (∼50–80%). The contribution of UTLS aerosols to the total AOD is ∼10% particularly in the eastern part (NE/SE) of the ASMA. The enhancement of aerosols throughout the upper troposphere over the eastern regions (SE/NE) of ASMA, indicates the possible transport of boundary layer pollutants to the UTLS. Using cloud fraction measurements from CloudSat and Pressure vertical velocity (ω), we identified that the intense convection over Bay of Bengal (BoB) is responsible for the UTLS aerosols over the SE region of ASMA. The descending limb of the monsoon-induced circulation over the western region of ASMA (Arabian Peninsula and other Middle Eastern countries) is the possible causative mechanism for the removal of aerosols in the upper troposphere. These findings on the spatial asymmetry in the aerosol distribution over the ASMA are expected to provide the importance of the regional radiative forcing and their climatic impacts.

Spatiotemporal variations of wintertime secondary PM2.5 and meteorological drivers in a basin region over Central China for 2015–2020

It is important to comprehend the contribution of secondary PM2.5 (particulate matter with aerodynamic diameter ≤2.5 μm) to ambient PM2.5 for the long-term change of air quality. This study used the approximate envelope method to identify the variations of primary and secondary PM2.5 concentrations based on routine observations of environment and meteorology in the Twain-Hu Basin (THB, located in Central China), during the winters of 2015–2020. It is found that the contribution of secondary PM2.5 to ambient PM2.5 was enhanced with accompanying the descending trend in PM2.5 concentrations over the recent years. The regional average for secondary PM2.5 contributions was 62.26% in the THB during winters of 2015–2020, and the high secondary contributions were centered in the THB urban areas and major transport routes in the northwestern region. Secondary PM2.5 contributions averaged over the THB increased from 50.41% in clean air quality to 77.09% in heavy PM2.5 pollution with a significant contribution of secondary aerosols to heavy pollution. The secondary PM2.5 contributions presented two peaks at 3:00–7:00 a.m. and 13:00–17:00 p.m., which could be attributed respectively to the nighttime high relative humidity and daytime high air temperature. Regional transport of gaseous precursors of aerosols could lead to the increasing secondary PM2.5 levels in the strong oxidizing atmosphere.

Size-Segregated Characteristics of Organic Carbon (OC) and Elemental Carbon (EC) in Marine Aerosol in the Northeastern South China Sea

Organic carbon (OC) and elemental carbon (EC) size-segregated characteristics were analyzed at the junction of sea and land (JSL) and the marine aerosol during the navigation along the northeastern South China Sea (NSCS), including the shallow ocean (NSCS-SO) and the remote ocean (NSCS-RO), from 3 to 20 March 2016. More than 90% of the OC and EC were concentrated in fine particles, and the OC and EC mean concentrations were 10.1 ± 0.63 and 3.44 ± 0.82, 2.67 ± 1.27 and 0.72 ± 0.36, and 1.41 ± 0.50 and 0.40 ± 0.28 μg m−3 in PM3.0 at the JSL, NSCS-SO, and NSCS-RO, respectively. Approximately 75–83% of OC and 84–98% of EC were found in PM1.5. Three sampling sites showed similar OC mass size distributions that had a dominant peak in the 0.49–0.95 μm size range. The mass mean diameters (MMDs) of OC were 0.65 ± 0.15 and 0.59 ± 0.16 μm at the NSCS-SO and NSCS-RO, respectively, followed by 0.53 ± 0.25 μm in fine particles at the JSL. Similar characteristics were found for EC MMDs. Each particle-size bin had OC concentrations that were higher than the EC values of all three sites, and the OC/EC mass ratios were generally more than 2.0. The mean secondary organic carbon (SOC) concentrations in PM1.5 were as follows: JSL (5.42 ± 1.35 μg m−3) > NSCS-SO (1.08 ± 1.02 μg m−3) > NSCS-RO (0.38 ± 0.25 μg m−3), indicating that the contribution of secondary carbonaceous aerosols to organic carbon is relatively low in the remote ocean region.

Distributions and Trends of the Aerosol Direct Radiative Effect in the 21st Century: Aerosol and Environmental Contributions

AbstractThe aerosol direct radiative effect (ADRE) is controlled by both aerosol distributions and environmental factors, making it interesting and important to quantitatively assess their effects on the ADRE inhomogeneity and climate trends. By analyzing the ADRE in the 21st century from a global reanalysis data set, we find that the spatial variability of the ADRE and its trends can be well explained by a linear regression model. In this model, scattering and absorbing aerosol optical depths (AODs) are used, along with critical environmental variables such as surface albedo and cloud radiative effect, as predictors. Based on this model, we find that approximately 70% of the ADRE inhomogeneity is due to the AOD distributions and the remainder is attributable to environmental factors. This study also shows that a stronger cooling effect of the scattering aerosols in the Northern Hemisphere drives northward cross‐equator meridional energy transport, although this transport exhibits a declining trend over the last two decades. The changes in surface albedo and cloud radiative effect strongly influence the trends in the regional ADRE and the meridional energy transport driven by them. In particular, the reduction of surface albedo (sea ice) is primarily responsible for the enhancement of the cooling ADRE, as well as an associated trend in meridional energy transport, in the Arctic.

Simultaneous profiling of dust aerosol mass concentration and optical properties with polarized high-spectral-resolution lidar

Dust particles originating from arid desert regions can be transported over long distances, presenting severe risks to climate, environment, social economics, and human health at the source and downwind regions. However, there has been a dearth of continuous diurnal observations of vertically resolved mass concentration and optical properties of dust aerosols, which hinders our understanding of aerosol mixing, stratification, aerosol-cloud interactions, and their impacts on the environment. To fill the gap of the insufficient observations, to the best of our knowledge, this work presents the first high-spectral-resolution lidar (HSRL) observation providing days of continuous profiles of the mass concentration, along with particle linear depolarization ratio (PLDR), backscattering coefficient, extinction coefficient and lidar ratio (LR), simultaneously. We present the results of two strong dust events observed by HSRL over Beijing in 2021. The maximum particle mass concentrations reached (1.52 ± 3.5) x103 μg/m3 and (19.48 ± 0.36) x103 μg/m3 for the two dust events, respectively. The retrieved particle mass concentrations and aerosol optical depth (AOD) agree well with the observation from the surface PM10 concentrations and sun photometer with correlation coefficients of 0.90 and 0.95, respectively. The intensive properties of PLDR and LR of the dust aerosols are 0.31 ± 0.02 and 39 ± 7 sr at 532 nm, respectively, which are generally close to those obtained from observations in the downwind areas. Moreover, inspired by the observations from HSRL, a universal analytical relationship is discovered to evaluate the proportion of dust aerosol backscattering, extinction, AOD, and mass concentration using PLDR. The universal analytical relationship reveals that PLDR can directly quantify dust aerosol contribution, which is expected to further expand the application of polarization technology in dust detection. These valuable observations and findings further our understanding of the contribution of dust aerosol to the environment and help supplement dust aerosol databases.

Effects of atmospheric oxidation processes on the latitudinal distribution differences in MSA and nss-SO42- in the Northwest Pacific

Dimethyl sulfide (DMS) derived aerosols play an important role in the oceanic atmosphere. The methanesulfonic acid (MSA)/non-sea-salt sulfate (nss-SO42-) ratio is often used to determine the contribution of the DMS sulfate source. However, there is competition between the pathways of DMS to MSA and sulfate, and the importance of the differences in the reaction pathways for MSA/nss-SO42- remains unclear. Here, the MSA, nss-SO42-, and other environmental data from the Northwest Pacific Ocean in July and September were used to evaluate the impact of atmospheric oxidation processes on the ratio. In July, nss-SO42- was mostly contributed by anthropogenic sources, and in September, it was mostly produced mainly from DMS (biogenic sulfate [bio-SO42-]). Differences in sources explain most of the spatiotemporal distribution characterization of MSA and nss-SO42-. However, the atmospheric oxidation process was the main factor responsible for the difference in the spatial distribution of MSA and bio-SO42- in September. The air temperature, surface incoming shortwave flux, ozone and relative humidity affect atmospheric oxidation processes and thus the MSA/bio-SO42– ratio. Therefore, when nss-SO42- is mainly from the DMS source and the net primary production (NPP) is similar between sea areas, the MSA/nss-SO42- ratio needs to be used carefully to evaluate the sulfate contribution from the DMS source. In addition, it should be noted that the contribution of the DMS source aerosol to the Northwest Pacific is not negligible (up to 45%) with gentle wind and high NPP.