Sulfate Mass Concentrations Research Articles

The influence of extratropical cross-tropopause mixing on the correlation between ozone and sulfate aerosol in the lowermost stratosphere

Abstract. The chemical composition of the upper troposphere/lower stratosphere region (UTLS) is influenced by horizontal transport of air masses, vertical transport within convective systems and warm conveyor belts, rapid turbulent mixing, as well as photochemical production or loss of species. This results in the formation of the extratropical transition layer (ExTL), which is defined by the vertical structure of CO and has been studied until now mostly by means of trace gas correlations. Here, we extend the analysis to include aerosol particles and derive the sulfate–ozone correlation in central Europe from aircraft in situ measurements during the CAFE-EU (Chemistry of the Atmosphere Field Experiment over Europe)/BLUESKY mission. The mission probed the UTLS during the COVID-19 period with significantly reduced anthropogenic emissions. We operated a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS) to measure the chemical composition of non-refractory aerosol particles in the size range from about 40 to 800 nm. In our study, we find a correlation between the sulfate mass concentration and O3 in the lower stratosphere. The correlation exhibits some variability exceeding the mean sulfate–ozone correlation over the measurement period. Especially during one flight, we observed enhanced mixing ratios of sulfate aerosol in the lowermost stratosphere, where the analysis of trace gases shows tropospheric influence. However, back trajectories indicate that no recent mixing with tropospheric air occurred within the last 10 d. Therefore, we analyzed volcanic eruption databases and satellite SO2 retrievals from the TROPOspheric Monitoring Instrument (TROPOMI) for possible volcanic plumes and eruptions to explain the high amounts of sulfur compounds in the UTLS. From these analyses and the combination of precursor and particle measurements, we conclude that gas-to-particle conversion of volcanic SO2 leads to the observed enhanced sulfate aerosol mixing ratios.

Sulfate Formation Driven by Wintertime Fog Processing and a Hydroxymethanesulfonate Complex With Iron: Observations From Single‐Particle Measurements in Hong Kong

AbstractFog processing has a significant impact on sulfur chemistry in the atmosphere. This study analyzed three winter fog events in Hong Kong using single‐particle aerosol mass spectrometry (SPAMS) and a Monitor for AeRosols and GAses in ambient air (MARGA). Black carbon (BC)‐related carbonaceous particles with substantial sulfate amounts comprised the largest particle number fraction (56.7%). Sulfate mass concentration decreased during fog due to the cloud's effective scavenging, but fog processing notably promoted sulfate formation at the single‐particle level (average peak area increases of 31.2%). Hydroxymethanesulfonate (HMS), an important S(IV) compound and fog tracer, was identified accounting for up to 12% by particle number fraction. Although pH showed a positive correlation (r = 0.53–0.69) with HMS particles in each fog scenario, a negative overall correlation (r = −0.51) was observed. Further analysis revealed that the higher aerosol acidity (pH 0.65–3.11), promoted Fe dissolution, leading to 49% of HMS particles being mixed with Fe, which potentially facilitated sulfate formation via the Fenton reaction. Additionally, around 40% of HMS‐Fe particles are mixed with oxalate, thereby warranting further attention for their potential to cause more intricate sulfur oxidation processes. This study reveals the initial identification of a high mixed‐state of HMS‐Fe, which could potentially serve as a crucial avenue for the formation of sulfate on individual particulate matter. Considering the persistent augmentation of aerosol acidity in the Asian region, this phenomenon necessitates further investigation and attention.

New insights into the influences of firework combustion on molecular composition and formation of sulfur- and halogen-containing organic compounds

Firework (FW) events occur during various festivals worldwide and substantially negatively influence both air quality and human health. However, the effects of FWs on the chemical properties and formation of organic aerosols are far from clear. In this study, fine particulate matter (PM2.5) samples were collected in a suburban area in Qingdao, China during the Chinese Spring Festival. The concentrations of chemical species (especially carbonaceous components) in PM2.5 were measured using a combination of several state-of-the-art techniques. Our results showed that mass concentrations of water-soluble sulfate, potassium and chloride ions, and organic carbon drastically increased and became the predominant components in PM2.5 during FW events. Correspondingly, both the number and fractional contributions of sulfur (S)-containing subgroups (e.g., CHOS and CHONS compounds) and some chlorine (Cl)-containing organic (e.g., CHOSCl and CHONSCl) compounds identified using ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) increased. The S- and Cl-containing compounds unique to the FW display period were identified, and their chemical characterization, sources, and formation mechanisms were elucidated by combining FT-ICR MS and quantum chemical calculations. Our results suggest that FW emissions play notable roles in both primary and secondary organic aerosol formation, especially for CHOS- and Cl-containing organic compounds.

Measurements of particulate methanesulfonic acid above the remote Arctic Ocean using a high resolution aerosol mass spectrometer

Methanesulfonic acid (MSA) is an important product from the oxidation of dimethyl sulfide (DMS), and thus is often used as a tracer for marine biogenic sources and secondary organic aerosol. MSA also contributes to aerosol mass and potentially to the formation of cloud condensation nuclei and new particles. However, measurements of MSA at high temporal resolution in the remote Arctic are scarce, which limits our understanding of its formation, climate change impact and regional transport. Here, we applied a validated quantification method to determine the mass concentration of MSA and non-sea salt sulfate (nss-SO4) in PM2.5 in the marine boundary layer, using a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) during a research cruise to the Arctic and North Atlantic Ocean, between 55 °N and 68 °N (26th May to June 23, 2022). With this method, the concentrations of MSA in the remote Arctic marine boundary layer were determined for the first time. Results show that the average MSA concentration was 0.025 ± 0.03 μg m−3, ranging from <0.01 to 0.32 μg m−3. The lowest MSA level was found towards the northern leg of the cruise (near Sisimut (67 °N)) with air masses from sea ice over the northern polar region, and the highest MSA concentrations were observed over the Atlantic open ocean. The diurnal cycles of gas MSA, particulate MSA and nss-SO4 peaked in the afternoon, about one hour later than that of peak of solar radiation, which suggests that photochemical process is an important mechanism for the conversion of DMS into MSA above the remote ocean. The mass ratio of MSA to nss-SO4 (MSA/nss-SO4) presents a temperature dependence, which indicates that the addition branching pathway favors MSA formation, while thermal decay of intermediate radicals could be a possible pathway for sulfate formation. Finally, we found that the MSA/nss-SO4 ratio is around 0.22-0.25 in the remote northern marine atmosphere.

Influence of Ammonium Sulfate and Ammonium Nitrate on the Properties of Ambient PM2.5 in Zhenjiang

Recently, the contribution of inorganic salts (nitrates in particular) to the mass concentration of particulate matter with an aerodynamic diameter of less than 2.5 μm (PM2.5) has been increasing across China. However, it is urgent to understand how the increased inorganic salts affect the crucial properties of PM2.5. Here, we conducted continuous field observations at Zhenjiang Ecology and Environment Protection Bureau from January 1 to December 31, 2021. The mass concentrations of ammonium sulfate[(NH4)2SO4] and ammonium nitrate (NH4NO3) were calculated using different methods. The contributions of (NH4)2SO4 and NH4NO3 to the extinction coefficient, hygroscopic growth, and acidity of PM2.5 were discussed in detail. Our results demonstrated that the mean mass concentrations of (NH4)2SO4 and NH4NO3 during the study period were (6.5±4.5) and (15.0±13.3) μg·m-3, which contributed (20.5±18.2)% and (34.5±18.4)% to the mass concentration of PM2.5, respectively. The total extinction coefficient of PM2.5 was (224.5±194.2) Mm-1, in which NH4NO3 was the largest contributor[(40.1±20.9)%] followed by (NH4)2SO4[(19.1±10.8)%]. (NH4)2SO4 and NH4NO3 were also the dominant contributors to the hygroscopic growth of PM2.5. In particular, NH4NO3contributed from (53.8±13.4)% to (61.6±14.6)% to the aerosol water content of PM2.5 under pollution conditions. Thus, NH4NO3 was a key air pollutant to be targeted for further improving the visibility and air quality in Zhenjiang in the future. However, the reduction in the precursors of NH4NO3 would lead to an increase in aerosol acidity, particularly in the spring and winter seasons. Our results help us understand the evolution of air quality and the related impacts and also provide important information on air quality improvement in Zhenjiang in the future.

An ephemeral increase in organic carbon, ion ratios, and heavy metal-containing fine particles was screened in a maritime demarcation zone between North and South Korea

Due to its location in a politically and militarily sensitive area as a maritime demarcation between North and South Korea, increasing attention has been given to the chemical and physical changes in atmospheric aerosols on Baengnyeong Island. To observe modifications in the concentrations and components of basic air pollutants, a Korean State Air Quality Monitoring Superstation was established on the island. The monitoring data obtained from the superstation revealed a significant, short-lived increase in mass concentration of SO2, NO2, and nitrate, organic carbon, and heavy metals (especially Pb) in ambient PM2.5, as well as a gradual decrease in mass concentration of PM10, PM2.5, and sulfate in PM2.5 during September 24–27, 2012. Building upon this data, we conducted source appointment of PM2.5 using the positive matrix factorization receptor model (PMF) and identified six major sources: sea-spray aerosols (29.8%), mobile and biogenic aerosols (24.3%), secondary aerosols (20.0%), gunshot residue (11.1%), mineral dust (8.6%), and oil combustion (6.3%). To examine the physicochemical properties of atmospheric particles, 16 samples collected during that period were investigated using a quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA). We analyzed the morphology, mixing state, elemental constituents, and relative elemental atomic concentrations of 2545 individual particles from the aforementioned six sources, with a focus on particles containing Ca, organic carbon, and Pb. The complementary use of PMF and ED-EPMA confirmed that an episode of air pollution, likely resulting from a military exercise or activity, occurred from September 25 to 26 on or near Baengnyeong Island, leading to an increase in aerosols from gunshot residue and oil combustion. The significant increase in the relative number abundance of organic carbon and heavy metal-containing particles precisely matched their mass concentrations from the monitoring data. These findings imply that multiple methods for bulk and single-particle analysis are necessary when addressing important issues related to source appointment of atmospheric particulate matter.

Spatiotemporal analysis of fine particulate matter for India (1980–2021) from MERRA-2 using ensemble machine learning

Particle exposure affects more humans globally than any other air pollutant. However, due to expensive instruments and infrastructural deficiency, a high spatiotemporal network of monitoring stations is not possible, leading to data-scarce regions. Satellite and reanalysis datasets can be implemented to estimate particulate matter, but they do not provide surface concentration and needs to be reconstructed from the components. In this study, a machine learning (ML) framework is implemented to reconstruct PM2.5 from MERRA-2 data components, namely black carbon (BC), organic carbon (OC), dust (DUST), sea salt (SS), and sulfate (SO4) mass concentration. The ground-level data were collected from India's 335 continuous ambient air quality monitoring stations (CAAQMS) and respective MERRA-2 data for 2017–2021 at hourly resolution. Random forest (RF) performs better with train and test scores (R2) of 0.84 and 0.73, respectively, while the empirical equation provides an R2 of only 0.26 on test data. The estimated PM2.5 for Indian states from 1980 to 2021 indicates a significant increase in most cases. However, states in the Indo-Gangetic plain such as Delhi, Punjab, Haryana, and Uttar Pradesh, are the most polluted regions of India. The major shift in concentration is from 2000 onwards, which can be seen as a direct result of the economic liberalization policies implemented in 1991. The results provide evidence for the limitations of the broad application of the empirical equation and the feasibility of ML algorithms as a potential reconstruction technique for developing robust and accurate region-specific models from MERRA-2 data.

Investigation of the stability of nanofluids based on water and carbon nanoparticles synthesized by the electric arc method

In this work, arc discharge synthesis was carried out by sputtering electrodes of various compositions in a helium medium, as a result of which two types of materials containing carbon globules and graphene flakes were obtained. The synthesized materials were characterized with transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy. The effect of the type and concentration of carbon nanoparticles and the type of surfactants on the stability of water-based nanofluids was studied with optical spectroscopy. For carbon globules and water, the mass concentrations of nanoparticles and sodium dodecyl sulfate were determined to obtain a nanofluid based on them stable for 1 month, which are 0.02% and 1%, respectively. It was shown that the use of neonol AF 9-12 at a concentration of 2% didn’t lead to the stabilization of carbon globules with a mass concentration of 0.02% in water. For graphene flakes, the mass concentrations of nanoparticles and stabilizers to obtain a water-based nanofluid stable for 1 month were: 0.02% graphene flakes and 1% SDS, as well as 0.02% graphene flakes and 2% neonol AF 9-12, respectively.

Addressing the difficulties in quantifying droplet number response to aerosol from satellite observations

Abstract. Aerosol–cloud interaction is the most uncertain component of the overall anthropogenic forcing of the climate, in which cloud droplet number concentration (Nd) sensitivity to aerosol (S) is a key term for the overall estimation. However, satellite-based estimates of S are especially challenging, mainly due to the difficulty in disentangling aerosol effects on Nd from possible confounders. By combining multiple satellite observations and reanalysis, this study investigates the impacts of (a) updraft, (b) precipitation, (c) retrieval errors, and (d) vertical co-location between aerosol and cloud on the assessment of S in the context of marine warm (liquid) clouds. Our analysis suggests that S increases remarkably with both cloud-base height and cloud geometric thickness (proxies for vertical velocity at cloud base), consistent with stronger aerosol–cloud interactions at larger updraft velocity for midlatitude and low-latitude clouds. In turn, introducing the confounding effect of aerosol–precipitation interaction can artificially amplify S by an estimated 21 %, highlighting the necessity of removing precipitating clouds from analyses of S. It is noted that the retrieval biases in aerosol and cloud appear to underestimate S, in which cloud fraction acts as a key modulator, making it practically difficult to balance the accuracies of aerosol–cloud retrievals at aggregate scales (e.g., 1∘×1∘ grid). Moreover, we show that using column-integrated sulfate mass concentration (SO4C) to approximate sulfate concentration at cloud base (SO4B) can result in a degradation of correlation with Nd, along with a nearly twofold enhancement of S, mostly attributed to the inability of SO4C to capture the full spatiotemporal variability of SO4B. These findings point to several potential ways forward to practically account for the major influential factors by means of satellite observations and reanalysis, aiming at optimal observational estimates of global radiative forcings due to the Twomey effect and also cloud adjustments.

A new method to quantify particulate sodium and potassium salts (nitrate, chloride, and sulfate) by thermal desorption aerosol mass spectrometry

Abstract. The reaction of sea salt (or biomass burning) particles with sulfuric acid and nitric acid leads to the displacement of chloride relative to sodium (or potassium). We have developed a new particle mass spectrometer to quantify non-refractory and refractory sulfate aerosols (referred to as refractory aerosol thermal desorption mass spectrometer: rTDMS). The combination of a graphite particle collector and a carbon dioxide laser enables high desorption temperature (blackbody equivalent radiation temperature of up to 930 ∘C). Ion signals originating from evolved gas molecules are detected by a quadrupole mass spectrometer. Here we propose a new method to quantify the mass concentrations of sodium nitrate (NaNO3: SN), sodium chloride (NaCl: SC), sodium sulfate (Na2SO4: SS), potassium nitrate (KNO3: PN), potassium chloride (KCl: PC), and potassium sulfate (K2SO4: PS) particles by using the rTDMS. Laboratory experiments were performed to test the sensitivities of the rTDMS to various types of particles. We measured ion signals originating from single-component particles for each compound and found a good linearity (r2&gt;0.8) between the major ion signals and mass loadings. We also measured ion signals originating from internally mixed SN + SC + SS (or PN + PC + PS) particles and found that the temporal profiles of ion signals at m/z 23 (Na+) (or 39; K+) were characterized by three sequential peaks associated with the evolution of the desorption temperature. We tested potential interferences in the quantification of sea salt particles under real-world conditions by artificially generating “modified” sea salt particles from a mixture of diluted seawater and SN (or SS) solution. The SS/SC ratios estimated from the ion signals at m/z 23, 36 (H35Cl+), and 48 (SO+) agreed well with those predicted from the solution concentrations to within ∼10 %. The SN/SC ratios estimated from the ion signals at m/z 30 (NO+) and 36 also agreed with those predicted from the solution concentrations to within ∼15 %, whereas the SN/SC ratios estimated from m/z 23 were significantly lower than the predicted values. Based on these experimental results, the applicability of the rTDMS to ambient measurements of sea salt particles is discussed.

Measurement report: The effect of aerosol chemical composition on light scattering due to the hygroscopic swelling effect

Abstract. Liquid water in aerosol particles has a significant effect on their optical properties, especially on light scattering, whose dependence on chemical composition is investigated here using measurements made in southern Beijing in 2019. The effect is measured by the particle light scattering enhancement f(RH), where RH denotes the relative humidity, which is found to be positively and negatively impacted by the proportions of inorganic and organic matter, respectively. Black carbon is also negatively correlated. The positive impact is more robust when the inorganic matter mass fraction was smaller than 40 % (R=0.93, R: the Pearson's correlation coefficient), becoming weaker as the inorganic matter mass fraction gets larger (R=0.48). A similar pattern was also found for the negative impact of the organic matter mass fraction. Nitrate played a more significant role in aerosol hygroscopicity than sulfate in Beijing. However, the deliquescence point of ambient aerosols was at about RH = 80 % when the ratio of the sulfate mass concentration to the nitrate mass concentration of the aerosol was high (mostly higher than ∼ 4). Two schemes to parameterize f(RH) were developed to account for the deliquescent and non-deliquescent effects. Using only one f(RH) parameterization scheme to fit all f(RH) processes incurs large errors. A piecewise parameterization scheme is proposed, which can better describe deliquescence and reduces uncertainties in simulating aerosol hygroscopicity.

Cloud drop number concentrations over the western North Atlantic Ocean: seasonal cycle, aerosol interrelationships, and other influential factors.

Cloud drop number concentrations (Nd) over the western North Atlantic Ocean (WNAO) are generally highest during the winter (DJF) and lowest in summer (JJA), in contrast to aerosol proxy variables (aerosol optical depth, aerosol index, surface aerosol mass concentrations, surface cloud condensation nuclei (CCN) concentrations) that generally peak in spring (MAM) and JJA with minima in DJF. Using aircraft, satellite remote sensing, ground-based in situ measurement data, and reanalysis data, we characterize factors explaining the divergent seasonal cycles and furthermore probe into factors influencing Nd on seasonal timescales. The results can be summarized well by features most pronounced in DJF, including features associated with cold-air outbreak (CAO) conditions such as enhanced values of CAO index, planetary boundary layer height (PBLH), low-level liquid cloud fraction, and cloud-top height, in addition to winds aligned with continental outflow. Data sorted into high- and low-Nd days in each season, especially in DJF, revealed that all of these conditions were enhanced on the high-Nd days, including reduced sea level pressure and stronger wind speeds. Although aerosols may be more abundant in MAM and JJA, the conditions needed to activate those particles into cloud droplets are weaker than in colder months, which is demonstrated by calculations of the strongest (weakest) aerosol indirect effects in DJF (JJA) based on comparing Nd to perturbations in four different aerosol proxy variables (total and sulfate aerosol optical depth, aerosol index, surface mass concentration of sulfate). We used three machine learning models and up to 14 input variables to infer about most influential factors related to Nd for DJF and JJA, with the best performance obtained with gradient-boosted regression tree (GBRT) analysis. The model results indicated that cloud fraction was the most important input variable, followed by some combination (depending on season) of CAO index and surface mass concentrations of sulfate and organic carbon. Future work is recommended to further understand aspects uncovered here such as impacts of free tropospheric aerosol entrainment on clouds, degree of boundary layer coupling, wet scavenging, and giant CCN effects on aerosol–Nd relationships, updraft velocity, and vertical structure of cloud properties such as adiabaticity that impact the satellite estimation of Nd.

A new parameterization of uptake coefficients for heterogeneous reactions on multi-component atmospheric aerosols.

Based on laboratory studies and field observations, a new parameterization of uptake coefficients for heterogeneous reactions on multi-component aerosols is developed in this work. The equivalent ratio (ER) of inorganic aerosol is used to establish the quantitative relationship between the heterogeneous uptake coefficients and the composition of aerosols. Incorporating the new ER-dependent scheme, the WRF-CUACE model has been applied to simulate sulfate mass concentrations during December 2017 in the Beijing-Tianjin-Hebei region and evaluate the role of aerosol chemical components played in the sulfate formation. Simulated temporal variations and magnitudes of sulfate show good agreement with the observations by using this new scheme. From clean to polluted cases, although both dominant cations and anions increase significantly, the equivalent ratio decreases gradually and is closer to unity, representing the variation of aerosol compositions, which inhibits the heterogeneous uptake of SO2, with the uptake coefficient decreasing from 1 × 10-4 to 5.3 × 10-5. Based on this phenomenon, a self-limitation process for heterogeneous reactions with the increasing secondary inorganic aerosol from clean to polluted cases is proposed.

Ternary heterojunction stabilized photocatalyst of Co-TiO2/g-C3N4 in boosting sulfite oxidation during wet desulfurization

Visible light can promote a catalyst to generate a large number of oxidative free radicals. The photocatalysis of sulfite oxidation is an efficient and economical approach for reclaiming wet desulfurization byproducts. In the present study, a cost-effective photocatalyst with a low metal concentration, namely Co-TiO2/g-C3N4 (CTO/CN), was synthesized using a simplified one-pot hydrothermal procedure. The structure and characteristics of this photocatalyst were assessed using various characterization methods. The as-prepared CTO/CN exhibited enhanced photocatalytic activities for the oxidation of MgSO3, which was 11-fold higher than that of the uncatalyzed benchmark. Under irradiation, ternary heterojunction photocatalyst accelerated the charge transfer, reduced the band gap and enhanced the production of strong oxidizing species (·O2−, ·OH and h+), which promote the formation of the ·SO5− radical, the active species in the MgSO3 oxidation. The as-prepared CTO/CN increased the critical mass concentration of magnesium sulfate from 10% to 19.9%, which reduced the recovery cost of magnesium sulfate. This paper proposes an environmentally friendly strategy for improving the overall performance of wet desulfurization with low cobalt doping levels for photocatalytic oxidation reactions under visible light.

Investigation of Volcanic Emissions in the Mediterranean: “The Etna–Antikythera Connection”

Between 30 May and 6 June 2019 a series of new flanks eruptions interested the south-east flanks of Mt. Etna, Italy, forming lava flows and explosive activity that was most intense during the first day of the eruption; as a result, volcanic particles were dispersed towards Greece. Lidar measurements performed at the PANhellenic GEophysical observatory of Antikythera (PANGEA) of the National Observatory of Athens (NOA), in Greece, reveal the presence of particles of volcanic origin above the area the days following the eruption. FLEXible PARTicle dispersion model (FLEXPART) simulations and satellite-based SO2 observations from the TROPOspheric Monitoring Instrument onboard the Sentinel-5 Precursor (TROPOMI/S5P), confirm the volcanic plume transport from Etna towards PANGEA and possible mixing with co-existing desert dust particles. Lidar and modeled values are in agreement and the derived sulfate mass concentration is approximately 15 μg/m3. This is the first time that Etna volcanic products are monitored at Antikythera station, in Greece with implications for the investigation of their role in the Mediterranean weather and climate.

Superior energy-saving catalyst of Mn@ZIF67 for reclaiming byproduct in wet magnesia desulfurization

Catalyst for sulfite oxidation can substantially reduce the energy penalty on reclaiming the byproduct in wet magnesia desulfurization. Here we reported a novel self-assembled bimetallic catalyst, being accomplished by the in situ incorporation of Mn metal into the metal organic framework (MOF) structure to constitute Mn@ZIF-67. The ultrahigh performance of Mn@ZIF-67 was attributed to its unique hollow structure and exposed active Co sites in the organic skeleton, allowing sufficient contact and diffusion of the reactants. Meanwhile, doping Mn in the MOF skeleton favored to enhance the interaction between Co and sulfite, thus promoting sulfite oxidation by 8.6-folder compared with un-catalysis. The critical mass concentration of magnesium sulfate was increased from 10% to 25%, thus reducing the heat consumption by approximately 75% for sulfate enrichment prior to crystallization. This study serves to cap the oxidation rate of sulfite in wet desulfurization, thus enabling the feasibility to reduce the energy penalty.

Chemical nature and sources of fine particles in urban Beijing: Seasonality and formation mechanisms

To mitigate air pollution in China, a legislative ‘Air Pollution Prevention and Control Action Plan’ has been implemented by the Chinese government since 2013. There is, however, a lack of investigations for long-term trends in the composition, sources and evolution processes of PM1 (particulate matter with diameter less than 1 μm) after the implementation. To evaluate the effectiveness of these control measures, we present a year-long real-time measurement of the chemical composition of PM1 at an urban site in Beijing from November 2014 to November 2015, and the results are compared with previous studies from 2008 to 2013 to gain insights into the variations of the chemical composition and sources of PM1 in Beijing. Large seasonal differences were observed in the mass concentrations of PM1 species and general declining trend was observed in the last seven years. Specifically, the annual averages of mass concentrations in 2014–2015 decrease by 16–43% (PM1), 23–43% (organic aerosol, OA), 38–68% (sulfate), 26–51% (nitrate), 18–33% (ammonium) and 27–38% (chloride) compared to those from 2008 to 2013. During winter and summer, the seasonal mass concentrations of sulfate and nitrate show more significant declines especially in summer 2008 (79% and 81%) and summer 2011 (76% and 77%). The nitrate-to-sulfate ratio is higher in 2014–2015 (1.5 ± 0.6) than that in 2013 (1.0 ± 0.3), largely due to significant reduction in SO2 emissions, suggesting that nitrate is becoming more important than sulfate in particulate pollution in Beijing. OA is the dominant PM1 fraction (>45%) in all seasons and the mass concentrations/contributions of both primary and secondary OA show different seasonality. As for the more oxidized oxygenated OA (MO-OOA) and less oxidized oxygenated OA (LO-OOA), the contributions of MO-OOA are much higher than those of LO-OOA (27–62% vs. 6–26%) in both high-pollution and low-pollution days. Aqueous-phase processes are found to facilitate the formation of MO-OOA while photochemical oxidation formation is a major contributor of LO-OOA in winter, and photochemical oxidation plays a major role in the formation of MO-OOA in summer and fall. The current study provides a comprehensive seasonal comparison of chemical composition and formation of PM1 in Beijing and a pacesetter in tackling PM pollution for other equally polluted megacities, after implementation of more stringent control measures after 2013.

Seasonal contrast in size distributions and mixing state of black carbon and its association with PM&amp;lt;sub&amp;gt;1.0&amp;lt;/sub&amp;gt; chemical composition from the eastern coast of India

Abstract. Over the Indian region, aerosol absorption is considered to have a potential impact on the regional climate, monsoon and hydrological cycle. Black carbon (BC) is the dominant absorbing aerosol, whose absorption potential is determined mainly by its microphysical properties, including its concentration, size and mixing state with other aerosol components. The Indo-Gangetic Plain (IGP) is one of the regional aerosol hot spots with diverse sources, both natural and anthropogenic, but still the information on the mixing state of the IGP aerosols, especially BC, is limited and a significant source of uncertainty in understanding their climatic implications. In this context, we present the results from intensive measurements of refractory BC (rBC) carried out over Bhubaneswar, an urban site in the eastern coast of India, which experiences contrasting air masses (the IGP outflow or coastal/marine air masses) in different seasons. This study helps to elucidate the microphysical characteristics of BC over this region and delineates the IGP outflow from the other air masses. The observations were carried out as part of South West Asian Aerosol Monsoon Interactions (SWAAMI) collaborative field experiment during July 2016–May 2017, using a single-particle soot photometer (SP2) that uses a laser-induced incandescence technique to measure the mass and mixing state of individual BC particles and an aerosol chemical speciation monitor (ACSM) to infer the possible coating material. Results highlighted the distinctiveness in aerosol microphysical properties in the IGP air masses. BC mass concentration was highest during winter (December–February) (∼1.94±1.58 µg m−3), when the prevailing air masses were mostly of IGP origin, followed by post-monsoon (October–November) (mean ∼1.34±1.40 µg m−3). The mass median diameter (MMD) of the BC mass size distributions was in the range 0.190–0.195 µm, suggesting mixed sources of BC, and, further, higher values (∼ 1.3–1.8) of bulk relative coating thickness (RCT) (ratio of optical and core diameters) were seen, indicating a significant fraction of highly coated BC aerosols in the IGP outflow. During the pre-monsoon (March–May), when marine/coastal air masses prevailed, BC mass concentration was lowest (∼0.82±0.84 µg m−3), and larger BC cores (MMD &gt; 0.210 µm) were seen, suggesting distinct source processes, while RCT was ∼ 1.2–1.3, which may translate into higher extent of absolute coating on BC cores, which may have crucial regional climate implications. During the summer monsoon (July–September), BC size distributions were dominated by smaller cores (MMD ≤ 0.185 µm), with the lowest coating indicating fresher BC, likely from fossil fuel sources. A clear diurnal variation pattern of BC and RCT was noticed in all the seasons, and daytime peak in RCT suggested enhanced coating on BC due to the condensable coating material originating from photochemistry. Examination of submicrometre aerosol chemical composition highlighted that the IGP outflow was dominated by organics (47 %–49 %), and marine/coastal air masses contained higher amounts of sulfate (41 %–47 %), while ammonium and nitrate were seen in minor amounts, with significant concentrations only during the IGP air mass periods. The diurnal pattern of sulfate resembled that of the RCT of rBC particles, whereas organic mass showed a pattern similar to that of the rBC mass concentration. Seasonally, the coating on BC showed a negative association with the mass concentration of sulfate during the pre-monsoon season and with organics during the post-monsoon season. These are the first experimental data on the mixing state of BC from a long time series over the Indian region and include new information on black carbon in the IGP outflow region. These data help in improving the understanding of regional BC microphysical characteristics and their climate implications.

Chemical Characteristics and Source Apportionment of Water-Soluble Ions in Atmosphere Aerosols over the East China Sea Island During Winter and Summer

A total of 70 total suspended particulate (TSP) samples were collected from December 2017 to February 2018 and June to August 2018 in Shengsi Islet, East China Sea. In this study, the mass concentrations of water-soluble ions in the TSP (including Na+, K+, NH4+, Mg2+, Ca2+, Cl-, SO42-, NO3-, and MSA) samplers were determined by ion chromatography. The chemical characteristics, seasonal differences, and main sources of water-soluble ions in this background aerosol site were investigated by a multiple-technique analysis combining a HYSPLIT model, correlation analysis of water-soluble ions, and primary component analysis. The results showed that the average mass concentrations of TSP and the main water-soluble inorganic ions (WSIIs) were both high in winter and low in summer; the average mass concentration of total WSIIs in winter was (26.5±16.3) μg·m-3, and in summer was (8.8±3.8) μg·m-3. Secondary inorganic ions (NO3-, SO42-, and NH4+) are the most important ionic components in TSP, which accounted for 86.2% and 74.9% of TWSIIs in winter and summer, respectively. Meanwhile, the study site was affected by seasonal temperature change, long-distance transmission, and summer biogenic sulfates. The mass concentration of nitrate was highest in winter, and the mass concentration of sulfate was highest in summer. Anthropogenic sources were the main source of nss-SO42- in atmospheric aerosols. The analysis of sulfate sources showed that contributions of biogenic sulfates to nss-SO42- were 28.1% and 5.9% in summer and winter, respectively. The results of principal component analysis indicated that the main sources of aerosol chemical composition were marine and anthropogenic sources in summer and winter, respectively. In winter, Cl- showed a certain degree of enrichment due to the influence of human activities, and the average value of the enrichment factor was 38.5%.

Trends and source apportionment of aerosols in Europe during 1980–2018

Abstract. Aerosols have significantly affected health, environment, and climate in Europe. Aerosol concentrations have been declining since the 1980s in Europe, mainly owing to a reduction of local aerosol and precursor emissions. Emissions from other source regions of the world, which have been changing rapidly as well, may also perturb the historical and future trends of aerosols and change their radiative impact in Europe. This study examines trends of aerosols in Europe during 1980–2018 and quantifies contributions from 16 source regions using the Community Atmosphere Model version 5 with Explicit Aerosol Source Tagging (CAM5-EAST). The simulated near-surface total mass concentration of sulfate, black carbon, and primary organic carbon had a 62 % decrease during 1980–2018. The majority of which was contributed to reductions of local emissions in Europe, and 8 %–9 % was induced by a decrease in emissions from Russia–Belarus–Ukraine. With the decreases in the fractional contribution of local emissions, aerosols transported from other source regions are increasingly important for air quality in Europe. During 1980–2018, the decrease in sulfate loading led to a warming effect of 2.0 W m−2 in Europe, with 12 % coming from changes in non-European sources, especially from North America and Russia–Belarus–Ukraine. According to the Shared Socioeconomic Pathways (SSP) scenarios, contributions to the sulfate radiative forcing over Europe from both local European emissions and non-European emissions should decrease at a comparable rate in the next 3 decades, suggesting that future changes in non-European emissions are as important as European emissions for causing possible regional climate change associated with aerosols in Europe.