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This study aims to investigate the seasonal variation and source identification of fluorescent aerosol particles at the monitoring site of the University of Salento in Lecce, southeastern Italy. Utilizing a wideband integrated bioaerosol sensor (WIBS), this research work analyzes data from two specific monitoring days: one in winter (10 January 2024), marked by significant transport of anthropogenic particles from Eastern Europe, and another in early spring (6 March 2024), characterized by marine aerosol sources and occasional desert dust. This study focuses on the seven WIBS particle categories (A, B, C, AB, AC, BC, ABC), which exhibited distinct characteristics between the two days, indicating different aerosol compositions. Winter measurements revealed a predominance of fine-mode particles, particularly soot and bacteria. In contrast, spring measurements showed larger particles, including fungal spores, pollen fragments, and mineral dust. Fluorescence intensity data further emphasized an increase in biological and organic airborne material in early spring. These results highlight the dynamic nature of fluorescent aerosol sources in the Mediterranean region and the necessity of continuous monitoring for air quality assessments. By integrating WIBS measurements with air mass back-trajectories, this study effectively identifies fluorescent aerosol sources and their seasonal impacts, offering valuable insights into the environmental and health implications of aerosol variability in the investigated Mediterranean area. [ABSTRACT FROM AUTHOR]

Aerosol chemical components such as black carbon (BC) and brown carbon (BrC) regulate aerosol optical properties, which in turn drive the atmospheric radiative forcing estimations due to aerosols. In this study, we used the long-term measurements from AERONET (Aerosol Robotic Network) to better understand the aerosol types and composition with respect to their seasonal and spatial variabilities in peninsular Southeast Asia (PSEA, here defined as Vietnam, Cambodia, Thailand, Laos, and Myanmar). Two methods (i.e., aerosol type cluster and aerosol component retrieval) were applied to determine the aerosol type and chemical composition during the biomass-burning (BB) season. AERONET sites in northern PSEA showed a higher AOD (aerosol optical depth) compared to that of southern PSEA. Differences in land use pattern, geographic location, and weather regime caused much of the aerosol variability over PSEA. Lower single-scattering albedo (SSA) and higher fine-mode fraction (FMF) values were observed in February and March, suggesting the predominance of BB type aerosols with finer and stronger absorbing particles during the dry season. However, we also found that the peak BB month (i.e., March) in northern PSEA may not coincide with the lowest SSA once dust particles have mixed with the other aerosols. Furthermore, we investigated two severe BB events in March of 2014 and 2015, revealing a significant BrC fraction during BB event days. On high AOD days, although the BC fraction was high, the BrC fraction remained low due to lack of aerosol aging. This study highlights the dominance of carbonaceous aerosols in the PSEA atmosphere during the BB season, while also revealing that transported dust particles and BrC aerosol aging may introduce uncertainties into the aerosol radiative forcing calculation. [ABSTRACT FROM AUTHOR]

Abstract Biogenic organic compounds in the surface ocean may significantly alter the cloud‐forming ability of sea spray aerosol and thereby affect the amount of solar radiation reaching the ocean surface. Estimates of the organic mass fraction of sea spray vary widely, and some results show a significant dependence on biological activity in the source seawater. We present airborne observations of the organic mass fraction of individual sea spray particles measured using the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument during the Atmospheric Tomography (ATom) mission, which sampled a wide range of latitudes and altitudes over the remote Atlantic and Pacific Oceans across four seasons, from the marine boundary layer to the upper troposphere. The measured sea spray particles of about 0.15–0.7 μm dry diameter showed higher average organic mass fractions at smaller sizes, but values were low overall, with regional integrated submicron means almost always

In the practice of aerological sounding, along with lidar observations, aerosol backscattering sondes are used at night to study and monitor polar stratospheric clouds, tropospheric and stratospheric aerosol, cirrus clouds, pyroconvection, and volcanic aerosol, as well as to verify remote methods and means of ground-based and satellite-based aerosol observations. For aerosol sondes, a simple two-wave measurement technique is used, which makes it possible to diagnose changes in aerosol composition by color index. There are limitations to the possibilities of the two-wave technique, and they are discussed in this article. Aerological sounding combined with lidar observations expands the wavelength range for multiwavelength studies, and direct measurements of atmospheric temperature increase the accuracy of aerosol sensing. This paper considers the application of three or more wavelength techniques. Data from probe measurements using wavelengths of 470, 528, 850, and 940 nm and lidar sensing at wavelengths of 355 and 532 nm are presented. [ABSTRACT FROM AUTHOR]

Large reductions in anthropogenic emissions of particulate matter and its precursor emissions have occurred since the enactment of the Clean Air Act Amendments of 1990. The Interagency Monitoring of Protected Visual Environments network has measured PM2.5 gravimetric mass (mass of particles with aerodynamic diameters less than 2.5 μm, also referred to here as fine mass, "FM") and speciated PM2.5 aerosol composition at remote sites since 1988. Measured species include inorganic anions such as sulfate, nitrate, and chloride, carbonaceous aerosols such as organic (OC) and elemental carbon (EC), and elemental concentrations used to estimate fine dust (FD). Trends in seasonal and annual mean mass concentrations were calculated from 2000 through 2021, a period that includes the largest reductions in emissions. On average, annual mean FM at remote sites in the continental United States has decreased at a rate of −1.8% yr−1. This reduction is largely due to annual mean trends in sulfate (−6.1% yr−1), nitrate (−2.7% yr−1), EC (−2.2% yr−1), FD (−1.3% yr−1), and OC (−0.9% yr−1), although the OC annual mean trend was insignificant. Seasonal and regional mean FM trends varied significantly, with strong reductions in the East in all seasons due to sulfate reductions, and flat and insignificant trends in summer and fall in the West due to the influence of biomass burning emissions on OC trends. Evaluating regional and seasonal mean trends in aerosol composition helps identify sources that continue to adversely impact air quality and hinder progress in FM reductions due to successful regulatory activity. Plain Language Summary: Particulate matter in the atmosphere is made up of many species that have both anthropogenic and natural sources. Thanks to the Clean Air Act Amendments of 1990, anthropogenic emissions that lead to some particulate matter (PM) have decreased, which has resulted in measurable improvements in air quality in remote regions of the United States. Evaluating trends in aerosol measurements from a large‐scale monitoring network over the past two decades has shown that at remote sites in the United States, some aerosol species, like sulfates, nitrates, and some carbonaceous aerosols, have decreased significantly due to the emission reductions; but others, like mineral dust and carbonaceous aerosols from wildfire smoke, have not. In order to continue to make progress in improving air quality in the United States, targeting future sources for emission reductions will require accurate assessments of the contributions from these sources. Dust and wildfire smoke contributions to PM in remote locations across the United States are now larger fractions compared to two decades ago and will likely continue to grow with climate change. Key Points: Fine mass seasonal mean concentrations have significantly decreased in remote regions of the U.S. in response to regulatory activitySulfate aerosols have decreased at the highest rate, followed by nitrate, elemental carbon, fine dust, and organic carbonFlat and insignificant trends in organic carbon and fine mass at western sites in summer/fall were influenced by biomass smoke emissions [ABSTRACT FROM AUTHOR]

Continuing control efforts in recent decade have notably brought down fine‐particulate‐matter (PM2.5) pollution to compliance with the annual average air quality objective in Hong Kong. However, short‐term (several hours to few days) PM2.5 pollution sporadically occurred in winter and has become a major focus of attention, calling research in characterizing sources and their variations at hourly timescale. This study reports hourly measurements of PM2.5 and its chemical speciation, including molecular and elemental tracers in suburban Hong Kong in 2020 winter. Hourly PM2.5 was 20.3 ± 7.33 μg m−3, dominated by organics and sulfate. We deployed tracer‐based source apportionment using positive matrix factorization, which resolved six secondary and seven primary sources. Sulfate‐rich and nitrate‐rich factors were the leading PM2.5 contributors. Variation in source contributions under different air masses revealed the Pearl River Delta region and coastal areas to the north are main origins. Elevation in secondary sources was the driving factor in causing high PM2.5 polluted hours. During Chinese New Year holiday, firework emissions partially offset the reductions in anthropogenic sources, even leading to an increased PM2.5. Hour‐by‐hour examination of most polluted and firework event hours enhanced understanding on dynamic variations of haze and firework burning evolution. The mass concentration of firework‐derived PM2.5 was notably lower under "prohibition" than "restriction" control scenario (avg. 3.5 vs. 8.4 μg m−3). Our results highlight the effectiveness of tracer‐based source apportionment in revealing hourly PM2.5 source variations and the necessity of regional joint management to lessen the severity of episodic PM2.5 pollution and health risks. Plain Language Summary: Episodic PM2.5 pollution elicits acute health impacts and has attracted increasing attention of the public in recent years, thus impelling the need for understanding PM2.5 source variations at the hourly timescale. We present a comprehensive study of PM2.5 sources based on hourly measurements of PM2.5 in suburban Hong Kong during the winter of 2020. Totally, 20 out of 94 sampling days recorded PM2.5 levels exceeding 25 μg m−3, the World Health Organization IT‐4 air quality guideline for daily PM2.5. Over 200 hourly samples (21% of total) surpassed over 25 μg m−3, which we set as the episode threshold value in this study. Our source apportionment results identified the episodic high PM2.5 hr in Hong Kong was attributed to the large increment in secondary formation processes. Firework emissions had a significant but short‐term impact on air quality during the Chinese New Year holidays (5 consecutive days), and their mass contributions increased by ∼2.4 times when the control policy shifted from "prohibition" to "restriction." The overall findings provide scientific insights for formulating effective control strategies to meet the WHO AQG IT‐4 and to strike a balance between pollution mitigation and the inclusion of fireworks to enhance festive occasions. Key Points: Receptor modeling based on hourly aerosol organic molecular and elemental tracers resolved 13 source factors in suburban Hong KongHourly measurements allowed hourly time‐scale characterization of variations in aerosol chemical composition as well as major sourcesAnalysis of PM2.5 episodes and firework events on an hourly basis offered quantitative source data for devising targeted control measures [ABSTRACT FROM AUTHOR]

Atmospheric mercury plays a crucial role in the biogeochemical cycle of mercury. This study conducted an intensive measurement of atmospheric mercury from 2015 to 2018 at a regional site in eastern China. During this period, the concentration of particle-bound mercury (PBM) decreased by 13%, which was much lower than those of gaseous elemenral mercury (GEM, 30%) and reactive gaseous mercury (GOM, 62%). The gradual decrease in the correlation between PBM and CO, K, and Pb indicates that the influence of primary emissions on PBM concentration was weakening. Moreover, the value of the partitioning coefficient (Kp) increased gradually from 0.05 ± 0.076 m3/μg in 2015 to 0.16 ± 0.37 m3/μg in 2018, indicating that GOM was increasingly inclined to adsorb onto particulate matter. Excluding the influence of meteorological conditions and the primary emissions, the change in aerosol composition is designated as the main trigger factor for the increasing gas-particle partitioning of reactive mercury (RM). The increasing ratio of Cl−, NO3−, and organics (Org) in the chemical composition of particle matters (PM2.5), as well as the decrease in the proportion of SO42−, NH4+, and K+, are conducive to the adsorption of GOM onto particles, forming PBM, which led to an increase of Kp and a lag of PBM reduction compared to GEM and GOM under the continuous control measures of anthropogenic mercury emissions. The evolution of aerosol compositions in recent years affects the migration and transformation of atmospheric mercury, which in turn can affect the biogeochemical cycle of mercury.

Lightning is a leading cause of natural disaster-related mortality in the Indian Subcontinent. Currently, there is a lack of observational evidence supporting the role of aerosol composition in modulating lightning intensity and trends in this region. In this study, we analyzed satellite and reanalysis datasets to examine the association between aerosol properties and lightning intensity over three contrasting geographic regions of Indian subcontinent during the premonsoon season (1998–2022). By comparing lightning and non-lightning days, we found a 0.1 unit increase in total aerosol optical depth specifically on lightning days in all three study areas. Additionally, we observed that the aerosol composition of a region influences convective activity. The presence of dust alongside fine aerosols acts as efficient ice nuclei, thereby stimulating lightning activity in all three regions. Therefore, considering aerosol composition together with local meteorology is essential for accurately predicting lightning flash rates in a region.

Atmospheric deposition of pollutants decreases pH and increases the nutrient concentration in the surface water. To examine its impact on coastal phytoplankton composition and primary production, monthly atmospheric aerosol samples were mixed with coastal waters in the microcosm experiments. These experiments suggested that the biomass of Bacillariophyceae, Dinophyceae and Chlorophyceae were increased and primary production of the coastal waters increased by 3 to 19% due to the addition of aeolian nutrients. The increase in primary production displayed significant relation with a concentration of sulphate and nitrate in the atmospheric aerosols suggesting that both decreases in pH and fertilization enhanced primary production. The impact of acidification on primary production was found to be 22%, whereas 78% was contributed by the nutrient increase. The atmospheric pollution is increasing rapidly over the northern Indian Ocean since past two decades due to rapid industrialization. Hence, it is suggested that the impact of atmospheric pollution on the coastal ecosystem must be included in the numerical models to predict possible changes in the coastal ecosystem due to climate change. [ABSTRACT FROM AUTHOR]

Besides their influence on climate and cloud formation, many organic and inorganic substances in aerosol particles pose a risk to human health. Namely, polycyclic aromatic hydrocarbons (PAH) and heavy metals are suspected to be carcinogenic or acutely toxic. The detection and quantification of such compounds is difficult if only small amounts of particulate matter (PM) are available. In addition, filter samples are often complex and time-consuming to prepare for chromatographic measurements and elemental analysis. Here, we present a method based on high-resolution atmospheric pressure laser desorption ionization mass spectrometry imaging (AP-LDI-MSI) and statistical analysis which allows the analysis and characterization of very small sample quantities (< 30 µg) without any sample preparation. The power and simplicity of the method is demonstrated by two filter samples from heavily polluted mega cities. The samples were collected in Tehran (Iran) and Hangzhou (China) in February 2018. In the course of the measurement, more than 3200 sum formulae were assigned, which allowed a statistical evaluation of colocalized substances within the particles on the filter samples. This resulted in a classification of the different particle types on the filters. Finally, both megacities could be distinguished based on characteristic compounds. In the samples from Tehran, the number of sulphur-containing organic compounds was up to 6 times as high as the samples from Hangzhou, possibly due to the increasing efforts of the Chinese government to reduce sulphur emissions in recent years. Additionally, quantification of 13 PAH species was carried out via standard addition. Especially, the samples from Tehran showed elevated concentrations of PAHs, which in the case of higher-molecular-weight species (> m/z 228) were mostly more than twice as high as in Hangzhou. Both cities showed high levels of heavy metals and potentially harmful organic compounds, although their share of total particulate matter was significantly higher in the samples from Tehran. The pre-treatment of the samples was reduced to a minimum with this method, and only small amounts of particles were required to obtain a comprehensive picture for a specific filter sample. The described method provides faster and better control of air pollution in heavily polluted megacities. [ABSTRACT FROM AUTHOR]

Laser cladding with H13 steel powders was performed and the related material transformations were studied for the particles emitted during this process. Fractions of various sizes of the aerosol particles formed during the laser cladding were collected on a cascade impactor, while the electromobility and the aerodynamic size of the particles were measured using a scanning mobility particle spectrometer and an aerodynamic particle sizer, respectively. The aerosol particles deposited onto the impactor plates were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy, as well as total-reflection X-ray fluorescence and X-ray absorption near-edge structure spectroscopy. Both the concentration and mean oxidation state of the major components were correlated with the aerosol particle size. The ultrafine aerosol particles (with a diameter less than about 100 nm) were predominantly oxidized and formed as the result of an evaporation–oxidation–condensation process sequence. The larger particles (>200 nm in geometric diameter) were primarily the residues of the original metal powder and exhibited a composition change as compared to the as-received metal powder. Correlations between the changes in the concentration ratio of the components were detected and explained. [ABSTRACT FROM AUTHOR]

We have compiled and analyzed a comprehensive data set of field observations of iodine speciation in marine aerosol. The soluble iodine content of fine aerosol (PM1) is dominated by soluble organic iodine (SOI; ∼50%) and iodide (∼30%), while the coarse fraction is dominated by iodate (∼50%), with nonnegligible amounts of iodide (∼20%). The SOI fraction shows an equatorial maximum and minima coinciding with the ocean "deserts," which suggests a link between soluble iodine speciation in aerosol and ocean productivity. Among the major aerosol ions, organic anions and non‐sea‐salt sulfate show positive correlations with SOI in PM1. Alkali cations are positively correlated to iodate and negatively correlated with SOI and iodide in coarse aerosol. These relationships suggest that under acidic conditions iodate is reduced to HOI, which reacts with organic matter to form SOI, a possible source of iodide. In less acidic sea‐salt or dust‐rich coarse aerosols, HOI oxidation to iodate and reaction with organic matter likely compete. Plain Language Summary: Iodine has a profound impact on tropospheric chemistry and plays a key role in in mammalian metabolism. Marine aerosol is an atmospheric iodine reservoir and its carrier to continental food chains. However, the chemistry behind the varying concentrations of iodine‐bearing species observed in aerosol is poorly understood, which hinders model predictions about iodine recycling to the gas phase and accumulation in aerosol. To shed some light on this problem, we have compiled and analyzed a global data set of field observations of iodine speciation in aerosol over the ocean between 1983 and 2018. Comparison of the spatial trends of the relative amounts of soluble iodine species in aerosol and ocean surface remote sensing variables reveals a link to ocean productivity, which points to an important role of organics emitted by the ocean and condensed on aerosol surfaces. Furthermore, the speciation of iodine differs between coarse and fine aerosol, which are originated, respectively, from condensation of gases derived from ocean surface emissions (sulfate aerosol) and aeolian processes (sea salt and dust) and, as a consequence of their different composition, have different pH. Overall, organic matter and acidity emerge from our study as the factors controlling iodine speciation in marine aerosol. Key Points: Iodide and SOI are more abundant in PM1, while the coarse fraction is dominated by iodate; iodide is only 30% lower in the coarse fractionIodine speciation in fine aerosol is related to ocean productivity and present a distinct latitudinal variationDifferent chemical regimes correlated with acidic and alkali ions prevail in fine and coarse aerosol speciation [ABSTRACT FROM AUTHOR]

The summertime high Arctic atmosphere is characterized by extremely low aerosol abundance, such that small natural aerosol inputs have a strong influence on cloud formation and surface temperature. The physical sources and the mechanisms responsible for aerosol formation and development in this climate‐critical and changing region are still uncertain. We report time‐resolved measurements of high Arctic Aitken mode (∼20–60 nm diameter) aerosol composition during August–September 2018. During a significant Aitken mode formation event, the particles were composed of a combination of primary and secondary materials. These results highlight the importance of primary aerosol sources for high Arctic cloud formation, and they imply the action of a poorly understood atmospheric mechanism separating larger particles into multiple sub‐particles. Plain Language Summary: Clouds are an important part of Earth's climate system, in part because they play a role in controlling how much energy passes from the sun to Earth's surface and from Earth's surface out into space. Aerosols, or disperse atmospheric particles, act as seeds onto which water can condense to form cloud droplets. The high Arctic region, near the North Pole, is a unique environment because it often has very low numbers of aerosols, which impacts the formation of clouds and their energy trapping and releasing properties. We set out to learn more about how aerosols form in this remote region, where climate is rapidly changing, with likely impacts on aerosol sources. We measured the composition of small, so‐called ultrafine particles and found that they are made of a combination of sea spray and molecules added onto them as gases from the air. Surprisingly, it seems that sometimes large numbers of particles are formed from the breakup of larger composite particles, a process which has been hypothesized but, if it is occurring, is still not understood. Key Points: Aitken mode (20–60 nm) particles in the summertime high Arctic were composed of aged, organic‐rich sea spray and secondary compoundsAn intense Aitken mode number increase was driven by the atmospheric breakup of pre‐existing aerosol by an unknown mechanism [ABSTRACT FROM AUTHOR]

Tropospheric nitrogen dioxide (NO 2 ) poses a serious threat to the environmental quality and public health. Satellite NO 2 observations have been continuously used to monitor NO 2 variations and improve model performances. However, the accuracy of satellite NO 2 retrieval depends on the knowledge of aerosol optical properties, in particular for urban agglomerations accompanied by significant changes in aerosol characteristics. In this study, we investigate the impacts of aerosol composition on tropospheric NO 2 retrieval for an 18 year global data set from Global Ozone Monitoring Experiment (GOME)-series satellite sensors. With a focus on cloud-free scenes dominated by the presence of aerosols, individual aerosol composition affects the uncertainties of tropospheric NO 2 columns through impacts on the aerosol loading amount, relative vertical distribution of aerosol and NO 2 , aerosol absorption properties, and surface albedo determination. Among aerosol compositions, secondary inorganic aerosol mostly dominates the NO 2 uncertainty by up to 43.5% in urban agglomerations, while organic aerosols contribute significantly to the NO 2 uncertainty by -8.9 to 37.3% during biomass burning seasons. The possible contrary influences from different aerosol species highlight the importance and complexity of aerosol correction on tropospheric NO 2 retrieval and indicate the need for a full picture of aerosol properties. This is of particular importance for interpreting seasonal variations or long-term trends of tropospheric NO 2 columns as well as for mitigating ozone and fine particulate matter pollution.

A lightweight, low-power instrument package to measure, in situ, both (1) the local gaseous environment and (2) the composition and microphysical properties of attendant venusian aerosols is presented. This Aerosol-Sampling Instrument Package (ASIP) would be used to explore cloud chemical and possibly biotic processes on future aerial missions such as multiweek balloon missions and on short-duration (<1 h) probes on Venus and potentially on other cloudy worlds such as Titan, the Ice Giants, and Saturn. A quadrupole ion-trap mass spectrometer (QITMS; Madzunkov and Nikolić, J Am Soc Mass Spectrom 25:1841–1852, 2014) fed alternately by (1) an aerosol separator that injects only aerosols into a vaporizer and mass spectrometer and (2) the pure aerosol-filtered atmosphere, achieves the compositional measurements. Aerosols vaporized <600°C are measured over atomic mass ranges from 2 to 300 AMU at <0.02 AMU resolution, sufficient to measure trace materials, their isotopic ratios, and potential biogenic materials embedded within H2SO4 aerosols, to better than 20% in <300 s for H2SO4 -relative abundances of 2 × 10−9. An integrated lightweight, compact nephelometer/particle-counter determines the number density and particle sizes of the sampled aerosols. [ABSTRACT FROM AUTHOR]

Most of human exposure to atmospheric pollutants occurs indoors, and the components of outdoor aerosols may have been changed in the way before reaching indoor spaces. Here we conducted real‐time online measurements of mass concentrations and chemical composition of black carbon and the non‐refractory species in PM2.5 in an occupied office for approximately one month. The open‐close windows and controlled dampness experiments were also performed. Our results show that indoor aerosol species primarily originate from outdoors with indoor/outdoor ratio of these species typically less than unity except for certain organic aerosol (OA) factors. All aerosol species went through filtration upon transport indoors. Ammonium nitrate and fossil fuel OA underwent evaporation or particle‐to‐gas partitioning, while less oxidized secondary OA (SOA) underwent secondary formation and cooking OA might have indoor sources. With higher particulate matter (PM) mass concentration outdoors than in the office, elevated natural ventilation increased PM exposure indoors and this increased exposure was prolonged when outdoor PM was scavenged. We found that increasing humidity in the office led to higher indoor PM mass concentration particularly more oxidized SOA. Overall, our results highlight that indoor exposure of occupants is substantially different from outdoor in terms of mass concentrations and chemical species. [ABSTRACT FROM AUTHOR]

Laser cladding with H13 steel powders was performed and the related material transformations were studied for the particles emitted during this process. Fractions of various sizes of the aerosol particles formed during the laser cladding were collected on a cascade impactor, while the electromobility and the aerodynamic size of the particles were measured using a scanning mobility particle spectrometer and an aerodynamic particle sizer, respectively. The aerosol particles deposited onto the impactor plates were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy, as well as total-reflection X-ray fluorescence and X-ray absorption near-edge structure spectroscopy. Both the concentration and mean oxidation state of the major components were correlated with the aerosol particle size. The ultrafine aerosol particles (with a diameter less than about 100 nm) were predominantly oxidized and formed as the result of an evaporation–oxidation–condensation process sequence. The larger particles (>200 nm in geometric diameter) were primarily the residues of the original metal powder and exhibited a composition change as compared to the as-received metal powder. Correlations between the changes in the concentration ratio of the components were detected and explained.

• Aerosol composition in central China plain was dominated by nitrate and organics. • Air pollution in central China plain (CCP) was relatively homogeneously distributed. • The effect of local emission controls in mitigating air pollution in CCP is limited. Extensive studies on aerosol chemistry have been carried out in megacities in China, however, aerosol characterization in Central China Plain (CCP) is limited. Here we conducted real-time measurements of fine particle composition with a time-of-flight aerosol chemical speciation monitor in Kaifeng, Henan province in October 2019. Our results showed that nitrate and organics constituted the major fraction of non-refractory PM 2.5 for the entire study, on average accounting for 34% and 33%, respectively. However, aerosol composition was substantially different among four periods due to different meteorological conditions and chemical processing. For instance, nitrate presented the lowest contribution during the first period due to evaporative loss associated with high temperature (T), and then rapidly increased during polluted periods as a function of relative humidity (RH). Positive matrix factorization analysis showed the dominance of secondary organic aerosol (SOA) in OA, and also the changes in OA composition under different T and RH levels. In addition, this study is unique with two periods of local emission controls. Back trajectory and coefficient of divergence analysis showed that air pollution in CCP was overall homogeneously distributed. As a result, the effectiveness of local emission controls in this region was strongly affected by meteorological conditions and regional transport. We found that one of the periods with emission control even showed the highest concentrations for the entire study. Our results point towards the limited effect of local emission controls in mitigating air pollution in CCP, and highlight the importance of joint emission controls under unfavorable meteorological conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, we describe the compilation and homogenization of an extensive data set of aerosol iodine field observations in the period between 1963 and 2018 and we discuss its spatial and temporal dependences by comparison with CAM‐Chem model simulations. A close to linear relationship between soluble and total iodine in aerosol is found (∼80% aerosol iodine is soluble), which enables converting a large subset of measurements of soluble iodine into total iodine. The resulting data set shows a distinct latitudinal dependence, with an enhancement toward the Northern Hemisphere (NH) tropics and lower values toward the poles. This behavior, which has been predicted by atmospheric models to depend on the global distribution of the main oceanic iodine source (which in turn depends on the reaction of ozone with aqueous iodide on the sea water‐air interface, generating gas‐phase I2 and HOI), is confirmed here by field observations for the first time. Longitudinally, there is some indication of a wave‐one profile in the tropics, which peaks in the Atlantic and shows a minimum in the Pacific. New data from Antarctica show that the south polar seasonal variation of iodine in aerosol mirrors that observed previously in the Arctic, with two equinoctial maxima and the dominant maximum occurring in spring. While no clear seasonal variability is observed in NH middle latitudes, there is an indication of different seasonal cycles in the NH tropical Atlantic and Pacific. Long‐term trends cannot be unambiguously established as a result of inhomogeneous time and spatial coverage and analytical methods. Plain Language Summary: Iodine is a key trace element in continental food chains whose major global source is oceanic surface gas emissions of iodine‐bearing molecules to the atmosphere. Atmospheric chemical processing of these substances is followed by incorporation of the iodine‐bearing products into airborne marine aerosol particles, which are the carriers of iodine to the continents. In this work, we compile a data set of aerosol composition measurements reporting iodine concentrations at many different locations, seasons, and years. Analysis of the variation of the concentration iodine in aerosol with latitude and longitude enables us to confirm the main mechanism emitting iodine from the oceans, which is triggered by deposition of ozone on the water‐air interface. In addition, we analyze the seasonal variation of the iodine concentration in aerosol in different locations, which also sheds light onto additional iodine sources to the atmosphere. Finally, long‐term trends cannot be unambiguously established, but the observations are compatible with the model‐predicted enhancement of aerosol iodine as a result of increased oceanic iodine emissions over the last 50 years related to ozone pollution. Key Points: Soluble aerosol iodine field observations can be combined with total aerosol iodine data to build a longer term global homogenized data setSoluble iodine represents approximately 80% of total aerosol iodine, while aerosol iodine amounts to about 30% of total atmospheric iodineThe spatial distribution of aerosol iodine provides the first global‐scale observational evidence of the major source of atmospheric iodine [ABSTRACT FROM AUTHOR]

Integrating nephelometers are designed to measure the scattering coefficient, b sp , of an aerosol introduced into its sampling chamber. They have been and are used extensively in laboratory studies and short-term intensive aerosol characterization studies to validate and improve optical aerosol models. They are used to measure long-term temporal and spatial trends of the particle scattering coefficient, and to measure trends in the scattering enhancement factor, f(RH). The National Park Service (NPS) has operated Optec NGN nephelometers with an open sampling chamber, referred to as NGN ambient , designed to measure total (coarse plus fine) particle scattering at near ambient relative humidity (RH). However, the NGN is no longer manufactured and will be replaced with Ambilabs 2WIN nephelometers. An intercomparison study was initiated to compare the NGN ambient , an enclosed heated NGN, two 2WIN nephelometers, one held at RH ≤ 40% and another modified to sample at near ambient RH, and a TSI (Shoreview, MN, USA). The objective of the study was to evaluate the suitability of the 2WIN to replace the NGN ambient and more generally to assess the suitability of the 2WIN instrument to be used to track long term trends in bsp and f(RH) values. The two 2WIN's, TSI and the heated NGN have enclosed sampling chambers with PM2.5 inlets. Measurements of particle physical and chemical properties and sampling chamber RH allowed for an assessment of the inter-comparability of relationships between optical models and nephelometer measurements. Heating of the sampling chamber to reduce RH to less than 40% did not significantly volatilize particle nitrate but heating to reduce the RH to near 20% did. It was also determined that measurement of the scattering enhancement function, f(RH) , was underestimated in this study, by about 20% for RH levels of 70% or greater, when the reference RH nephelometer was held at RH ≤ 40% compared to when the RH ≤ 10%. The study highlighted the importance of careful calibration of the instrument and careful documentation of the sampling chamber environment in which the measurement is made. Knowing precisely the RH in the sensor volume is critical to the interpretation of measured b sp levels. Monitoring of long-term temporal and spatial trends should be done either with the sampling chamber at or near ambient RH to track changes in ambient b sp or at RH ≤ 10% to understand changes in particulate mass concentrations contributing to b sp. Understanding changes in f(RH) over time and space should be done with the reference b sp at RH ≤ 10%. The lower RH levels should be achieved by some method other than heating the chamber to avoid volatilization of the aerosol species such as ammonium nitrate. Key Points. • When atmospheric particle size and physical and chemical characteristics are known it is possible to estimate particulate scattering as measured by a nephelometer if operation of the nephelometer does not inadvertently modify the aerosol, for example heating the aerosol such that volatile species are lost. • Even though nephelometers are easily and accurately calibrated the measurement of particulate scattering is very sensitive to temperature and RH in the sampling chamber. Therefore, to track long-term spatial and temporal trends in aerosol scattering it is critical to control the humidity in the sampling chamber, preferably at relative humidity levels near 20% or less and by some method other than heating the aerosol. • All commercially available nephelometers modify the aerosol because of inadvertent heating and modifications must be made to the nephelometers to operate at near-ambient conditions. • Slight heating of the aerosol such that relative humidity did not exceed 40% in this study apparently did not volatilize ammonium nitrate particles. [ABSTRACT FROM AUTHOR]

Mineral dust aerosols often observed over California in winter and spring, associated with long-range transport from Asia and the Sahara, have been linked to enhanced precipitation based on observations. Local anthropogenic pollution, on the other hand, was shown in previous observational and modeling studies to reduce precipitation. Here we incorporate recent developments in ice nucleation parameterizations to link aerosols with ice crystal formation in a spectral-bin cloud microphysical model coupled with the Weather Research and Forecasting (WRF) model in order to examine the relative and combined impacts of dust and local pollution particles on cloud properties and precipitation type and intensity. Simulations are carried out for two cloud cases (from the CalWater 2011 field campaign) with contrasting meteorology and cloud dynamics that occurred on 16 February (FEB16) and 2 March (MAR02). In both cases, observations show the presence of dust and biological particles in a relative pristine environment. The simulated cloud microphysical properties and precipitation show reasonable agreement with aircraft and surface measurements. Model sensitivity experiments indicate that in the pristine environment, the dust and biological aerosol layers increase the accumulated precipitation by 10–20% from the Central Valley to the Sierra Nevada for both FEB16 and MAR02 due to a ~40% increase in snow formation, validating the observational hypothesis. Model results show that local pollution increases precipitation over the windward slope of the mountains by a few percent due to increased snow formation when dust is present, but reduces precipitation by 5–8% if dust is removed on FEB16. The effects of local pollution on cloud microphysics and precipitation strongly depend on meteorology, including cloud dynamics and the strength of the Sierra Barrier Jet. This study further underscores the importance of the interactions between local pollution, dust, and environmental conditions for assessing aerosol effects on cold-season precipitation in California.

Arctic column ozone reached record low values (∼310 DU) during March of 2011, exposing Arctic ecosystems to enhanced UV-B. We identify the cause of this anomaly using the Oslo CTM2 atmospheric chemistry model driven by ECMWF meteorology to simulate Arctic ozone from 1998 through 2011. CTM2 successfully reproduces the variability in column ozone, from week to week, and from year to year, correctly identifying 2011 as an extreme anomaly over the period. By comparing parallel model simulations, one with all Arctic ozone chemistry turned off on January 1, we find that chemical ozone loss in 2011 is enhanced relative to previous years, but it accounted for only 23% of the anomaly. Weakened transport of ozone from middle latitudes, concurrent with an anomalously strong polar vortex, was the primary cause of the low ozone When the zonal winds relaxed in mid-March 2011, Arctic column ozone quickly recovered.

Fires in agricultural ecosystems emit greenhouse gases and aerosols that influence climate on multiple spatial and temporal scales. Annex 1 countries of the United Nations Framework Convention on Climate Change (UNFCCC), many of which ratified the Kyoto Protocol, are required to report emissions of CH4 and N2O from these fires annually. In this study, we evaluated several aspects of this reporting system, including the optimality of the crops targeted by the UNFCCC globally and within Annex 1 countries, and the consistency of emissions inventories among different countries. We also evaluated the success of individual countries in capturing interannual variability and long-term trends in agricultural fire activity. In our approach, we combined global high-resolution maps of crop harvest area and production, derived from satellite maps and ground-based census data, with Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) measurements of active fires. At a global scale, we found that adding ground nuts (e.g., peanuts), cocoa, cotton and oil palm, and removing potato, oats, rye, and pulse other from the list of 14 crops targeted by the UNFCCC increased the percentage of active fires covered by the reporting system by 9%. Optimization led to a different recommended list for Annex 1 countries, requiring the addition of sunflower, cotton, rapeseed, and alfalfa and the removal of beans, sugarcane, pulse others, and tuber-root others. Extending emissions reporting to all Annex 1 countries (from the current set of 19 countries) would increase the efficacy of the reporting system from 6% to 15%, and further including several non-Annex 1 countries (Argentina, Brazil, China, India, Indonesia, Thailand, Kazakhstan, Mexico, and Nigeria) would capture over 55% of active fires in croplands worldwide. Analyses of interannual trends from the United States and Australia showed the importance of both intensity of fire use and crop production in controlling year-to-year variations in agricultural fire emissions. Remote sensing provides an effective means for evaluating some aspects of the current UNFCCC emissions reporting system; and, if combined with census data, field experiments and expert opinion, has the potential to improve the robustness of the next generation inventory system.

Coupled-carbon-climate simulations are an essential tool for predicting the impact of human activity onto the climate and biogeochemistry. Here we incorporate prognostic desert dust and anthropogenic aerosols into the CCSM3.1 coupled carbon-climate model and explore the resulting interactions with climate and biogeochemical dynamics through a series of transient anthropogenic simulations (20th and 21st centuries) and sensitivity studies. The inclusion of prognostic aerosols into this model has a small net global cooling effect on climate but does not significantly impact the globally averaged carbon cycle; we argue that this is likely to be because the CCSM3.1 model has a small climate feedback onto the carbon cycle. We propose a mechanism for including desert dust and anthropogenic aerosols into a simple carbon-climate feedback analysis to explain the results of our and previous studies. Inclusion of aerosols has statistically significant impacts on regional climate and biogeochemistry, in particular through the effects on the ocean nitrogen cycle and primary productivity of altered iron inputs from desert dust deposition.

Fine (PM fine) and coarse (PM coarse) particulate matter concentrations and elemental compositions were investigated inside trams during travelling in heating and non-heating seasons. New CAF and older KCSV tramcars were involved in the study. The results obtained for the trams were compared with the outside air quality measured at a nearby urban background site. The coarse (particles with aerodynamic diameter larger than 2.5 µm) and the fine (particles with aerodynamic diameter smaller than 2.5 µm) mass concentrations were determined by gravimetric method. The elemental analysis of the collected samples was carried out by particle induced X-ray emission (PIXE) method at the Institute for Nuclear Research, Hungarian Academy of Sciences (MTA-Atomki) Debrecen, Hungary. The mass concentrations inside the vehicles were 5–20 times higher than in the outdoor air. The elemental composition was similar inside the trams and outdoors in both size fractions. However, some elements (Cr, Zn, Cu) were enriched in the trams and could be derived from outdoor sources such as the re-suspended dust, the rail abrasion, the abrasion of the overhead wire. According to the results the new CAF tram type was less polluted than the old KCSV one. [ABSTRACT FROM AUTHOR]

The properties of the atmospheric aerosols depend on the source region and on the modifications that occur during their transport in the air. We have studied physical and chemical properties of aerosols along with their sink mechanism over two locations in southwest India, an urban site (Pune) and well-established climate observatory at Sinhagad (SINH), which represents rural and high altitude site. The ground-based measurements of aerosols, together with their radiative properties in this study have provided means to understand the observed variability and the impact on the aerosol radiative properties effectively over this region. The annual mean elemental carbon concentration (3.4 µg m− 3) at Pune was observed about three times higher compared to SINH (1.3 µg m− 3), indicating strong emissions of carbon-rich aerosols at the urban location. Aerosol optical properties were derived using the OPAC model which were used to compute the Aerosol radiative forcing (ARF) over both stations calculated using SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model shows pronounced seasonal variations due to changes in aerosol optical depth and single scattering albedo at both locations. The year-round ARF was 4–5 times higher over Pune (31.4 ± 3.5 Wm− 2) compared to SINH (7.2 ± 1.1 Wm− 2). The atmospheric heating rate due to aerosols shows a similar pattern as ARF for these locations. The heating was higher in the wintertime, ~ 0.9–1.6 K day− 1 at Pune, and ~ 0.3–0.6 K day− 1 at SINH. The estimated scavenging ratio was found high for NO3− and Ca.2+. The wet deposition fluxes of Cl−, SO42−, Na+, Mg2+ were observed higher for SINH as compared to Pune, due to the high amount of rain received at SINH. [ABSTRACT FROM AUTHOR]

In-situ knowledge on characteristics of mineral aerosols is important for weather and climate prediction models, particularly for modeling such processes as the entrainment, transport and deposition of aerosols. However, field measurements of the dust emission flux, dust size distribution and its chemical composition under realistic wind conditions remain rare. In this study, we present experimental data over annual expeditions in the arid and semi-arid zones of the Caspian Lowland Desert (Kalmykia, south of Russia); we evaluate characteristics of mineral aerosol concentration and fluxes, estimate its chemical composition and calculate its long-distance transport characteristics. The mass concentration in different years ranges from several tens to several hundred of μg m−3. The significant influence of wind velocity on the value of mass and counting concentration and on the proposed entrainment mechanisms is confirmed. An increased content of anthropogenic elements (S, Sn, Pb, Bi, Mo, Ag, Cd, Hg, etc.), which is characteristic for all observation points in the south of the European Russia, is found. The trajectory analysis show that long-range air particles transport from the Caspian Lowland Desert to the central regions of European Russia tends to increase in the recent decades.

Abstract Air pollution mainly resulting from deforestation and agricultural activities has become one of the major concerns in the Amazonian Basin. A detailed analysis of the PM 10 chemical composition is critical for devising pollution control measures and improving climate models. In this study, daily 24-h filter samples were collected and analyzed in different sites of the Amazon Basin between 2008 and 2016 (over 200 samples). The six sampling sites were classified into two groups, one in South Amazonia, a region with strong influence of land occupation, and another in a remote forest region to the North. The high mean concentrations of PM 10 and the occurrences of extreme events at the Southern site denote air pollution episodes. High correlations between the temporal trends of PM 10 and primary species linked to soil re-suspension and biomass burning highlight the contribution of these sources of air pollution in the region. Significant differences between PM 10 in the South and North regions were observed, for which levels of 72.6 ± 66.5 μg m−3 and 8.9 ± 4.2 μg m−3, respectively. The average concentrations of organic carbon (OC) and elemental carbon (EC) in the aerosol were 5.81 ± 4.18 μg m−3, 2.43 ± 1.65 μg m−3 and 5.17 ± 5.54 μg m−3, 0.51 ± 0.41 μg m−3, respectively, for the Southern and Northern Amazonia sampling sites. The aerosol was largely composed of inorganic species in Southern Amazonia, whose carbonaceous matter accounted for 16% of the gravimetrically measured PM 10. However, in the forest region, the contribution of carbonaceous species, mainly OC, accounted for >90% and remained more constant throughout the seasons. Na+ was the dominant water soluble ion in samples from the Southern region, followed by SO 4 −2, NO 3 −, Ca2+ and K+. High levels of carbonate (CC) were also observed for these samples. For the Northern region, SO 4 −2 was the dominant soluble ion, followed by K+ and NH 4 +. Some of these species exhibited a clear seasonal trend during the study period. This study provides a better understanding of the current state of air pollution in diversified Amazon basin sites. Graphical abstract Unlabelled Image Highlights • Comprehensive assessments of the chemical properties of aerosol particles at two different regions in Amazonia. • Datasets of chemical characteristics of PM10 from a remote forest and from an area on the border between the forest and extensive agricultural areas. • Anthropogenic activities transforming atmospheric composition and affecting air quality and aerosol composition in Amazonian Basin. • Land use activity in South Amazonia reflects in large increase in the re suspension of mineral dust. [ABSTRACT FROM AUTHOR]

Mineral dust composition affects a multitude of processes in the atmosphere and adjacent compartments. Dust dry deposition was collected near source in northwest Africa, in Central Asia, and on Svalbard and at three locations of the African outflow regime. Samples were subjected to automated scanning electron microscopy with energy-dispersive X-ray analysis to obtain size and composition of 216,000 individual particles. Results show low temporal variation in estimated optical properties for each location, but considerable differences between the African, Central Asian, and Arctic regimes. No significant difference was found between the K-feldspar relative abundances, indicating comparable related ice-nucleation abilities. The mixing state between calcium and iron compounds was different for near source and transport regimes, potentially in part due to size sorting effects. As a result, in certain situations (high acid availability, limited time) atmospheric processing of the dust is expected to lead to less increased iron solubility for near-source dusts (in particular for Central Asian ones) than for transported ones (in particular of Sahelian origin).

Atmospheric mercury plays a crucial role in the biogeochemical cycle of mercury. This study conducted an intensive measurement of atmospheric mercury from 2015 to 2018 at a regional site in eastern China. During this period, the concentration of particle-bound mercury (PBM) decreased by 13%, which was much lower than those of gaseous elemenral mercury (GEM, 30%) and reactive gaseous mercury (GOM, 62%). The gradual decrease in the correlation between PBM and CO, K, and Pb indicates that the influence of primary emissions on PBM concentration was weakening. Moreover, the value of the partitioning coefficient (Kp) increased gradually from 0.05 ± 0.076 m 3 /μg in 2015 to 0.16 ± 0.37 m 3 /μg in 2018, indicating that GOM was increasingly inclined to adsorb onto particulate matter. Excluding the influence of meteorological conditions and the primary emissions, the change in aerosol composition is designated as the main trigger factor for the increasing gas-particle partitioning of reactive mercury (RM). The increasing ratio of Cl - , NO 3 - , and organics (Org) in the chemical composition of particle matters (PM 2.5 ), as well as the decrease in the proportion of SO 4 2- , NH 4 + , and K + , are conducive to the adsorption of GOM onto particles, forming PBM, which led to an increase of Kp and a lag of PBM reduction compared to GEM and GOM under the continuous control measures of anthropogenic mercury emissions. The evolution of aerosol compositions in recent years affects the migration and transformation of atmospheric mercury, which in turn can affect the biogeochemical cycle of mercury., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

In order to assess the variability of the chemical composition of atmospheric aerosols in Central Tunisia and determine their origin, 140 aerosols samples were collected from March 2015 to April 2016 in the industrial city of Sfax. The particles collected on membranes were submitted to X-ray Fluorescence analysis and the concentrations of sixteen elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn and Pb) quantified. According to the values of their enrichment factors (EF) relative to the composition of the Earth crust and of sea-salt, these elements can be classified in three main categories: 1) crustal (Al, Si, Fe, Ca, Ti, Ni, P, and Mn), 2) marine (Na, Cl), and 3) anthropogenic (S, Zn, Cu, and Pb). Then, we apply the Positive Matrix Factorization (PMF) to the dataset in order to assess the profiles and contributions of the main sources of the aerosol. Beside the marine and anthropogenic factors, 3 other factors are necessary to represent the mineral dust component, which emphasizes the diversity of its sources. In usual conditions, the dominating factor (Ca-Dust) is enriched in both Ca and Mg, and is most probably emitted from regional sources. Its contribution to the atmospheric aerosol loading usually lies between 0.75 and 6.37μg/m 3 (10th and 90 th percentiles, respectively) but can peak at 9.28μg/m 3 . The second factor, simply referred to as the Dust factor, corresponds to dust emitted by, and transported from, more distant desert sources. During the massive advection events, its contribution to the aerosol loading in Sfax can be above 100μg/m 3 . Finally, the outdoor deposits of the residues of the local phosphate industry are an occasional source of P-enriched mineral dust (P-Dust) and some heavy metals (Cu, Ni, Zn, Pb). However, their contribution to the aerosol concentration is usually low (0.12–0.25μg/m 3 ) and does not seem to constitute an important source of contamination. [ABSTRACT FROM AUTHOR]

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Aerosol pH and aerosol liquid water (ALW) play key roles in regulating many atmospheric processes. In many countries, large reductions in SO 2 and NO x emissions as a result of air pollution regulatory policies have led to improved air quality and significant changes in aerosol mass and chemical composition. Understanding the long-term trends and sensitivities of aerosol pH and ALW to changes in meteorological conditions and chemical composition is useful for predicting how atmospheric processes that depend on aerosol acidity and/or ALW will evolve as air pollutant emissions change over time. At present, long-term monitoring records of aerosol pH and ALW are limited in most parts of China and elsewhere in Asia due to the scarcity of long-term aerosol chemical speciation measurements acquired through regular sampling schedules and consistent analysis protocols in this region. We used a 10-year dataset (2011–2020) from three long-term monitoring sites to investigate the long-term trends of PM 2.5 pH and ALW concentrations, identify key factors that drive the variations of PM 2.5 pH and ALW concentrations, and investigate the sensitivities of PM 2.5 pH and ALW concentrations to chemical composition changes during different seasons in Hong Kong, a highly populated urbanized city located in South China that has experienced improved air quality as a result of various effective air pollution regulatory policies. Despite the substantial decreases in PM 2.5 concentrations and changes in chemical composition in this 10-year period, PM 2.5 pH showed little change. The rates at which PM 2.5 pH and ALW concentration changed ranged from −0.007 to −0.001 pH units/year and from −1.45 to −0.53 μg m−3/year, respectively. Clear and consistent seasonal oscillatory cycles were observed for both PM 2.5 pH (∼2–∼4) and ALW concentrations (∼5–∼40 μg m−3) at the three sites during this 10-year period. PM 2.5 was the most acidic in the fall, and was the least acidic in winter. ALW concentrations were the lowest in summer, and the highest in winter/spring. Sensitivity tests revealed that chemical composition, especially particulate sulfate concentrations, plays a major role in driving the variations in aerosol pH and ALW concentration during each season. However, the magnitudes to which aerosol pH and ALW concentration respond to changes in chemical composition depend strongly on the meteorological conditions in each season. Given that many urbanized cities in South China share similar air quality and meteorological characteristics as Hong Kong, the results presented here are useful for advancing our understanding of how air pollution regulatory policies can alter aerosol pH and ALW concentrations, and consequently aqueous aerosol chemistry, in other South China cities. • Changes in air pollutant emissions did not lead to significant changes in aerosol pH. • Aerosol pH and liquid water had consistent seasonal oscillatory cycles. • Aerosol pH and liquid water response to chemical composition changes depend on the season. • First study on the long-term trends of aerosol pH and liquid water in a South China city. [ABSTRACT FROM AUTHOR]

Comparisons of aerosol composition and sources in different cities or regions are rather limited, yet important for an in-depth understanding of the spatial diversity of aerosol pollution in China. In this study, the data originating from 25 different winter aerosol mass spectrometer (AMS)/aerosol chemical speciation monitor (ACSM) studies were used to provide spatial coverage of the Beijing-Tianjin-Hebei (BTH), Guanzhong (GZ), Yangtze River Delta (YRD), and Pearl River Delta (PRD) regions. The spatial distribution and diurnal variations in aerosol composition and organic sources were analyzed to investigate the aerosol characteristics in the four regions. It was found that there were differences in the compositions of non-refractory particulate matter across the regions, e.g., more sulfate in the PRD versus more nitrate in the YRD, as well as in the organic sources, e.g., more coal combustion in BTH versus more biomass burning in GZ. The characteristics of the composition of NR-PM are similar when the campaigns were classified according to the winter of different years or the cities of different regions. The diurnal variation of the PRD-sulfate indicated its regional nature, whereas the organics from burning sources in two regions of northern China exhibited local characteristics. Based on these findings, we suggest that strict control policies for coal combustion and biomass burning emissions should be enforced in the BTH and GZ regions, respectively.