Non-dust Periods Research Articles

Morphology and chemical composition of mineral particles in a special dust storm with high relative humidity in North China

A special dust storm characterized by high PM10 mass concentrations (921.9 ± 632.3 μg m−3) and high relative humidity (RH; 60.1 % ± 11.1 %) was observed on March 22–24, 2023 at a coastal city of North China. Aerosol particles of PM10 were analyzed by a scanning electron microscope coupled with energy dispersive X-ray and an ion chromatograph. The results showed that individual mineral particles were dominated by clay minerals, followed by quartz, feldspar, and carbonate. Bulk water-soluble inorganic ions analysis showed that SO42- mass concentrations varied from 3.7 μg m−3 to 23.3 μg m−3 with an average value of 12.4 μg m−3. However, their mass ratios to PM10 were relatively stable, being 1.15–2.01 % with an average value of 1.49 % ± 0.25 %, similar to the value near the dust sources (Tengger Desert). Although S-containing individual mineral dust varied from 5.2 % to 70.7 %, the average weight ratio of S on individual mineral dust was 2.1 %, much lower than that of non-dust periods (11.0 %). The results suggested limited sulfate formation on mineral dust surfaces even under high RH. In contrast, NO3-, which was very limited in dust sources, varied from 0.21 % to 4.11 % of the total PM10 with an average value of 1.61 % ± 1.07 %. The research highlighted that nitrate formation has exceeded sulfate formation during severe dust storm episodes, which might because the atmospheric compositions in China have changed significantly with a high mass ratio of NO2/SO2 after the implementation of the strict emission control measures.

Contribution of black carbon and desert dust to aerosol absorption in the atmosphere of the Eastern Arabian Peninsula

Discriminating the absorption coefficients of aerosol mineral dust and black carbon (BC) in different aerosol size fractions is a challenge because of BC's large mass absorption cross-section compared to dust. Ambient aerosol wavelength dependent absorption coefficients (babs) in supermicron and submicron size fractions were determined with a high time resolution. The measurements were performed simultaneously using identical systems at an urban and a regional background site in Qatar. At each site, measurements were taken by co-located Aethalometers, one with a virtual impactor (VI) and the other with a PM1 cyclone to respectively collect super-micron-enhanced and submicron fractions. The combined measurement of aerosol absorption and scattering coefficients enabled the particles to be classified based on their optical properties' wavelength dependence. The classification reveals the presence of BC internally/externally mixed with different aerosols. Helium ion microscopy images provided information concerning the extent of mineral dust in the submicron fraction. The determination of absorption coefficients during dust storms and non-dust periods was used to establish the absorption Ångström exponent for dust and BC. Non-parametric wind regression, potential source contribution function and back-trajectory analysis reveal major regional sources of desert dust associated with north-westerly winds and a minor local dust contribution. In contrast, major BC sources found locally were associated with south-westerly winds with a smaller contribution made by offshore emissions transported by north-easterly and easterly winds. The use of a pair of Aethalometers with VI and PM1 inlets separates contributions of BC and dust to the aerosol absorption coefficient.

Composition and size distribution of wintertime inorganic aerosols at ground and alpine regions of northwest China

Water-soluble inorganic ions (WSIIs) play a pivotal role in atmospheric chemical reactions, particularly influencing the formation of secondary particulate matter. A comprehensive grasp of the vertical distribution of atmospheric pollutants holds immense significance in understanding the diffusion and transportation of these pollutants. This study investigates the WSIIs of PM2.5 and size-segregated particles at the top (∼2060 m a.s.l.) and foot of Mt. Hua during the winter of 2020. All the measured ions present significant higher concentrations (1.9∼6.9 times) at the foot than the top. Cl− and K+ at the foot are more than 4 times of those at the top, whereas Ca2+ and Mg2+ are only 1.3–1.9 times higher. The particle size distribution of NO3−, SO42−, K+ and Cl− demonstrate a single peak distribution (0.7–1.1 µm) at the foot, but with a bimodal distribution (0.7–1.1 µm and 4.7–5.8 µm) at the top. These differences suggest that the aerosol at the alpine region is mainly transported via long-distance from Northwest/North China, but limited influenced by vertical transport through valley breeze. The changes of concentration and size distribution of WSIIs in dust event and non-dust period indicate that the effects of dust event on aerosols at ground surface were weaker than that of the free troposphere of Guanzhong Plain. Notably, our study underscores the dominant influence of NO3− in shaping the gas-particle distribution of ammonia within the winter free troposphere. Our results highlight the significant role of long-range transport on aerosols in the free troposphere in Guanzhong Plain, Northwest China.

Spatiotemporal characteristics and driving mechanisms of PM10 in arid and semi-arid cities of northwest China

PM10 pollution is a pressing ecological concern within arid and semi-arid cities, adversely influencing the natural environment and human health. Based on the Geographically and Temporally Weighted Regression (GTWR) model, this study comparatively investigated the spatiotemporal dynamics of PM10 during non-dust and dust periods in five arid cities (Jiuquan, Jiayuguan, Zhangye, Jinchang, and Wuwei) and one semi-arid city (Lanzhou) in northwest China. Further, this study examined the critical mechanisms of PM10 via the GTWR and Geographic Detector model. A comparative analysis illustrated that dust period PM10 concentrations surpassed non-dust period concentrations. The annual average PM10 concentrations during the non-dust period wavily declined from 2015 to 2020, exhibiting significantly higher levels in the semi-arid city as opposed to arid cities. Conversely, during the dust period, PM10 levels rose initially between 2015 and 2017 and diminished from 2018 to 2020, with high concentration clusterings primarily observed in 2015–2016 in western arid cities, Jiuquan and Jiayuguan, in 2017–2019 in eastern cities, Wuwei and Lanzhou, and in 2020 in central arid cities, Jinchang and Zhangye. During the non-dust period from 2015 to 2020, the cumulative effects of single driving factors were ranked in the following order: soil moisture content (MOI), geographical location (LOC), precipitation (PRE), SO2, gross domestic product (GDP), wind speed (WS), and digital elevation (DEM) while during the dust period, the emphasized factors were ranked in the following order: MOI, LOC, PRE, WS, SO2, GDP, and DEM. The interaction between MOI and WS on PM10 was most noticeable in this study (non-dust: 0.787, dust: 0.832). Thus, MOI and WS are critical components in controlling PM10 pollution. The outcomes of this study can furnish theoretical foundations for ecological construction in Northwest China, unlock novel insights for ecological measures in other global arid and semi-arid cities.

Modification of Saharan dust size distribution during its transport over the Anatolian Plateau

Particle number size distribution in dust plumes and its modification as the plume travels over the Anatolia were investigated by measuring particle number size distributions at two stations: one located on the Mediterranean coast of Turkey and the other on the Anatolian plateau. Clustering of backtrajectories revealed six trajectory clusters at the Marmaris station and nine clusters at the Ankara station. Cluster 6 in Marmaris and clusters 6, 7 and 9 in Ankara stations had the potential to transport Saharan dust to stations. Concentration of particles with D ≤ 1 μm increased during dust events in the Ankara station, but decreased at the Marmaris station. Higher PM1 concentrations during the non-dust period at the Marmaris station were attributed to the dominance of secondary particle formation on PM1 concentrations. Occurrence of sea salt episodes at the Marmaris station and anthropogenic episodes at the Ankara station affects the distribution of episodes. If different types of episodes are not differentiated and all episodes are considered as dust, it can lead to misleadingly high dust episodes in winter. Six Saharan dust episodes were sequentially intercepted first at the Marmaris and then at the Ankara stations. These episodes were used to study how dust size distribution is modified as the plume travels from the Mediterranean coast to central Anatolia. On the average, travel time between the two stations is 1–2 days. Particle number concentrations in 1 μm ≤ D ≤ 110 μm size range were consistently high at the Ankara station, indicating that local sources play a role in modifying the number size distribution as the plume travels over the Anatolian plateau.

Seasonal variations, source apportionment and dry deposition of chemical species of total suspended particulate in Pengjia Yu Island, East China Sea

Total of 172 total suspended particulate (TSP) samples and its chemical compositions were collected and analyzed from January to December 2010 in Pengjia Yu Island, an open region in East China Sea (ECS). Despite the predominance of sea-salt major ions (Na+, Cl−), the presence of non-sea-salt SO42− (nss-SO42−) and NO3− as well as combustion-derived trace metals clearly establishes the impact of anthropogenic sources over ECS. The annual contributions of coal, heavy-fuel oil and traffic to the measured chemical species were 21.0 %, 15.0 % and 15.5 %, respectively. Especially in spring, the contributions of crustal minerals to measured chemical species during dust period (33.6 %) were higher than that (13.2 %) during non-dust period. The calculated annual average dry deposition fluxes for trace metals and total inorganic nitrogen were 246.1 ± 345.8 μg/m2/d and 2950.4 ± 2245.0 μg/m2/d, suggesting that atmospheric deposition is an important source of nutrient elements for the south of ECS.

Abrupt High PM Concentration in an Urban Calm Cavity Generated by Internal Gravity Waves and a Shallow Coastal Atmospheric Boundary Layer with the Influence of the Yellow Dust from China

Using GRIMM-1107 aerosol sampler, GOES-9 DCD satellite images, HYSPLIT model of backward trajectory and 3D-meteorological WRF-3.6 model, high particulate matter concentrations were investigated at Gangneung city in the Korean east coast which consists of Mt. Taeglyung in its west and the East Sea in its east on 00:00LST March 26~00:00 LST 4 April 2004. During a Yellow Dust period, the maximum PM10 (PM2.5 and PM1) concentration at the city was about 3.3 (1.1 and 1.01) times higher than one in the non-dust period. After the transported dust from the Gobi Desert and Nei-Mongo by strong northwesterly wind passed over Mt. Taegulyang and moved down toward the city. Then the dust was trapped inside a calm cavity generated by the confront of internal gravity waves (IGW) over the city and the eastward movement of the trapped dust is prohibited by the easterly onshore wind from the East Sea, and the trapped dust further combined with particulate and gaseous emitted from the road vehicles and heating boilers of the city at 09:00LST, March 30 (beginning time of office hours), causing high PM concentrations. On mid-day, as the combined dust due to daytime sufficient thermal convection rises up to the top of the thermal internal boundary layer (TIBL) of a 300 m depth from the coast to the top of the mountain, the ground-based PM concentrations in the city are much lower at 15:00LST due to the higher thickness of the TIBL than at 09:00LST. At night, particulates emitted from many road vehicles after the end of office hours and residential heating boilers could combine with both dust transported from the Nei-Mongo and falling dust uplifted from the ground surface of the city during the day, and they were trapped inside a calm cavity by the IGV under much shallower stable nocturnal surface inversion layer than the TIBL, causing more dust to be accumulated near the surface and showing the maximum PM concentrations at 20:00 LST.

Impacts of dust events on chemical characterization and associated source contributions of atmospheric particulate matter in northern China

Sand and dust have significant impacts on air quality, climate, and human health. To investigate the influences of dust storms on chemical characterization and source contributions of fine particulate matter (PM2.5) in areas with different distances from dust source regions, PM2.5 and associated chemical composition were measured in two industrial cities with one near sand sources (i.e., Wuhai) and the other far from sand sources (i.e., Jinan) in northern China in March 2021. Results showed that PM mass concentrations significantly increased and exceeded the Chinese National Ambient Air Quality standard during the dust events, with absolute concentrations and fractional contributions of PM2.5-bound crustal and trace elements increased while secondary inorganic ions decreased at both sites. Crustal materials dominated the increased PM2.5 mass from non-dust period to dust period in both cities. These were further evidenced by PM2.5 source apportionment results from positive matrix factorization model. During the dust events, dust sources contributed up to 88% of PM2.5 mass in Wuhai and ∼38% of PM2.5 mass in Jinan, a city about thousands of kilometers away from the sand source. Besides, the measurement data indicated that dust from northwest China may also bring along with high abundance of organic matter and vanadium. Secondary and traffic sources were two of the most important source contributors to PM2.5 in both cities during the non-dust periods. However, the near sand source city was more susceptible to the aggravating effects of dust and minerals, with much higher contributions by crustal materials (∼47%, from the aspect of chemical components) and dust-related sources (∼26%, from the aspect of sources) to PM2.5 mass even during non-dust periods. This study highlighted the urgent need for more action and effective control of sand sources to reduce the impact on air quality in downstream regions.

Oxidative potential of size-segregated particulate matter in the dust-storm impacted Hotan, northwest China

Reactive oxygen species (ROS) induced by particulate matter (PM), of which •OH is the most active free radical, have adverse health effects; however, PM-induced generation of ROS and •OH has not been quantified and studied in northwest China, which suffers from severe dust storms. In this study, ambient PM10 and PM2.5 collected from the urban area of Hotan in the Uygur Autonomous Region of China, during dust and non-sand periods in 2020. ROS and •OH were quantified and examined using the dichlorofluorescein diacetate (DCFH) assay and fluorescent probe method. The results showed that the oxidation potential (OP) of PM in the non-dust period (PM2.5: 7.77 ± 0.29 nmol H2O2 m−3; PM10: 8.9 ± 0.38 nmol H2O2 m−3) was higher than in the dust period (PM2.5: 1.14 ± 0.71 nmol H2O2 m−3; PM10: 1.85 ± 0.77 nmol H2O2 m−3). Compared to PM10, PM2.5 with larger specific surface area is more likely to adsorb the components contributing to ROS generation, so the induction amount of ROS and •OH per unit volume in the environment will increase with increasing PM2.5 concentration. There was a weak correlation between O3 and ROS concentrations in the PM during the day, suggesting that photochemical reactions were a moderating factor in the formation of daytime ROS. In PM2.5, ROS showed a weak correlation with Pb, Cu, and Fe during the dust period. During the non-dust period, significantly correlated with Fe, Cu, and Cd (P < 0.01; P < 0.05). In PM10, ROS correlated significantly with As (P < 0.05) but weakly with Fe and Pb during the dust period. During the non-dust period, significantly correlated with As and Cd (P < 0.01; P < 0.05) and weakly correlated with Ni, Cu, and Fe. This indicates that increasing trace metal levels can increase the OP of atmospheric PM.

Respiratory and cardiovascular effects of ambient particulate matter from dust storm and non-dust storm periods in Kuwait

Epidemiological studies demonstrate a positive association between daily changes in concentrations of ambient airborne particulate matter (PM) and adverse respiratory and cardiovascular health effects. However, physicochemical properties of PM can vary greatly across geographical, atmospheric, and temporal conditions and influence the relative toxicity of airborne PM. The purpose of this study was to investigate the adverse pulmonary and cardiovascular health effects of ambient PM collected from discrete sampling sites in Kuwait during dust storm (DS) and non-dust storm (NDS) conditions. Collected dust samples were characterized for their chemical composition using atomic absorption, GC–MS, and HPLC–MS analyses. Male BALB/cJ mice were exposed to 100 µg of either NDS or dust storm (DS) PM in 50 µl of PBS by oropharyngeal aspiration. Lung function was measured and bronchoalveolar lavage was conducted at 1, 7, and 14 days post-exposure. Ischemia–reperfusion injury was performed 24 h after exposures by obstructing the left main coronary artery approximately 4 mm distal to its origin for 20 min, followed by 2 h. of reperfusion. Exposure to either NDS or DS PM resulted in airway hyperresponsiveness to acetylcholine compared to PBS controls. Total protein and cells in BAL fluid were elevated in both dust groups one day after exposure; however, DS PM induced a greater increase in cell numbers than did NDS PM, particularly in neutrophils, eosinophils, and lymphocytes. Representative lung sections exhibited positive staining for mucus in large airways at 7 days which resolved by 14 days in dust storm-exposed mice but persisted in NDS-exposed animals. Our findings suggest that NDS PM may be more effective in producing an adaptive immune response, while the early inflammation induced by DS PM may better resolve. We also observed a prolonged airway mucus response after exposure to NDS PM, suggesting it may produce more asthma-like features than dust storm PM. PM-induced changes to cardiac ischemia–reperfusion injury were not observed in this study. The lack of cardiovascular response may have been due to the limited exposure and single time point used in this study.

Distribution and sources of PM2.5-bound free silica in the atmosphere of hyper-arid regions in Hotan, North-West China

The composition of atmospheric fine particulate matter (PM2.5) is complex and exhibits strong regional differences. Free silica (α-SiO2) in atmospheric particulate matter is carcinogenic and is an important component of respirable particulate matter in urban areas. Measurements determined that the concentration of silicon dioxide (α-SiO2) in PM2.5 in the urban area of Hotan City, China, was 8.02 μg·m−3 during the dust period and exceeded 1.77 μg·m−3 during the non-dust period. The proportion of α-SiO2 in PM2.5 was 8.07% during the dust period and 2.25% during the non-dust period. Atmospheric visibility during the dust period was mainly influenced by the content of atmospheric floating dust. Analysis of α-SiO2 pollution sources during the dust period showed that the air masses containing sand and dust originated from the desert hinterland. Following passage through oasis areas, the air mass was effectively reduced in the concentration of α-SiO2 in PM2.5. During the dusty period, α-SiO2 and PM2.5 originated from the same source in Hotan City. Moreover, wind speed was the main influencing factor for the α-SiO2 concentration. During the non-dust period, α-SiO2 and PM2.5 were not from the same source of pollution.

Mechanisms underlying the health effects of desert sand dust.

Desertification and climate change indicate a future expansion of the global area of dry land and an increase in the risk of drought. Humans may therefore be at an ever-increasing risk of frequent exposure to, and resultant adverse health effects of desert sand dust. This review appraises a total of 52 experimental studies that have sought to identify mechanisms and intermediate endpoints underlying epidemiological evidence of an impact of desert dust on cardiovascular and respiratory health. Toxicological studies, in main using doses that reflect or at least approach real world exposures during a dust event, have demonstrated that virgin sand dust particles and dust storm particles sampled at remote locations away from the source induce inflammatory lung injury and aggravate allergen-induced nasal and pulmonary eosinophilia. Effects are orchestrated by cytokines, chemokines and antigen-specific immunoglobulin potentially via toll-like receptor/myeloid differentiation factor signaling pathways. Findings suggest that in addition to involvement of adhered chemical and biological pollutants, mineralogical components may also be implicated in the pathogenesis of human respiratory disorders during a dust event. Whilst comparisons with urban particulate matter less than 2.5μm in diameter (PM2.5) suggest that allergic inflammatory responses are greater for microbial element-rich dust- PM2.5, aerosols generated during dust events appear to have a lower oxidative potential compared to combustion-generated PM2.5 sampled during non-dust periods. In vitro findings suggest that the significant amounts of suspended desert dust during storm periods may provide a platform to intermix with chemicals on its surfaces, thereby increasing the bioreactivity of PM2.5 during dust storm episodes, and that mineral dust surface reactions are an unrecognized source of toxic organic chemicals in the atmosphere, enhancing toxicity of aerosols in urban environments. In summary, the experimental research on desert dust on respiratory endpoints go some way in clarifying the mechanistic effects of atmospheric desert dust on the upper and lower human respiratory system. In doing so, they provide support for biological plausibility of epidemiological associations between this particulate air pollutant and events including exacerbation of asthma, hospitalization for respiratory infections and seasonal allergic rhinitis.

Water-soluble brown carbon in atmospheric aerosols along the transport pathway of Asian dust: Optical properties, chemical compositions, and potential sources

As an important type of light-absorbing aerosol, brown carbon (BrC) has the potential to affect the atmospheric photochemistry and Earth's energy budget. A comprehensive field campaign was carried out along the transport pathway of Asian dust during the spring of 2016, including a desert site (Erenhot), a rural site (Zhangbei), and an urban site (Jinan), in northern China. Optical properties, bulk chemical compositions, and potential sources of water-soluble brown carbon (WS-BrC) were investigated in atmospheric total suspended particulate (TSP) samples. Samples from Zhangbei had higher mass absorption efficiency at 365 nm (MAE365, 1.32 ± 0.34 m2 g−1) than those from Jinan (1.00 ± 0.23 m2 g−1) and Erenhot (0.84 ± 0.30 m2 g−1). Compere to the non-dust samples, elevated water-soluble organic carbon (WSOC) concentrations and MAE365 values of dust samples from Erenhot are related to the input of high molecular weight organic compounds and biogenic matter from the Gobi Desert, while lower values from Zhangbei and Jinan are attributed to the dilution effect caused by strong northwesterly winds. Based on fluorescence excitation–emission matrix spectra and parallel factor analysis, two humic-like (C1 and C2) and two protein-like (C3 and C4) substances were identified. Together, C1 and C2 accounted for ~64% of total fluorescence intensity at the highly polluted urban Jinan site; C3 represented ~45% at the rural Zhangbei site where local biomass burning affects; and C4 contributed ~24% in the desert region (Erenhot) due to dust-sourced biogenic substances. The relative absorptive forcing of WS-BrC compared to black carbon at 300–400 nm was about 31.3%, 13.9%, and 9.2% during non-dust periods at Erenhot, Zhangbei, and Jinan, respectively, highlighting that WS-BrC may significantly affect the radiative balance of Earth's climate system and should be included in radiative forcing models.

Time-Determination and Contribution Analysis of Transport, Retention, and Offshore Backflow to Long-Term Sand-Dust Coupling

Continuous on-line observation of particulate matter and PM2.5 chemical composition was conducted from October 15th to November 7th 2019 in East China. During the observation period, a wide range of dust-related processes took place. According to supplementary urban air quality assessment affected by dust (hereafter referred to as supplementary provisions), the observations were divided into four stages including pre-dust event, dust Ⅰ, dust Ⅱ, and post-dust event. The dust Ⅰ stage represented the processes of transportation and retention, while the dust Ⅱ stage represented processes of backflow from the sea and scavenging. The start time of the studied dust event was October 29th 08:00-09:00 based on the supplementary provisions, dust tracers, and air quality models; however, disagreements existed between these data sources with respect to the finishing time. The supplementary provisions could not effectively distinguish backflow dust from sea, and results from different dust tracers were variable. The WRF-CMAQ model simulated dust variation trends well but overestimated short-term suspended dust and backflow dust. PM10, PM2.5, and trace element concentrations were much higher during dust events than during non-dust periods, with highest daily concentrations of (234.8±125.5), (76.8±22.5), and (17.54±10.5) μg·m-3, respectively, which occurred on October 29th. During the dust event, concentration of crustal elements were remarkably high in PM2.5. At the same time, secondary ions (SO42-, NO3-, and NH4+) contributed less to PM2.5 mass concentrations. Four major crustal elements (Al, Si, Ca, and Fe) accounted for 23.5% and 13.7% of the mass concentration of PM2.5 and secondary ions accounted for 24.3% and 41.9% during dust Ⅰ and dust Ⅱ stages, respectively. Based on PMF source apportionment, Ca abundance, PM2.5/PM10 in dust sources, and the reconstruction of crustal material, dust particulates accounted for 43.4%-50.0% of PM2.5 and backflow dust accounted for 19.2%-24.7% of PM2.5.

Records of Inorganic Ions and Dust Particles in Snow at Yushugou Glacier No. 6 in the Desert Belt of Northwestern China

Chemical ions and dust particles deposited in snow can be used as indicators of climatic and environmental processes. Understanding their sources, energy transfer and evolutionary mechanisms is extremely important in tracking regional climate and environmental changes. We collected snow samples from three pits at different altitudes and from the surface of Yushugou Glacier No. 6, Tianshan Mountains, China, in the summers of 2017 and 2018. Sea-salt tracing, correlation analysis and factor analysis were used to determine the characteristics and sources of the major ions and mineral dust particles in the snow. We found obvious seasonal variations, with high concentrations of dust particles and major ions deposited during the dust period, and relatively low concentrations deposited during the non-dust period. The concentrations peaked within two distinct dust layers in the snow pits. There was a significant correlation between the peak values and the dust layer. The ionic concentrations were ranked from highest to lowest as Ca2+ > SO42- > Cl- > Na+ > NO3- > NH4+ > Mg2+ > K+. Therefore, SO42- was the dominate anion and Ca2+ was the dominate cation. The major ions in the snow at Yushugou Glacier No. 6 are mainly derived from terrestrial mineral dust but also include limited inputs from human activities and sea salt.

Seasonal behavior of water-soluble organic nitrogen in fine particulate matter (PM2.5) at urban coastal environments in Hong Kong

Water-soluble organic nitrogen (WSON) in fine particulate matter (PM2.5) was determined at urban coastal environments in China based on 1-year measurement. The WSON concentrations were in a range of 14.3–257.6 nmol N m−3 and accounted for 22.0–61.2% of the water-soluble nitrogen (WSN) in composition. The average total concentration of free amino acid (FAA) was 1264.5 ± 393.0 pmol m−3, which was lower than those in continental urban cities but nevertheless comparable to the rural area of Pearl River Delta (PRD) in China. The total quantified amines and amino compounds ranged from 223.8 to 806.0 pmol m−3 in which methylamine, ethylamine, and ethanolamine were the most abundant compounds. The average concentration of urea was 7.8 ± 3.0 nmol m−3 and at least one order of magnitude higher than those in marine and rural areas but comparable to other continental cities in China during non-dust period. Summer showed the highest average concentration of WSON (95.0 ± 66.6 nmol N m−3) and composition in WSN (49.3%) compared to other seasons (27.9–37.0%). The results were consistent with previous findings that the inorganics can contribute more than the organics in secondary aerosol formation. There were no distinctive seasonal variations of organic compositions of FAA, amine and amino compounds, and urea. This observation was possibly attributed to a mix of original sources in urban and different prevailing wind directions. Fair correlations (r < 0.4) between WSON compounds and atmospheric oxidants [ozone (O3) and nitrogen oxides (NOx)] suggest that biogenic oxidation is possibly not a major contributing factor in atmospheric coastal urban location.

Analysis of Different Particle Sizes, Pollution Characteristics, and Sources of Atmospheric Aerosols During the Spring Dust Period in Beijing

To understand the evolution of the physical and chemical properties of dust aerosols in the atmosphere, the concentrations and chemical compositions of differently sized particles were continuously observed and analyzed using an ion chromatograph and carbonaceous analyzer during the outbreak of dust in May 2017 in Beijing. The concentrations of total suspended particulate (TSP), water-soluble organic carbon (WSOC), elemental carbon (EC), OC, and water-soluble inorganic ions were (2237.59±681.49), (29.90±18.05), (1.46±3.05), (67.35±29.07), and (136.75±46.38) μg·m-3 during the dust period, respectively, and significantly exceeded that of the non-dust period, except for EC. The Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3-, SO42-, and WSOC concentrations during the dust storm period were 11.55, 3.00, 14.88, 14.89, 9.40, 4.60, 2.40, 3.91, and 1.83 times higher than that during the non-dust period. The growth of crustal ions, such as Ca2+ and K+, was notably the largest and NH4+ and NO3- were minimal. The size distribution indicates that crustal ions primarily occur in the coarse mode during the whole sampling campaign. The SO42- and NO3- ions are slightly bimodal during the dust storm, with a dominant peak in the coarse mode at 4.7-5.8 μm and a very minor peak in the fine mode with a size range of 0.43-0.65 μm. During the non-dust period, SO42- is the dominant mode in the fine mode, while NO3- changes little compared with that during the dust period, which indicates that heterogeneous reaction with crustal ions is the main formation mechanism of NO3- in the coarse mode. A significant positive correlation was observed between SO42- and the sum of crustal ions during the dust period, indicating that the source of SO42- during the dust period is remote transmission of the dust storm. During the non-dust period, the positive correlation of SO42- with NH4+ indicates that secondary formation is the main source of SO42-. Based on correlation analysis of NO3- with crustal ions and NH4+, both remote transmission and secondary formation are the sources of NO3- during the dust storm and heterogeneous reactions are predominant during the non-dust period.

Chemical characteristics of airborne particles in Xi'an, inland China during dust storm episodes: Implications for heterogeneous formation of ammonium nitrate and enhancement of N-deposition

To identify the sources and heterogeneous reactions of sulfate and nitrate with dust in the atmosphere, airborne particles in Xi'an, inland China during the spring of 2017 were collected and measured for chemical compositions, along with a laboratory simulation of the heterogeneous formation of ammonium nitrate on the dust surface. Our results showed that concentrations of Ca2+, Na+ and Cl− in the TSP samples were enhanced in the dust events, with the values of 41.8, 5.4 and 4.0 μg m−3, respectively, while NO3− (7.1 μg m−3) and NH4+ (2.4 μg m−3) remarkably decreased, compared to those in the non-dust periods. During the dust events, NH4+ correlated only with NO3− (R2 = 0.52) and abundantly occurred in the coarse mode (>2.1 μm), in contrast to that in the non-dust periods, which well correlated with sulfate and nitrate and enriched in the fine mode (<2.1 μm). SO42− in Xi'an during the dust events existed mostly as gypsum (CaSO4·2H2O) and mirabilite (Na2SO4·10H2O) and dominated in the coarse mode, suggesting that they were directly transported from the upwind Gobi Desert region. Our laboratory simulation results showed that during the long-range transport hygroscopic salts in the Gobi dust such as mirabilite can absorb water vapor and form a liquid phase on the particle surface, then gaseous NH3 and HNO3 partition into the aqueous phase and form NH4NO3, resulting in the strong correlation of NH4+ with NO3− and their accumulation on dust particles. The dry deposition flux of total inorganic nitrogen (NH4+ + NO3−) in Xi'an during the dust events was 0.97 mg-N m−2 d−1 and 37% higher than that in the non-dust periods. Such a significant enhanced N-deposition is ascribed to the heterogeneous formation of NH4NO3 on the dust particle surface, which has been ignored and should be included in future model simulations.

Pollution characteristics in a dusty season based on highly time-resolved online measurements in northwest China

To investigate the pollution characteristics and potential sources in a dusty season, an online analyzer was used to measure trace gases and major water-soluble ions in PM10 from April 1st to May 29th, 2011 in Lanzhou. The average concentrations of HONO, HNO3, HCl, SO2 and NH3 were 0.93, 1.16, 0.48, 9.29 and 5.54 μg/m3, respectively, and 2.8, 2.76, 8.28 and 2.48 μg/m3 for Cl−, NO3−, SO42− and NH4+. In the non-dust period, diurnal variations of SO42−, NO3− and their gaseous precursors showed similar change trend. NH4+ showed unimodal pattern whereas NH3 illustrated a bimodal pattern. HCl and Cl− showed an opposite diurnal pattern. In the dust event, temporal profiles of HCl and Cl−, SO2 and SO42− all presented similar change trend, and SO42− and Cl− preceded dust ions (Ca2+ and Mg2+) 13 h. The ratios of NO3− to SO42− were 0.65 in the non-dust period and 0.31 in the dust event. In the dust event, the sulfur oxidation ratio (SOR) was a factor of 1.33 greater than that in the non-dust period, and [SO42−]/[SO2] was 2.31 times of that in the non-dust period. The source apportionment using Probabilistic Matrix Factorization (PMF) suggested that fugitive dust (58.09%), secondary aerosols (33.98%), and biomass burning (7.93%) were the major sources in the non-dust period whereas dust (67.01%), salt lake (29.68%), biomass burning (0.8%), and motor vehicle (2.51%) were the primary sources in the dust event. Concentration weighted trajectory (CWT) model indicated that NO3−, Cl− and K+ could be regarded as local source species, the potential sources of Na+, Mg2+ and Ca2+ concentrated in the two large areas with the one covered in the junction areas of Xinjiang, Qinghai and Gansu and another one covered the places around in Lanzhou, the potential sources of SO42− were mainly localized in the areas adjacent to Lanzhou.

Aerosol optical absorption coefficients at a rural site in Northwest China: The great contribution of dust particles

An intensive measurement campaign was conducted at a rural site in Northwest China to investigate aerosol optical absorption properties, using the ground-based mobile facility of the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). The average mass concentration of PM2.5 was 103 ± 4 μg m−3 during the 20-day campaign in April 2014. Black carbon (BC) only accounted for ∼0.4% of the PM2.5 on average, with the mean concentration of 443 ± 12 ng m−3 measured using a single particle soot photometer (SP2). The aerosol absorption coefficient (σap) was 5.69 ± 0.01 Mm−1 on average, recorded by a multi-angle absorption photometer (MAAP) at the wavelength of 637 nm. It showed a linear relationship with BC mass concentration during non-dust periods, especially at their diurnal peaks of 07:00–09:00 a.m. (local standard time), deriving a bulk mass absorption efficiency (MAE) for BC of 8.5 ± 1.1 m2 g−1. The σap increased sharply during the dust storm, while the BC remained at a lower concentration than other moments, implying that the dust particles had a considerable contribution to light absorption. On average, dust particles accounted for 26.7% of the aerosol absorption and increased to 71.6% during the dust storm. The MAE of dust was calculated to be 0.014 ± 0.00028 m2 g−1, which was comparable to that measured in the downwind regions in East Asia. Based on the Mie theory for spherical particles, the refractive index (m) of natural mineral dust particles was estimated to be 1.50–0.0007i in Northwest China.