Impact of sand and dust storms on the atmospheric environment and its source in Tianjin-China

Atmospheric environment characteristic of severe dust storms and its impact on sulfate formation in downstream city

This study comprehensively investigated the impact of dust storms (DSs) on downstream cities, by selecting representative DS events. In this paper, we discussed the characteristics of meteorological conditions, air pollutants, PM2.5 components, and their influence on sulfate formation mechanisms. During DSs, strong winds, reaching speeds of up to 10 m/s, led to significant increases in PM10 and PM2.5, with maximum concentrations of 2684.5 and 429 μg/m3, respectively. Primary gaseous pollutants experienced substantial reductions, with decline rates of 48.1, 34.9, 36.8, and 9.0 % for SO2, NO2, NH3, and CO, respectively. Despite a notable increase in PM2.5 concentrations, only 7.6 % of the total mass of PM2.5 was attributed to ionic and carbonaceous components, a much lower value than observed before the DSs (77.3 %). Concentrations of Fe, Ti, and Mn exhibited increases by factors of 6.5-14.1, 10.4-17.0, and 1.6-4.7, respectively. In contrast to the significant decrease of >76.2 % in nitrogen oxidation ratio (NOR), sulfur oxidation ratio (SOR) remained at a relatively high level, displaying a strong positive correlation with high concentrations of Fe, Mn, and Ti. Quantitative analysis revealed an average increase of 0.187 and 0.045 μg/m3 in sulfate from natural sources and heterogeneous generation, respectively. The heterogeneous reaction on mineral dust was closely linked to atmospheric humidity, radiation intensity, the form of metal existence, and concentrations of it. High concentrations of titanium dioxide and iron‑manganese oxides in mineral dust promoted heterogeneous oxidation of SO2 through photocatalysis during the daytime and metal ion catalysis during the nighttime. This study establishes that the metal components in mineral dust promote heterogeneous sulfate formation, quantifies the yield of sulfate generated as a result, and provides possible mechanisms for heterogeneous sulfate formation.

Changes of water-soluble inorganic sulfate and nitrate during severe dust storm episodes in a coastal city of North China

Dust storms are one of the largest sources of non-exhaust emissions in China, which can adversely affect air quality and human health during long-distance transportation. To study the influence of dust storms on aerosol particle composition, samples of fine aerosol (PM2.5) were collected before, during, and after the severe dust storm episodes in a coastal city of North China. Then the water-soluble inorganic ions in the filters were analyzed. The results showed that the chemical composition varied significantly in different sampling periods. Before the dust storm periods (Phase 1), the weather was characterized by high relative humidity. NO3- was the main water-soluble inorganic ion, accounting for about 1/3 of the total mass of PM2.5, which is very different from the situation a few years ago when sulfate was the dominant. The results indicated that the chemical composition of the atmosphere in China has changed significantly after the implementation of strict air pollution control measures. During the severe dust storm periods (within a few hours after the dust invasion, Phase 2), the proportion of Ca2+ in PM2.5 was high; the sulfate formation was limited due to adiabatic air mass affected by the cold front, and the sulfate content might be mainly from desert soil. However, a small amount of nitrate can be formed during their long-distance transportation. After the dust storm periods (Phase 3), dust plums and local polluted air mass mixed well. The proportion of secondary inorganic ions increased, and nitrate formation was still the main. The changes in the chemical composition from a few years ago during Phase 1 and the sharp changes in different water-soluble inorganic ions during different Phases should be carefully considered to evaluate their implications for air quality and human health.

Variations of PM2.5-bound elements and their associated effects during long-distance transport of dust storms: Insights from multi-sites observations

Dust storms are a significant concern because of their adverse effects on ambient air quality and human health. To investigate the evolution of dust storms during long-distance transport and its impacts on air quality and human health risks in cities along the transport pathway, we monitored the major fraction of dust (i.e., particle-bound elements) online in four cities in northern China during March 2021. Three dust events originating from the Gobi Desert of North China and Mongolia and the Taklimakan Desert of Northwest China were captured. We investigated the source regions of dust storms using daily multi-sensor absorbing aerosol index products, backward trajectories, and specific element ratios, identified and quantified sources of particle-bound elements using Positive Matrix Factorization model, and calculated the carcinogenic and non-carcinogenic risks of elements using a health risk assessment model. Our results indicated that under the influence of dust storms, mass concentrations of crustal elements increased up to dozens of times in cities near the dust source and up to ten times in cities farther from the source. In contrast, anthropogenic elements increased less or even decreased, depending on the relative contributions of the increase caused by accumulation of dust itself and entrainment along the transport path and the decrease caused by dilution of high wind speeds. Si/Fe ratio was found to be a valuable indicator for characterizing the attenuation of the amount of dust along its transport pathways, especially for the case originated from northern source regions. This study highlights the significant role of source regions, intensity and attenuation rates of dust storms, and wind speeds in determining the increased levels of element concentrations during dust storms and its associated impacts on downwind areas. Furthermore, non-carcinogenic risks of particle-bound elements increased at all sites during dust events, emphasizing the importance of personal exposure protection during dust storms.

Variations of inhalation risks during different heavy pollution episodes based on 3-year measurement of toxic components in size-segregated particles

Toxic metals (TMs) and polycyclic aromatic hydrocarbons (PAHs) in size-segregated particles during common days (CD) and different heavy pollution (HP) episodes were measured during 2018-2021 in a Chinese megacity. The Multiple Path Particle Dosimetry Model (MPPD) was performed to estimate deposition efficiency, and then inhalation risks in the human pulmonary region during different types of HP were assessed and compared. The higher pulmonary deposition efficiency of PAHs and TMs during all types of HP than those during CD was confirmed. The accumulative incremental lifetime cancer risk (ILCR) of different HP were 2.42 × 10^-5, 1.52 × 10^-5, 1.39 × 10^-5, 1.30 × 10^-5 and 2.94 × 10^-6 for HP4 (combustion sources HP), HP1 (ammonium nitrate HP), HP5 (mixed sources HP), HP3 (resuspended dust HP) and HP2 (ammonium sulfate HP), respectively. The accumulative hazard quotient (HQ) during different HP episodes decreased in the order of HP4 (0.32) > HP3 (0.24) > HP1 (0.22) > HP5 (0.18) > HP2 (0.05). The inhalation risks were dominated by Ni and Cr, what's more, the HQ of Ni and ILCR of Cr during the five HP episodes shared a similar size distribution pattern. However, the characteristic components during different HP episodes and their size distributions of them were distinctive. The size distribution of inhalation risks of the related components (Ni, Cr, BaP, and As) from the combustion process during HP4 peaked at fine mode (0.65-2.1 μm). The size distribution of inhalation risks of the dust-related components (Mn and V) and the components (As and BaP) that are likely to volatilize and re-distribution peaked at coarse mode (2.1-3.3 μm) during HP3. Notably, Mn and Co as catalysts at fine mode could increase the degree of secondary formation and toxicity.

Trends of source apportioned PM2.5 in Tianjin over 2013-2019: Impacts of Clean Air Actions

A long-term (2013-2019) PM_2.5 speciation dataset measured in Tianjin, the largest industrial city in northern China, was analyzed with dispersion normalized positive matrix factorization (DN-PMF). The trends of source apportioned PM_2.5 were used to assess the effectiveness of source-specific control policies and measures in support of the two China's Clean Air Actions implemented nationwide in 2013-2017 and 2018-2020, respectively. Eight sources were resolved from the DN-PMF analysis: coal combustion (CC), biomass burning (BB), vehicular emissions, dust, steelmaking and galvanizing emissions, a mixed sulfate-rich factor and secondary nitrate. After adjustment for meteorological fluctuations, a substantial improvement in PM_2.5 air quality was observed in Tianjin with decreases in PM_2.5 at an annual rate of 6.6%/y. PM_2.5 from CC decreased by 4.1%/y. The reductions in SO₂ concentration, PM_2.5 contributed by CC, and sulfate demonstrated the improved control of CC-related emissions and fuel quality. Policies aimed at eliminating winter-heating pollution have had substantial success as shown by reduced heating-related SO₂, CC, and sulfate from 2013 to 2019. The two industrial source types showed sharp drops after the 2013 mandated controls went into effect to phaseout outdated iron/steel production and enforce tighter emission standards for these industries. BB reduced significantly by 2016 and remained low due to the no open field burning policy. Vehicular emissions and road/soil dust declined over the Action's first phase followed by positive upward trends, showing that further emission controls are needed. Nitrate concentrations remained constant although NO_X emissions dropped significantly. The lack of a decrease in nitrate may result from increased ammonia emissions from enhanced vehicular NO_X controls. The port and shipping emissions were evident implying their impacts on coastal air quality. These results affirm the effectiveness of the Clean Air Actions in reducing primary anthropogenic emissions. However, further emission reductions are needed to meet global health-based air quality standards.

Classification and sources of extremely severe sandstorms mixed with haze pollution in Beijing

Air quality has significantly improved in China; however, new challenges emerge when dust weather is combined with haze pollution during spring in northern China. On March 15, 2021, an extremely severe sandstorm occurred in Beijing, with hourly maximum PM₁₀ and PM_2.5 concentrations reaching 5267.7 μg m^-3 and 963.9 μg m^-3, respectively. Continuous sandstorm events usually lead to complicated pollution status in spring. Three pollution types were identified disregarding the time sequence throughout March. The secondary formation type was dominant, with high ratios of PM_2.5/PM₁₀ (mean 74%) and PM₁/PM_2.5 (mean 52%). This suggests that secondary transformations are the primary cause of heavy pollution, even during the dry seasons. Sandstorm type resulted in dramatic PM₁₀ levels, with a noticeable decrease in PM_2.5/PM₁₀ levels (27%), although PM_2.5 levels remain high. The transitional pollution type was distinguished by an independent increase in PM₁₀ levels, although PM_2.5 and PM₁ levels differed from the PM₁₀ levels. Throughout March, the sulfur oxidation rate varied considerably, with high levels during most periods (mean 0.52). A strong correlation indicated that relative humidity was the primary variable promoting the formation of secondary sulfate. Sandstorms promote heterogeneous reactions by providing abundant reaction surfaces from mineral particles, therefore aggravating secondary pollution. The sandstorm air mass from the northwest passing through the sand sources of Mongolia carried not only crustal matter but also organic components, such as bioaerosols, resulting in a sharp increase in the organic carbon in PM_2.5.

Impact of sand and dust storms on tropospheric parameter estimation by GPS

The transport of dust from the Middle East and African deserts affects European and Asian countries at certain times of the year, especially in spring. Turkey is one of these countries, and many dust storm events have occurred in the first half of 2022, which have affected especially the southeastern part of Anatolia. Apart from threatening human health, dust and sand particles, which are described as particulate matter, may possibly affect Global Positioning System (GPS) signals. The purpose of this research is to look into the effects of particulate matter less than 10 μm (PM10) on GPS-estimated precipitable water vapor (PWV). Hourly PM10 and PWV data between April 1, 2022, and June 10, 2022, were utilized. Four different extreme dust concentration events and a benchmark period were investigated separately. Hourly data results showed that correlation coefficients vary according to events, wind directions, and the distance between GPS stations and air quality monitoring stations. Also, other meteorological parameters that affect PWV, such as temperature, relative humidity, and pressure, were investigated and found to have no anomalies that could affect PWV. Hourly and daily correlation coefficients in the benchmark period were significantly lower compared to dusty days, which indicates that there is no real correlation between PM10 and PWV concentrations in clear air conditions. Only with the increase of PM10 to extreme levels does the relationship show itself. Therefore, this study suggests that for all GPS applications, such as positioning or PWV estimation, PM10 concentrations should be considered.

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 (PM_2.5) in areas with different distances from dust source regions, PM_2.5 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 PM_2.5-bound crustal and trace elements increased while secondary inorganic ions decreased at both sites. Crustal materials dominated the increased PM_2.5 mass from non-dust period to dust period in both cities. These were further evidenced by PM_2.5 source apportionment results from positive matrix factorization model. During the dust events, dust sources contributed up to 88% of PM_2.5 mass in Wuhai and ∼38% of PM_2.5 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 PM_2.5 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 PM_2.5 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.

Policy-driven variations in oxidation potential and source apportionment of PM2.5 in Wuhan, central China

China has implemented several control measures to mitigate PM_2.5 pollution and improve air quality, such as the Action Plan for the Prevention and Control of Air Pollution (APPCAP). To comprehensively assess the changes in ambient PM_2.5 concentrations and the corresponding health risk with the implementation of APPCAP, this study examined PM_2.5 samples collected in Wuhan in 2012/2013 and 2018 for water-soluble ions, carbonaceous fractions, and elements, respectively. Dithiothreitol (DTT) assay was used to determine the oxidation potential (OP) of PM_2.5. The positive matrix factorization (PMF) model and the multiple linear regression (MLR) model were used to analyze PM_2.5 sources and the contribution of each source to the OP of PM_2.5. The results showed that PM_2.5 concentrations in Wuhan decreased significantly, however, there was little change in the health risk and a significant increase in intrinsic toxicity. DTT_v (the volume-normalized dithiothreitol) showed high correlations (r > 0.5, p < 0.01) with water-soluble organic carbon (WSOC), organic carbon (OC), secondary ions (NO₃^-, SO₄^2-, and NH₄⁺), and elements. Compared to 2012/2013, the contribution of vehicle emissions and secondary aerosol sources to PM_2.5 increased significantly in 2018. Biomass burning sources significantly contribute to DTT_v in the summer and autumn, and secondary aerosol sources significantly contribute to DTT_v in winter. The human health impacts from coal combustion sources remained high, while vehicle emission sources increased. In the context of decreasing PM_2.5 concentrations, the role of vehicle emissions health impacts is increasingly significant due to the large increment in vehicle ownership and high inherent OP. Therefore, targeting vehicle emissions for control is of great importance for human health and needs to be given great attention in future policymaking.