Dust Weather Research Articles

17-Year study on the chemical composition of rain, snow and sleet in very dusty air (Krakow, Poland)

The paper presents the results of long-term (1996–2017) studies of the chemical composition of rain, snow and sleet in one of the cities with the highest concentrations of particulate matter in the air in Europe. The study included measurements of 45 chemical constituents of precipitation as well as its pH and EC. Concentrations of PM10, SO2 and meteorological parameters were also analysed. Differences in Cl and Na concentrations were found depending on the type of precipitation (snow or rain). These differences are most probably caused by anthropogenic factors, however, to a small extent (~18–19%), they are associated with the total variability of the concentrations of these chemical constituents. The differences between the concentrations of the remaining constituents of precipitation analysed are of lesser or negligible importance. The main processes affecting the chemical composition of precipitation are the chemical weathering of suspended dust and the formation of mineral acid aerosols. These processes shape the chemical composition of both rain and snow in a similar manner. The differences between the chemical composition of rain and snow are the result of the concentrations of and mutual relations between selected chemical constituents and precipitation pH. An important factor affecting the pH of precipitation is the effectiveness of the chemical weathering of suspended dust, which may make the precipitation more alkaline. It is very likely that pH-buffering will occur, which can prevent the pH of precipitation from decreasing, especially in cold periods. Long-term observations of variability in the concentrations of the chemical constituents indicate a slight, but rather constant decrease in concentrations of most of the chemical constituents analysed, as well as in the concentrations of PM10 and SO2 in the air in Krakow. The directions of these changes reflect, to a certain extent, the complex transformations of industrial, economic and social conditions in Krakow within that period. The typical ranges of variability of the recorded values of concentrations/measurement values of 22 chemical constituents and the physical characteristics of rain, sleet and snow presented in the paper can be used as reference ranges of these parameters, typical for an area with a significant degree of atmospheric dust pollution.

On the characteristics of solar radiative transfer and participating media in Harbin, China

The ultimate solar radiation received by solar systems is the result of being absorbed and scattered by aerosols, and it is mainly influenced by the geometric structure and composition of the aerosol particles, which can be determined by the formation process. Samples of atmospheric aerosol particles were collected in Harbin from February to April 2019. Gravimetric analysis, transmission electron microscopy, and liquid phase ion chromatography were used to analyze the morphology, mixed structure, and water-soluble ion physicochemical properties of particulate samples. The results showed that the average concentration of particulate matter in dust weather was 648.31 μg / m³. The main mixed structure was an external mixed structure, accounting for 58%, and the mass concentration of water-soluble ions accounted for ∼3.6 % of the total suspended particles. In haze weather, the average concentration of particulate matter was 319.90 μg / m³ and the main mixed structure was a core–shell structure, accounting for 60%. The mass concentration of water-soluble ions accounted for ∼11.9 % of the total suspended particles.

Study on the applicability of key parameters from dust emission scheme in WRF/Chem over northwestern China

In order to more accurate quantitative simulation and forecast of sandstorm in northwest China, in this paper, the dust process occurred in northwest China was simulated by using the WRF/Chem model coupling of Shao2004 dust emission parameterization scheme. The influence of key parameter C in Shao2004 scheme is analyzed set at different values on simulated spatial and temporal dust concentration, estimated vertical dust flux and estimated PM10 and PM2.5 concentration of six stations in northwest China. And by comparing the concentration of PM concentration observed at the sites, the results were listed as: Parameter C has an significant influence on the simulation dust scope and maximum center value of dust concentration and vertical dust flux; Different C values can well simulate the variation trend of PM10 and PM2.5 concentration in dust weather, but only when the C value set as 1, this model can more accurately simulate the change of PM10 and PM2.5 concentration in the dust process in northwest China.

Atmospheric contribution to cations cycling in highly weathered catchment, Guadeloupe (Lesser Antilles)

The important fertilizing role of atmospheric dust, and particularly African dust, in tropical rainforests is increasingly recognized but still poorly quantified. To better evaluate dust input into the Caribbean basin, we sampled critical zone compartments of a small forested volcanic catchment in Guadeloupe (soils, parent rock, atmospheric dust, plants, soil solutions, stream and rain waters). The aims of this study are to track sources of cation nutrients (Ca, Mg, K, Sr) developed on highly weathered soil in the rainforest of Guadeloupe, to quantify plant recycling of these nutrients, and to identify constraints on regolith development and its associated nutrient pool.In the Quiock Creek catchment, a large isotopic range of 87Sr/86Sr and εNd values was observed despite the small scale of observation. Sr isotopic composition of the dissolved load varied from 0.7084 in rainfall to 0.7110 in soil solution, whereas it ranges between 0.7068 and 0.7153 for soil samples and between 0.7096 and 0.7102 for plants. The Nd isotopic composition varied between -8.39 in near-surface soil samples to 2.71 in deeper soil. All samples had an intermediate signature between that of the bedrock endmember (87Sr/86Sr=0.7038; εNd=4.8) and the atmospheric endmember (sea salt: 87Sr/86Sr=0.7092 and Saharan dust: 87Sr/86Sr=0.7187, εNd=-11.5).The regolith was built on pyroclastic deposits, but, because of extreme leaching, the regolith has lost its original bedrock signature and inherited an exogenous atmospheric signature. Our results show that only the chemical weathering of the fresh near-surface minerals can provide nutrients to the ecosystem (first 30cm). However, this dust weathering is too low to sustain the tropical forest ecosystem on its own. The cationic mass balance at the catchment scale, as well as the Sr isotopic signature, show that cation and Sr fluxes are of atmospheric origin only and that original bedrock no longer participates in nutrient cycles. The vegetation reflects the 87Sr/86Sr of the dissolved pool of atmospheric Sr.At the soil-plant scale, the cation-nutrient fluxes provided by vegetation (litter fall+leaf excretion) are major compared to input and output fluxes. The annual Ca, K, Sr and Mg fluxes within the vegetation are, respectively, 31, 28, 20 and 3 times greater than the exported fluxes at the outlet of the basin. The residence time of nutrients in the vegetation is 16 years for K and close to 45 years for Sr, Ca and Mg. These results emphasize the highly efficient vegetative turnover that dominates the nutrient cycle in the Quiock Creek catchment.This first characterization of biogeochemical cycles in the Guadeloupean rainforest suggests that the forest community of Quiock Creek is sustained by a small near-surface nutrient pool disconnected from the deep volcanic bedrock. We also demonstrated that, even with efficient nutrient recycling, Saharan dust plays a significant role in maintaining ecosystem productivity in Guadeloupe over long-time scales.

THE AEROSOLS OPTICAL PROPERTIES INVESTIGATION DURING THE DUST POLLUTION

Abstract. At present, the air environment in China is characterized by complex pollution. In this paper, the pollutant sources, transport paths and aerosol optical properties during the dust pollution was conducted to analyse based on ground-based lidar, space-borne sensor and atmospheric transmission model. Firstly, the NMMB/BSC-Dust model, the VIIRS-Suomi NPP date and HYSPLIT were carried out to analyse the dust transport paths and the dust particle size, and then the concentration of particles was analysed. Finally, the optical properties of aerosol particles in the dust weather were studied. During the formation of this weather, there is high dust in the Gobi and Taklamakan deserts. With the influence of wind direction, the dust moves from north to south, and the dust load significantly increased in southern China. Dust at the low altitude is generally transported from the Taklamakan Desert, while dust at the high altitude is generally transported from the Gobi Desert. The hourly average change of PM10 is from 36 μg/m3 to 818 μg/m3, while the hourly average change of PM2.5 is from 15 μg/m3 to 197 μg/m3. The dust was the main cause of the pollution weather. In this study, the formation process of the dust pollution revealed which can be used to provide guidance for government for the prevention work of dust pollution.

Observation study of aerosol spectrum and meteorological conditions under dust weather in Nanjing

In this paper, the characteristic of aerosol spectrum and meteorological conditions of a dust storm was analyzed on May 2011. To compared with different weather background, another 3 day of aerosol properties were discussed. The results showed that the dust storm was originated in southern Mongolia and central Inner Mongolia, influenced Nanjing through Beijing and Shandong from the direction of southeast. The local pollution was serious before the dust intrusion and the ultrafine particles mainly ≤0.08μm. The coarse particles ≥0.5μm mainly occurred during and after the dust intrusion. Compared with other pollution and clean days in the same season, the aerosol concentration affected by dust storm and local pollution was five times higher than that in the clean days in Nanjing. By the influence of local pollution, the diurnal variation of aerosol showed double peaks which located at about 10:00 and around 20:00, respectively. Dust and precipitation had great influence on aerosol diurnal variation. The dry and wet removal process affected the time of the aerosol concentration peaks.

Public willingness to pay for sand and dust weather mitigation: A case study in Beijing, China

China's capital city, Beijing, has been suffering from sand and dust weather with high frequency since 2000. Billions of dollars have been invested into overcoming this hazard, but research with regard to the economic benefit of mitigating this hazard. This paper employed the contingent valuation method research, attempts to investigate the Beijing households' willingness to pay for sand and dust weather mitigation and its determinants. The willingness to pay data were obtained from a double-bounded discrete choice format. Because of 149 respondents (18% of the total samples) refused to pay for the goods, we applied the spike model for processing the data. The annual mean willingness to pay is 404.35 Chinese Yuan. Beijing households are willing to pay a total amount of 2.18 billion Chinese Yuan annually for mitigating sand and dust weather. Furthermore, respondents' income, presence of children, and social norm are significantly correlated with the willingness to pay. This paper suggested enhancing pro-environment education and that government credibility and will be of great importance in promoting public participation in sand and dust weather management.

Ferdinand von Richthofen’s loess research in China

Ferdinand von Richthofen (1833–1905), a great German geographer and geologist, was well known for his loess research in China. Here we reexamine the background of Richthofen’s loess research and review his contributions and limitations according to the existing literature. An important historical background of Richthofen’s loess research was that foreigners have been authorized to travel in the interior of China since the 1860s as a result of the Treaties of Tientsin. Richthofen made seven comprehensive scientific explorations in China in 1868–1872, whereas loess research was just one of his topics. He experienced dust weather on the Loess Plateau, where he had direct and deep impressions of the transport of dust, which should have helped him develop the hypothesis of the Aeolian origin of loess. Apart from the Aeolian hypothesis, his other achievements include the differentiation of the regenerated loess from the original loess, the discovery of the loess near Nanjing, the identification of the desiccated lakes as sources of dust storms, and the identification of “vertical cleavage” as a major property of loess.

Climate prediction of dust weather frequency over northern China based on sea-ice cover and vegetation variability

Seasonal climate predictions of spring (March‒April‒May) dust weather frequency (DWF) over North China (DWFNC) are conducted based on a previous-summer (June–July–August) normalized difference vegetation index in North China (NDVINC), winter (December–January–February) sea-ice cover index over the Barents Sea (SICBS), and winter Antarctic Oscillation index (AAOI). The year-to-year increment approach is applied to improve the prediction skill. Two statistical prediction schemes—statistical models based on year-to-year-increment-form predictors (SM-DY) and anomaly-form predictors (SM-A)—are applied based on NDVINC, SICBS, and AAOI. The results show that the prediction model using the year-to-year increment approach performs much better in predicting DWFNC, with the correlation coefficient between the average DWFNC and the cross-validated results of SM-DY (SM-A) being 0.80 (0.68) during 1983–2016. A hybrid dynamical–statistical prediction model (HM-DY) is constructed based on NDVINC, SICBS, and a spring 850-hPa geopotential height index, derived from the second version of the NCEP Climate Forecast System. Results show that HM-DY has comparable prediction skill with SM-DY. Both SM-DY and HM-DY are extended to hindcast DWF over the 245 stations in the whole of northern China, indicating comparably high skill. The results show that NDVINC and SICBS account for large variances of the dust climate over northern China. In particular, NDVINC and SICBS can enhance 64% of stations in North China in their prediction of dust climate.

Let You See in Sand Dust Weather: A Method Based on Halo-Reduced Dark Channel Prior Dehazing for Sand-Dust Image Enhancement

The images that are captured in sand storms often suffer from low contrast and serious color cast that are caused by sand dust, and these issues will have significant negative effects on the performance of an outdoor computer vision system. To address these problems, a method based on halo-reduced dark channel prior (DCP) dehazing for sand dust image enhancement is proposed in this paper. It includes three components in sequence: color correction in the LAB color space based on gray world theory, dust removal using a halo-reduced DCP dehazing method, and contrast stretching in the LAB color space using a Gamma function improved contrast limited adaptive histogram equalization (CLAHE), in which a guided filter is used to improve the artifacts of the histogram equalization. Experiments on a large number of real sand dust images demonstrate that the proposed method can well remove the overall yellowing tone and dust haze effect and obtain normal visual colors and a detailed clear image.

Aerosol Data Assimilation Using Data from Fengyun-3A and MODIS: Application to a Dust Storm over East Asia in 2011

Aerosol optical depth (AOD) is the most basic parameter that describes the optical properties of atmospheric aerosols, and it can be used to indicate aerosol content. In this study, we assimilated AOD data from the Fengyun-3A (FY-3A) and MODIS meteorological satellite using the Gridpoint Statistical Interpolation three-dimensional variational data assimilation system. Experiments were conducted for a dust storm over East Asia in April 2011. Each 0600 UTC analysis initialized a 24-hWeather Research and Forecasting with Chemistry model forecast. The results generally showed that the assimilation of satellite AOD observational data can significantly improve model aerosol mass prediction skills. The AOD distribution of the analysis field was closer to the observations of the satellite after assimilation of satellite AOD data. In addition, the analysis resulting from the experiment assimilating both FY-3A/MERSI (Medium-resolution Spectral Imager) AOD data and MODIS AOD data had closer agreement with the ground-based values than the individual assimilation of the two datasets for the dust storm over East Asia. These results suggest that the Chinese FY-3A satellite aerosol products can be effectively applied to numerical models and dust weather analysis.

Temporal and Spatial Exposure of Gaseous Pollutants and Its Influence Factors in Shandong Province

According to the monitoring data of SO2, NO2 and PM10 in Shandong Province from 2005 to 2016, and Daniel Tendency Verification was used to analyze the trends and influencing factors of urban air quality. The results show that: (1) The comprehensive pollution index of Shandong Province showed downtrend during 2010 to 2016 which indicated the ambient air quality was improving. The changes in the main atmospheric pollutants are obvious: SO2 and PM10 show a significant downward trend, and NO2 is relatively stable. (2) In recent years, pollutants in Shandong Province have obvious temporal and spatial changes, and the highest concentration of SO2 has appeared in Zibo City. The area with high concentration of NO2 gradually shifted to the central Shandong Province, while the high concentration of PM10 shifted from south to west. The monthly variation of SO2, NO2 and PM10 had the same tendency. The high concentration appeared in November, December and January and the low concentration occurred from June to September. PM10 had a small peak in the non-heating period (March to April) which was influenced by dust weather. (3) Some artificial control measures such as optimization of industrial and energy structure and regulations of atmospheric pollution sources played important roles in improving air quality in Shandong province. Topography, geomorphology, climate and other natural factors were significant external factors which had effects on the spatial and temporal distribution of air pollutants.

Corona onset gradient of the bundle conductor on AC power lines under sand and dust weather condition at 2,200 m altitude

During spring and autumn, sand storms occur frequently in high-altitude areas of Northwest China. The presence of sand particles may affect the corona characteristics of the bundle conductor on AC power lines. A simulation system of sand and dust weather conditions was established to investigate the corona characteristics of 23 types of bundle conductors in Ping'an County (elevation 2200 m). By using tangent method, the corona onset gradient (COG) was obtained for the first time. Finally, the prediction formula for the COG was proposed considering the sub-conductor radius, bundle number, sand and dust concentration, and sand particle size.

Dust, impure calcite, and phytoliths: Modeled alternative sources of chemical weathering solutes in shallow groundwater

In highly reactive, carbonate terrains that constitute more than one-fifth of critical zone landscapes, quantifying bedrock weathering processes may require understanding the realities of carbonate mineral impurity on solubility, biotically-produced minerals as an integral part of leaky biogeochemical cycles, and dust-deposited minerals as important high-surface-area, first-contact solute sources. The potential impact of these processes has not been thoroughly investigated as groundwater solutes are mostly thought to be sourced from chemical reactions with soil and bedrock, although dust is often viewed as an important delivery mechanism of nutrients to other ecosystems, including those in mountain and tropical settings. We present results of computer and hand-calculated (manual) inverse modeling of two years of stream-water chemistry, spanning a dry and a wet year, for a groundwater-fed headwater stream at the Konza Tallgrass Prairie Long-Term Ecological Research Site in northeastern Kansas. Weathering of the limestone and shale bedrock at the site provide a possible source of solutes to the groundwater-fed stream, but our modeling suggests an alternate source considering the pathway of groundwater recharge likely encounters highly reactive phases before encountering bedrock. We used the mineralogy and geochemistry of local dust collected previously, estimates of a possible chemical composition of phytolith containing potassium, and an impure calcite representing measured limestone bedrock chemistry to show that chemical reactions with the current dust flux are adequate to account for the groundwater chemistry. Average annual amounts were about: 1) 380 kg ha−1 yr−1 dust dissolved, 2) 80 kg ha−1 yr−1 bedrock carbonate dissolved, and 3) 320 kg ha−1 yr−1 phytoliths precipitated. Small amounts of cation exchange were also required to balance the models. There were only small differences between the computer and manual inverse models; both methods resulted in up to 4.6 times more mass of dust dissolved than bedrock. We suggest that dust weathering may be a process that occurs widely, considering the ubiquitous dust flux in continental regions. Significance of researchSolutes in groundwater and in streams fed by groundwater are thought to be mostly derived from aquifer bedrock and soil water recharging the aquifer. This paradigm may fail for landscapes that have been subaerially exposed for 10's to 100's of millions of years in terrains where relatively rapid dissolution of minerals dominates, such as carbonate-mineral dominated rocks like limestone. Here we test whether dust, having high surface area and being the first inorganic solid encountered by meteoric precipitation, could provide enough solutes water to reduce the amount of bedrock that dissolves, extending the timeframe of landscape evolution. We found, through inverse modeling with PHREEQC, that dust can provide 4.6 times as much mass to stream water in merokarst than calcite and that the mass of dust dissolved was the same order of magnitude as local dust deposition. These results give permissive evidence that dust is important to understanding groundwater chemistry.

Analysis of Aerosol Optical Depth Variation Characteristics for 10 years in Urumqi Based on MODIS_C006

Based on the MYD04_L2_C006 dataset gained from Moderate resolution imaging spectroradiometer MODIS Level 2 at 10 km resolution of NASA's EOS (Earth Observing System) from 2006 to 2015, the aerosol optical depths (AODs) for 10 years under the condition of mild above atmospheric pollution (including mild) were analyzed for Urumqi City. The results showed that the average AODs in Urumqi were unimodally distribution over the 10 years. From January to April, the AODs gradually increased. During a year, the annual peak of 0.37±0.19 was in April, and the lowest value of 0.22±0.20 was in October. Owing to the frequent occurrence of dust weather conditions in spring, the largest seasonal variation of AOD was in spring, as the air pollution in the entire area was very serious, followed by summer and winter, with the smallest in autumn. In addition, the urban area was the high AOD value area in Urumqi, as its air pollution was more severe than that in the suburbs. The average value of AOD during the 10 years was 0.293. The highest value of AOD was 0.33 in 2006, and the lowest value of 0.24 was in 2008, which declined to 23.3% of that in 2007. The annual change in AOD in Urumqi over the 10 years rose steadily. Compared with previous studies, the lowest and highest values were both higher to different degrees. Despite the deduction trend in 2015, air pollution in Urumqi was serious in the studied decade, and thus control of such needs to be strengthened.

Prenatal exposure to sand and dust storms and children's cognitive function in China: a quasi-experimental study

While there is evidence that sand and dust storms can have adverse health effects, the effects of such storms on children's cognitive function has not been explored. We examined whether prenatal exposure to sand and dust storms affects children's cognitive function and, if so, whether harmful effects of sand and dust storms vary by the trimester of exposure. This study used nationally representative data from the China Family Panel Studies between 2010 and 2014 and data on sand and dust storms from the national Sand and Dust Weather Almanac. We selected four indicators of children's cognitive function: mathematics test scores, word-recognition test scores, the age the child began speaking in whole sentences, and the age the child began counting from one to ten. Since the annual incidence of sand and dust storms is highly variable and is largely unpredictable, we used a region-and-year fixed-effect model to compare the cognitive function of children born in the same region and year but with varying amounts of prenatal exposure to sand and dust storms. We also investigated whether the effect of sand and dust storms varied by the specific month of prenatal exposure. We included 1236 observations for the analysis of mathematics and word-recognition test scores, 2693 observations in the analysis of the age the child began speaking in whole sentences, and 1951 observations for the analysis of the age the child began counting from one to ten. Every 10 additional days of prenatal exposure to sand and dust storms was associated with a 0·20 SD (95% CI 0·06 to 0·35, p=0·009) reduction in word test scores, 0·04 (-0·00 to 0·09, p=0·089) additional months to begin speaking in sentences, and 0·14 (0·03 to 0·25, p=0·021) additional months to begin counting, but was not significantly associated with mathematics test scores (reduction of 0·02 SD, -0·19 to 0·15). 10 additional days of prenatal exposure to sand and dust storms in the seventh gestational month was associated with a 0·18 SD (0·10 to 0·25) reduction in mathematics test scores, a 0·34 SD (0·18 to 0·50) reduction in word test scores, an additional 0·33 months (0·07 to 0·59) to begin speaking in sentences, and an additional 0·20 months (0·04 to 0·35) to begin counting. Our results suggest that protecting pregnant women from the effects of sand and dust storms in the critical periods of fetal brain development could generate benefits for the cognitive function of the next generation. None.

Seasonal statistical analysis of the impact of meteorological factors on fine particle pollution in China in 2013–2017

Based on long-term PM2.5 data observed at high temporal and spatial resolution, the relationships between PM2.5, primary emission, and weather factors in China during four seasons were examined using statistical analysis. The results reveal that primary emission plays a decisive role in the spatial distribution and seasonal variability of PM2.5, except in western China, where PM2.5 is controlled by dust weather. In addition to the accumulation of primary emissions, unfavorable meteorological conditions for the diffusion of air pollution lead to the occurrence of PM2.5 pollution. The significant dynamic factors affecting PM2.5 concentration are surface wind speed, planet boundary layer height, and ventilation coefficient, especially in winter. The ventilation coefficient is inversely correlated with PM2.5. Better ventilation is more favorable for the dilution and outflow of local PM2.5. However, in spring and autumn, ventilation coefficient and PM2.5 are positively correlated over the southern regions with low emission, indicating that ventilation also affects the inflow of PM2.5 from outside the region. Wind shear, 850 hPa divergence, and vertical velocity have insignificant effects on the long-term variations in PM2.5. The significant thermal factor is 850 hPa temperature in winter, except in the Pearl River Delta and Xinjiang regions. In spring, the influence of each thermal factor is weak. In summer, the influences of temperature and humidity are more significant than in spring. In autumn, the influence of humidity is relatively obvious, compared with other thermal factors. The correlation coefficients between multi-factors regressed and observed PM2.5 concentrations pass the 95% confidence test, and are higher than that of single-factor regression over most regions. The observed data from December 2016 to February 2017 were chosen to test the regression equation. The test result reveals that the regression equation is effective for predicting PM2.5 concentrations over regions with high primary emission.

Association between forestry ecological engineering and dust weather in Inner Mongolia: A panel study

Forestry ecological engineering projects in Western China include the Three-North Shelter Forest Project (TNSFP), the Natural Forest Protection Project (NFPP), the Grain for Green Project (GGP) and the Beijing-Tianjin Sandstorm Source Project (BTSSP). Such projects play an important role in the control of dust weather in Western China. In this research, data on the frequency of sandstorms, sand-blowing and dust-floating weather, the area of four forestry ecological engineering projects, wind, rainfall and vegetation coverage from 2000 to 2010 were collected based on the unit of prefecture-level cities in Inner Mongolia. The panel-data model was used to analyze the quantitative association between forestry ecological engineering and dust weather. The results indicate that wind has a strong promotional effect on dust weather, while forestry ecological engineering and rainfall have a containment effect. In addition, the impacts of the four studied forestry ecological engineering projects on dust weather differ. For every increase of 1000 km2 in the Three-North Shelter Forest Project, the annual number of days of sandstorm weather decreased by 4 days. Similarly, for every increase of 1000 km2 in the Beijing-Tianjin Sandstorm Source Project, the sand-blowing weather decreased by 4.4 days annually. In addition, NFPP and GGP have a more obvious inhibitory effect on the dust-floating weather.

Hourly variations of water-soluble ions under different sand and dust weather processes in Lanzhou, China

In this paper we aimed to collect water-soluble anion and cationic through rapid capturing system of atmospheric fine particles in order to analyze the source of water-soluble ions of atmospheric PM2.5 in Lanzhou city, and the characteristics of hourly concentration changes in different sand and dust weather processes. The author also applied Hysplit4.8 to conduct backward trajectory analysis. The results showed that the correlation between water-soluble ions is instrumental to infer the forms of water-soluble ions in Lanzhou, such as (NH4) 2 SO4, NH4NO3, CaSO4, and NH4Cl. Lanzhou has been severely polluted by sand and dust apart from the increasing amount of Ca2+ under different dust sources and transmission paths. Na+ was also elevated in March, resulted from the dust going through the Hexi Corridor from the Taklimakan. Furthermore, in April Cl− also increased due to the dust being derived from Outer Mongolia then passing Qaidam Basin. In addition, Na+ dramatically went up in the process of precipitation.

Analysis of Spatio-temporal Distribution and Variation Characteristics of Aerosol Optical Depth over the Northwest of China by MODIS C6 Product

This work compared the collection 6 MODIS aerosol optical depth products with sun photometer data from AERONET, and evaluated the applicability of C6 merged data in the northwest of China. The spatio-temporal variation characteristics and influencing factors of AOD over northwest of China were analyzed by MODIS/AQUA C6 MYD08-M3 products from 2006 to 2015, and the results showed that Southern Xinjiang and Guanzhong region of Shanxi province had relatively high AOD, whereas the south of Qinghai and Gansu province had low values; Junggar Basin was the incremental area of AOD for the first 5 years and second 5 years, whereas converse result existed in Qaidam Basin and Hetao area. Temporally, the yearly mean AOD ranged from 0.18 to 0.22, and the declined trend occurred in 2011, and the annual decrease rate was about 0.32%; Because of different intensity and frequency of dust weather, the south of Xinjiang showed a significant interannual variation characteristic; East of the northwest displayed an obviously declining trend from 2011 to 2015, and the yearly mean decrease was about 1.1%. The AOD in north of Xinjiang and Qinghai-Tibet remained stable. The seasonal changes of AOD among different areas over the northwest had the same trend, all gradually declined from spring to autumn, and increased in winter.