China In Autumn Research Articles

Attenuation Law of Train-Induced Vibration Response of Subgrade in Beijing–Harbin Railway

To investigate environmental vibration in the case of railway subgrade in seasonally frozen regions, field experiments were conducted on the Beijing–Harbin railway subgrade of China in autumn and winter. Vibration acceleration and vibration level attenuation law were analysed based on monitoring results. Accordingly, the influence of the subgrade freeze-thaw states, vehicle load, train formation, and running speed on the subgrade surface environmental vibration was analysed. The vibration response of the subgrade decreased with an increase in the distance from the track. The attenuation curve of the vibration acceleration can be fitted using the negative exponential function, and the attenuation curve of the vibration level can be fitted using the linear function. Additionally, the subgrade vibration response during the frozen period was greater than that during the unfrozen period owing to increased strength and rigidity and decreased damping ratio after subgrade freezing, which increased the vibration response. Moreover, the vibration intensity of the subgrade increased with increase in the vehicle load and formation and decreased with an increase in the driving speed within a particular speed range. The findings of this study provide an objective basis for railway subgrade design and disaster assessment in cold regions of China.

Meteorology driving the highest ozone level occurred during mid-spring to early summer in Shanghai, China

More recent studies highlighted the aggravated surface ozone (O3) pollutions occurred in Spring and Autumn in China, but presenting clear distinctions for different cities. In this study, we observed the most elevated mean daily and maximum daily 8-h (MDA8) O3 concentrations occurred from mid-Spring to early Summer (April, May and June, AMJ) at both urban and remote sites in Shanghai compared to other warm months (March, July, August, September, October), based on the long-term measurements from 2010 to 2019. The typical weather pattern of G-SW (High pressure with predominant winds of southwesterly) recognized by T-mode principal component approach (T-PCA), exhibits the strongest solar radiation and highest daily maximum temperature relative to other weathers in AMJ, leading to not only the most elevated O3 concentration, but also the largest O3 increasing variability in daytime. More importantly, under the G-SW weather condition, the MDA8 O3 concentration presents the greatest increasing rate at 3.95 ppbv/yr from 2010 to 2019 in Shanghai downtown compared to other weather patterns, suggesting that more occurrence and faster exacerbation of O3 pollutions could be expected under the G-SW weather condition in the future. To understand and mitigate high O3 occurrences under the weather pattern of G-SW during AMJ, process analysis by a chemical/dynamical model (WRF-Chem, Weather Research and Forecasting (WRF) model coupled with Chemistry) is conducted to elucidate the strong O3 productivity (19 ppbv/h in daytime), that dominates the high O3 occurrence under the G-SW weather condition. Sensitive studies suggest that under the G-SW weather condition, reduction of VOCs emissions is very effective to prevent the high O3 pollution in Shanghai. The model results show that photochemical productivity decreases by 35% in daytime response to 30% reduction of VOCs emissions, leading to 17.6% mitigation of peak O3 concentration in Shanghai downtown. This result provides valuable information for the development of emission control strategy in Shanghai under different weather conditions.

Validation and Calibration of CAMS PM2.5 Forecasts Using In Situ PM2.5 Measurements in China and United States

An accurate forecast of fine particulate matter (PM2.5) concentration in the forthcoming days is crucial since it can be used as an early warning for the prevention of general public from hazardous PM2.5 pollution events. Though the European Copernicus Atmosphere Monitoring Service (CAMS) provides global PM2.5 forecasts up to the next 120 h at a 3 h time interval, the data accuracy of this product had not been well evaluated. By using hourly PM2.5 concentration data that were sampled in China and United States (US) between 2017 and 2018, the data accuracy and bias levels of CAMS PM2.5 concentration forecast over these two countries were examined. Ground-based validation results indicate a relatively low accuracy of raw PM2.5 forecasts given the presence of large and spatially varied modeling biases, especially in northwest China and the western United States. Specifically, the PM2.5 forecasts in China showed a mean correlation value ranging 0.31–0.45 (0.24–0.42 in US) and RMSE of 38–83 (8.30–16.76 in US) μg/m3, as the forecasting time horizons increased from 3 h to 120 h. Additionally, the data accuracy was found to not only decrease with the increase of forecasting time horizons but also exhibit an evident diurnal cycle. This implies the current CAMS forecasting model failed to resolve the local processes that modulate the diurnal variability of PM2.5. Moreover, the data accuracy varied between seasons, as accurate PM2.5 forecasts were more likely to be derived in the autumn in China, whereas these were more likely in spring in the US. To improve the data accuracy of the raw PM2.5 forecasts, a statistical bias correction model was then established using the random forest method to account for large modeling biases. The cross-validation results clearly demonstrated the effectiveness and benefits of the proposed bias correction model, as the diurnal varied and temporally increasing modeling biases were substantially reduced after the calibration. Overall, the calibrated CAMS PM2.5 forecasts could be used as a promising data source to prevent general public from severe PM2.5 pollution events given the improved data accuracy.

Possible role of Southern Hemispheric sea ice in the variability of West China autumn rain

West China Autumn Rain (WCAR), the last rainy season in China associated with the East Asian summer monsoon, is prone to flooding and secondary disasters and has profound impacts on the economic society. Thus, it is of great interest to understand its variability. Through an analysis with gridded rainfall data and reanalysis data, this study reveals that the variability of WCAR is positively correlated to the boreal summer (austral winter) sea ice concentration (SIC) in the Southern Indian and Pacific Ocean basins. Such a relationship is supported by the SIC-related changes in atmospheric circulations and water vapor transport. Corresponding to a high summer SIC, both the Lake Balkhash trough and the Asian low pressure are deepened, the East Asian jet shifts northward, and the water vapor transport to West China is enhanced during the boreal autumn, providing a favorable background for the increase of WCAR, and vice versa. The potential mechanism of how the boreal summer SIC affects the autumn atmospheric situation is further investigated. Results show that the atmospheric circulation in the high latitudes of the Southern Hemisphere possesses a seasonal persistence from the boreal summer to autumn due to the sea ice persistence. Thus, the boreal summer SIC-related anomalies in the upper-tropospheric winds over the Southern Indian and Pacific Ocean basins can persist to the following autumn and subsequently exert substantial influences on the Eurasian atmospheric circulations via two meridional teleconnections. The counterpart in the lower troposphere contributes to the water vapor transport toward West China. Certainly, this candidate mechanism is a preliminary explanation, and other processes may also act in their linkage.

Dynamic Origin of the Interannual Variability of West China Autumn Rainfall

AbstractThe dynamic origin of the interannual variability of West China autumn rainfall (WCAR), a special weather/climate phenomenon over western-central China in September and October, was investigated via observational diagnosis and numerical simulations. Here we found that the interannual variability of WCAR is closely related to the local horizontal trough, which is passively induced by two lower-level anticyclonic (high pressure) anomalies over East Asia. The anticyclonic anomaly over the south is a Gill-type response to the central and eastern Pacific diabatic cooling, while that over the north is part of the mid- to high-latitude barotropic Rossby wave train, which could be induced by either the thermal forcing of the central and eastern Pacific Ocean sea surface temperature (SST) cooling or that of the subtropical northern Atlantic Ocean SST warming. The quasi-barotropic high pressure anomaly over East Asia acts as an “invisible mountain” that steers the low-level anomalous southwesterly into a southeasterly and hinders the water vapor going farther to the north, leading to enhanced WCAR. However, the real mountain ranges in the region (the Qinglin and Ba Mountains) have no essential impact on the formation and interannual variability of WCAR.

Enhanced biomass burning as a source of aerosol ammonium over cities in central China in autumn

Atmospheric ambient gaseous ammonia (NH3), the most abundant alkaline gas, affects public health and climate change through its key role in the formation of secondary aerosols via reactions with acidic gases. Estimation of the contributions of ammonia sources is very challenging in the urban atmosphere. Stable nitrogen isotope ratio (δ15N) measurements have shown that urban aerosol NH4+ and gaseous NH3 are derived from fossil fuel combustion-related (FF) sources, such as coal combustion, NH3 slip, and vehicle exhaust, and volatilization-related sources, such as agriculture and urban water volatilization. Biomass burning (BB) sources, especially residential biofuel, can produce vast quantities of NH3 and other pollutants and may greatly influence air quality and contribute to increased urban NH3 emissions. In the present study, we continually collected PM2.5 samples at three urban sites in Central China during autumn and analyzed the major water-soluble ions and δ15N values of aerosol NH4+. The concentrations of NH4+ increased as the temperature decreased close to winter, whereas the δ15N values did not show this pattern. According to the Bayesian model after isotope fractionation correction, FF sources contributed to 56.4 ± 17.1%, 46.4 ± 18.2%, and 51.8 ± 14.9% of aerosol NH4+ in Nanchang, Wuhan, and Changsha, respectively, throughout autumn. The contributions from BB sources were 34.5 ± 20.4%, 46.4 ± 21.4%, and 40.4 ± 17.4% for Nanchang, Wuhan, and Changsha, respectively. We also found the fraction of aerosol NH4+ from BB increased in all three cities from September to November 2017, which was likely caused by increased heating demands with the decrease in temperature during the season. Furthermore, BB was responsible for a severe haze event (maximum PM2.5 of 205.69 μg/m3) in Nanchang. These findings suggest government controls to improve air quality should include BB sources in addition to FF sources.

COVID – 19 on Lockdown, Social Distancing and Flattening the Curve – A Review

The novel corona outbreak that started in Wuhan China in Autumn 2019, has infected and killed hundreds of thousands of people all over the world. People around the world are scared because a vaccine has not yet been developed to cure this disease. Scientists and health experts around the world are working hard to develop medical countermeasures to control the spread of the COVID 19 outbreak. COVID-19 pandemic created an unprecedented world crisis to our health and changed the way we perceived our world and our everyday lives. To be able to contain the pattern of transmission of this deadly virus, health experts suggests to each one of us to observe the required safety measures such as social distancing and washing our hands with soap and water in a regular basis and observe a proper hygiene. The role of different mass media channels skyrocketing in our lives on different levels. During this time of the pandemic, mass media have been highly recognized as strongest forces in promoting solidarity to people around the world. It has been followed by an increasing volume of research closed to the footsteps of technological transformations intended to map mass media strongest impacts on how we perceived ourselves during this time of the pandemic. Why lockdown and social distancing amid corona virus? When will this outbreak end? What does flattening the curve mean in relation to Corona Virus? This paper discusses the significance of social distancing, lockdown and flattening the curve as countermeasures in order to win the fight against COVID 19. Meanwhile, other interventions and prevention measures such as, lockdown, community quarantine and social distancing are all the necessary interventions and prevention measures that governments all over the world are urging their citizens to do in order to delay and prevent the spread as well as to flatten the curve against COVID-19.

Analysis of a Severe Regional Haze-fog-dust Episode over North China in Autumn by Using Multiple Observation Data

ABSTRACT The mixing of dust and haze is an important factor in the variation of fine particles. In this study, multiple observation data were used to analyze the characteristics and formation of a haze-fog-dust event that occurred in North China between November 23 and November 30 of 2018. This episode can be roughly divided into two stages, haze-fog and dust, with the transition occurring on November 27. Our analysis shows that stable weather conditions and temperature inversions in North China caused the haze-fog event (November 23–26), during which the PM2.5 concentration gradually increased. After November 27, the arrival of cold air accompanied by dust activity rendered meteorological conditions favorable to air quality in the northern part but not the central or southern part of North China. Instead, continuous adverse conditions and the dust backflow, which trapped dust aerosols in the southern part of North China for nearly two days, were responsible for high PM2.5 concentrations in Jinan and Zhengzhou after November 27 (146 and 156 µg m–3 vs. 114 and 144 µg m–3 before November 27, respectively). This study highlights the effect of dust transport on regional environmental pollution during the autumn and the winter.

Long-term trends and spatiotemporal variations of climate comfort in China during 1966-2016

Climate comfort and its variability are of great importance to human comfort, health and well-being, as humans may suffer dire consequences when they are exposed to the environments with heat or cold stress. The climate comfort index represented the integrated effects of meteorological variables on the human thermal sensation. The annual and seasonal climate comfort index values were calculated based on the monthly data of the temperature, relative humidity, and wind speed from 591 stations in China between 1966 and 2016. Using the empirical orthogonal function analysis, the dominant modes of climate comfort index variations were extracted by the first two modes, which accounted for more than 50% of the total variance. The results showed that the annual and seasonal climate comfort index values displayed a latitudinal gradient, and increased towards the south except for the Qinghai-Tibet Plateau. The most frequently perceived thermal sensations were labeled as ?cold?, ?comfortable?, ?cold? and ?extremely cold? conditions from spring to winter, respectively. For annual and seasonal climate comfort index, the consistent increasing trend was detected in most regions of China in the first mode. The sensitive areas were mainly located in the central, eastern and southern China in winter, while in the northern and western China in summer. In the second mode, the fluctuations between upward and downward trends were observed. The sensitive areas were located in the central China in summer, in the southwestern and southern China in autumn, and in the northern China in winter. This study provides the important information for the improvement of human settlement comfort.

Impacts of degrading permafrost on streamflow in the source area of Yellow River on the Qinghai-Tibet Plateau, China

Many observations in and model simulations for northern basins have confirmed an increased streamflow from degrading permafrost, while the streamflow has declined in the source area of the Yellow River (SAYR, above the Tanag hydrological station) on the northeastern Qinghai-Tibet Plateau, West China. How and to what extent does the degrading permafrost change the flow in the SAYR? According to seasonal regimes of hydrological processes, the SAYR is divided into four sub-basins with varied permafrost extents to detect impacts of permafrost degradation on the Yellow River streamflow. Results show that permafrost degradation may have released appreciable meltwater for recharging groundwater. The potential release rate of ground-ice melt-water in the Sub-basin 1 (the headwater area of the Yellow River (HAYR), above the Huangheyan hydrological station) is the highest (5.6 mm per year), contributing to 14.4% of the annual Yellow River streamflow at Huangheyan. Seasonal/intra- and annual shifts of streamflow, a possible signal for the marked alteration of hydrological processes by permafrost degradation, is observed in the HAYR, but the shifts are minor in other sub-basins in the SAYR. Improved hydraulic connectivity is expected to occur during and after certain degrees of permafrost degradation. Direct impacts of permafrost degradation on the annual Yellow River streamflow in the SAYR at Tanag, i.e., from the meltwater of ground-ice, is estimated at 4.9% that of the annual Yellow River discharge at Tanag, yet with a high uncertainty, due to neglecting of the improved hydraulic connections from permafrost degradation and the flow generation conditions for the ground-ice meltwater. Enhanced evapotranspiration, substantial weakening of the Southwest China Autumn Rain, and anthropogenic disturbances may largely account for the declined streamflow in the SAYR.

Impact of Different Types of ENSO Years on Intensity Changes of Landfalling Tropical Cyclones over China

This study examines whether there are significant differences in intensity and destructiveness of landfalling tropical cyclones (TCs) over China in central Pacific warm (CPW), eastern Pacific warm (EPW) and La Niña (LA) years. By analyzing different seasons and locations of TCs making landfall over China, it was found that TCs in LA years generally had a larger power dissipation index (PDI) and may cause more disasters in China, while TCs in EPW years had a larger PDI over South China in autumn. A larger PDI of TCSC (landing location in Southern China) usually occurred in EPW years and a larger PDI of TCEC (landing location in Eastern China) occurred in LA years, compared with CPW years. The TCs in LA years were generally stronger, more frequent, and of longer duration over China, because of the positive relative humidity (RH) anomalies, the significant anomalous cyclone that occupied the South China Sea (SCS), and the easterly wind anomalies providing a beneficial steering flow for TCs making landfall. In EPW years, although TCs were less frequent, they had stronger intensity when making landfall and a longer lifetime over land which was mainly caused by a broad band of anomalous westerlies over the SCS giving rise to a belt of positive relative vorticity anomalies, as well as the slow translation speed of TCs before landfall supplying more energy for TCs to survive over land. Overall, we conclude that greater caution is warranted when TCs occur in LA and EPW years, as they may result in more serious disasters in China.

Atmospheric aerosol pollution across China: a spatiotemporal analysis of satellite-based aerosol optical depth during 2000–2016

ABSTRACTIncreasing attention has been paid to the deterioration of air quality in China during the past decade. This study presents the spatiotemporal variations of aerosol concentration across China during 2000–2016 using aerosol optical depth (AOD) from the atmospheric product of Moderate Resolution Imaging Spectroradiometer. Percentile thresholds are applied to define AOD days with different loadings. Temporally, aerosol concentration has increased since 2000 and reached the highest level in 2011; then it has declined from 2011 to 2016. Seasonally, aerosol concentration is the highest in summer and the lowest in winter. Spatially, North China and Sichuan Basin are featured by high aerosol concentration with increasing trends in North China and decreasing trends in Sichuan Basin. North, Southeast and Southwest China have been through increasing days with low AOD loading; however, Northeast China has experienced increasing days with high AOD loading. It is likely that air quality influenced by aerosols has notably improved over North China in spring and summer, over Southwest and Southeast China in autumn, but has degraded over Northeast China in autumn.

Full annual cycle tracking of a small songbird, the Siberian Rubythroat Calliope calliope, along the East Asian flyway

We used light-level-based geolocation to study the spatio-temporal behaviour of Siberian Rubythroats Calliope calliope breeding in the Amur region of the Russian Far East. Three retrieved devices revealed long-distance migrations, with southwestward movement from Amur through Northeast China in autumn, with the tracked individuals reaching their wintering grounds in southern China and Indochina without major detours and apparently on a route slightly further west than that of the return migration in spring. A single stopover occurred in two of the three birds in both spring and autumn in China. Migration was faster in spring compared to autumn. The birds spent most of their time in seasonal habitats on their temperate breeding sites, and in less seasonal habitats on their tropical wintering grounds. Departure from and arrival at their breeding site coincided with decreasing and increasing vegetation greenness, respectively. This is the first study presenting year-round tracking data for a songbird migrating from mainland Eurasia to Southeast Asia along the East Asian flyway.

Projected changes in seasonal temperature extremes across China from 2017 to 2100 based on statistical downscaling

Abstract Based on observations of daily temperature at 2052 ground stations and outputs of General Circulation Models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5), we study the changes in seasonal temperature extremes and their spatio-temporal patterns across China during the period from 2071 to 2100 relative to the period from 1971 to 2000. The grid-scale extremes estimated from GCM outputs are statistically downscaled to the site scale by transfer functions developed based on the quantiles of grid-scale simulations and on-site observations of the extremes. The assessment of the downscaled seasonal temperature extremes based on Taylor diagram and two-sample Kolmogorv-Smirnov test show that the seasonal maximum/minimum of daily maximum and minimum temperature can be well represented by the downscaled GCM outputs. The seasonal extremes of daily maximum and minimum temperature increase faster in autumn and winter compared to those in spring and summer. The warm nights defined as seasonal fraction of time with daily minimum temperature higher than its 90th percentile centered on a 5-day window are projected to increase substantially in summer. In general, temperature extremes in northern China increase faster than southern China, especially in autumn and winter. The largest increases in seasonal minimum are identified in the most northeastern China in autumn and winter, with magnitudes of >8 °C. In southern China, the increases of seasonal extremes of daily maximum and minimum temperature are generally

Possible influence of Asian polar vertex contraction on rainfall deficits in China in autumn

The mechanisms governing variations in autumn precipitation are complicated and influenced by a number factors. This paper analyses the characteristics of autumn precipitation in China and investigates the influence of Asian polar vertex contraction on rainfall deficits in China and relevant mechanisms. Autumn precipitation decreased significantly from 1961 to 2012 in mid- and southern China, and the area of the Asia polar vortex (AAV) has decreased significantly since 1988. Asian polar vertex contraction is found to be an important factor in these autumn rainfall deficits in China through the following mechanism. Asian polar vertex contraction causes anomalously high geopotential heights in East Asia (from 25°N to 55°N) and low heights north of 65°N in the upper and lower troposphere, weakening meridional gradients in geopotential height. In the upper troposphere, the westerly and northerly winds are strengthened over high latitudes and westerly winds and the subtropical westerly jet are weakened over the East Asian mid-latitudes. In the lower troposphere, westerly winds are strengthened over high latitudes, westerly winds are weakened in East Asia and along the southern periphery of the Tibetan Plateau, and northerly winds in mid- and southern China are clearly strengthened. Hence, autumn rainfall decreases in mid- and southern China.

Characteristics and Source Apportionment of VOCs of a Petrochemical Industrial Park During Autumn in China

An online continuous monitoring system was used to determine the volatile organic carbons (VOCs) in the ambient air of a typical petrochemical industrial park in autumn (Sep., Oct., Nov.) of 2014. The composition, photochemical reactivity, temporal variation, and source of VOCs were analyzed. The results indicated that the mixing ratio of VOCs in autumnal ambient air of the study area was higher than those of other cities and industrial areas. Alkanes were the most abundant group in the VOC mixing ratio, and no significant temporal difference was observed among the three months studied. However, the alkanes, alkenes, and aromatics presented obvious diurnal variation, with single peak and trough values, while the acetylene exhibited "W"-shaped variation, with two minimum and one maximum values. Source apportionment using positive matrix factorization (PMF) indicated that the sources of VOCs in the study area of natural gas transportation and solvents, such as from leakage or volatile oil refinery processing, followed by other traffic sources and asphalt have some contribution. Alkenes and alkanes were the dominant groups of the source apportionment composition, as expressed by the propylene-equivalent (Propy-Equiv) and maximum incremental reactivity (MIR) methods, respectively.

Decadal Shift in West China Autumn Precipitation and its Association With Sea Surface Temperature

AbstractWest China autumn precipitation (WCAP) is the final stage of the rainy season in mainland China and is characterized as the secondary peak in annual cycle of precipitation in West China. This study reveals that WCAP experienced a significant interdecadal shift around the mid‐1980s, with greatly reduced precipitation after this shift. Features related to the decrease in WCAP include the weakening of warm, wet southerlies prevailing from the oceans to inland China, the weakened Eurasian pattern, and the southward displacement of the East Asian jet stream (EAJS). Further analysis indicates that the interdecadal changes in WCAP may be attributed to the interdecadal increasing of sea surface temperature (SST) in the Indo‐Pacific warm pool (SSTIOP), North Pacific (SSTNP), and central equatorial Pacific (SSTCEP) after the 1980s. The warmer SSTIOP contributes to a weaker meridional land‐sea thermal contrast, which inducts an anomalous local meridional circulation and northerly. The warmer SSTNP stimulates a Rossby wave train that leads to weakened West Pacific subtropical high and accompanying cyclonic circulation anomaly, hindering the transport of water vapor inland from the oceans. The increased SSTCEP leads to the southward displacement of the EAJS and its secondary circulation, generating an anomalous descending branch and reduced WCAP. Numerical simulations further support the conclusions derived from the diagnostic analysis that the decadal warming of the SSTIOP, SSTNP, and SSTCEP synergistically contributes to the reduction of WCAP after the 1980s.

A skilful prediction scheme for West China autumn precipitation

West China is one of the country’s largest precipitation centres in autumn. This region’s agriculture and people are highly vulnerable to the variability in the autumn rain. This study documents that the water vapour for West China autumn precipitation (WCAP) is from the Bay of Bengal, the South China Sea and the Western Pacific. A strong convergence of the three water vapour transports (WVTs) and their encounter with the cold air from the northern trough over Lake Barkersh-Lake Baikal result in the intense WCAP. Three predictors in the preceding spring or summer are identified for the interannual variability of WCAP: (1) sea surface temperature in the Indo-Pacific warm pool in summer, (2) soil moisture from the Hexi Corridor to the Hetao Plain in summer and (3) snow cover extent over East Europe and West Siberian in spring. The cold SSTAs contribute to an abnormal regional meridional circulation and intensified WVTs. The wet soil results in greater air humidity and anomalous southerly emerging over East Asia. Reduced snow cover stimulates a Rossby wave train that weakens the cold air, favouring autumn rainfall in West China. The three predictors, which demonstrate the influences of air-sea interaction, land surface processes and the cryosphere on the WCAP, have clear physical significance and are independent with each other. We then develop a new statistical prediction model with these predictors and the multilinear regression analysis method. The predicted and observed WCAP shows high correlation coefficients of 0.63 and 0.51 using cross-validation tests and independent hindcasts, respectively.

Chemical Characteristics and Source Apportionment of PM2.5 and Long-Range Transport from Northeast Asia Continent to Niigata in Eastern Japan

Seasonal intensive sampling was undertaken for two weeks during each of four seasons from May 2015 to February 2017 at Niigata-Maki station in Niigata, eastern Japan. Daily mean concentrations of PM2.5 ranged from 4.2 µg m–3 to 33.4 µg m–3 during the observation period, which were lower than Japanese Environmental Quality Standard for PM2.5 (35 µg m–3). The higher concentrations of SO42−, NH4+ and OC were observed in spring and summer, which may result from photochemical activity and secondary OC production. The major chemical components of PM2.5 at Niigata-Maki site were SO42−, NO3−, NH4+, OCM, EC and crustal elements. Compared with data at other urban sites, a lower concentration of EC and NO3− and higher OC/EC ratio were observed at Niigata-Maki site, which may result from no significant stationary source and low vehicular traffic in the rural site. PM2.5 source apportionment was characterized by positive matrix factorization (PMF) analysis, and the results inferred four major sources: sea salt (10.2%), biomass combustion (18.9%), soil dust (13.2%) and secondary aerosol (44.4%). The potential source contribution function (PSCF) analysis suggested that the major sources of secondary aerosol and sea salts were domestic in southwest Japan and the Sea of Japan, whereas the sources of biomass combustion and soil dust in specific seasons were long range transportation from the Northeast Asian continent (NEA). Comparing with previous studies in western Japan, this study showed a large domestic contribution of southwest Japan for secondary aerosol, while a larger contribution of the NEA was observed in the previous studies. Significant contribution of biomass combustion from northeast China in autumn, and local area in Niigata and southwest Japan in the other seasons was uniquely observed in this study.

Characteristics of fine particulate matter and its sources in an industrialized coastal city, Ningbo, Yangtze River Delta, China

Chemical information is essential in understanding the characteristics of airborne particles, and effectively controlling airborne particulate matter pollution, but it remains unclear in some regions due to the scarcity of measurement data. In the present study, 92 daily PM2.5 (particulate matter with an aerodynamic diameter≤2.5μm) samples as well as historical observation data of air pollutants were collected in urban Ningbo, one of important industrial cities in the coastal area of the Yangtze River Delta, China in autumn and winter (from Nov. 2014 to Feb. 2015). Various chemical species in PM2.5 were determined including water soluble ions, organic and elemental carbon and elements. Positive matrix factorization model, cluster analysis of back trajectories, potential source contribution function (PSCF) model and concentration-weighted trajectory (CWT) model were used for identifying sources, apportioning contributions from each source and tracking potential areas of sources. The results showed the PM2.5 concentration has been reducing; nonetheless, the concentrations of PM2.5 are still much higher than the World Health Organization guideline with high PM2.5 concentrations observed in autumn and winter for the past few years. During the sampling period, the average PM2.5 mass concentration was 77μg/m3 with the major components of OC, NO3−, SO42−, NH4+ and EC, accounting for 24.7, 18.8, 14.5, 11.8 and 6.4% in the total mass concentration, respectively. When the aerosol pollution got worse during the sampling period, the NO3−, SO42− and NH4+ concentrations increased accordingly and NO3− appeared to increase at fastest rate. SO42− transported from industrial areas led to slight difference in spatial distribution of SO42− in Ningbo. More secondary organic carbon was formed and the enrichment factor values of Cu, Ag, Cd, Sn and Pb increased with the degradation of air quality. Ten types of sources were identified for PM2.5 in the autumn and winter of Ningbo, which are metallurgical industry, biomass burning and waste incineration, manufacturing related with Mo, chlor-alkli chemical industry, oil combustion, vehicular emission, secondary source, soil dust, road dust and manufacturing related with Cr, accounting for 9.4, 4.8, 9.4, 7.6, 8.1, 18.7, 27.6, 2, 7.1 and 5.2% of the total sources, respectively. There were five groups of air parcels arriving in Ningbo, of which inland air masses originating from Shandong province were associated with the highest PM2.5 concentrations. Despite the slight differences, it was obvious that the north of Jiangxi, east of Anhui, west of Jiangsu, south of Shandong were identified as major potential sources-areas of SO42−, NO3−, NH4+, Cl−, OC and EC by both PSCF and CWT models.