Abstract:Heavy air pollution accompanied by widespread haze clouds occurred in January 2013 over the North China Plain (NCP). To investigate the controlling factors of the haze formation during the study period of 10-15 January 2013, the air quality modeling system RAMS-CMAQ and multiple observation data including routine weather measurements and the air pollution index (API) released by the Ministry of Environment Protection of China were applied to analyze the temporal and spatial variation features of the meteorological factors and key aerosol components. The simulation results show that a high mass burden of PM2.5, which was higher than the 120 μg m^-3 generally distributed in the Beijing-Tianjin-Tangshan region, central and south Hebei Province, and most parts of the Shandong Province. The visibility over these regions broadly ranged from 5 to 8 km. Furthermore, the mass burden of PM2.5 reached 250-300 μg m^-3 over Beijing, Tianjin, Shijiazhuang, Jinan, and their surrounding regions and exceeded 300 μg m^-3 over their urban areas. Thus, the visibility dropped to 3 km and formed severe haze clouds over these cities. Analysis of the meteorological field shows that compared with the multi-year average, the horizontal wind speed and relative humidity at the surface decreased approximately 20% and increased 10%-40%, respectively, over the Beijing-Tianjin-Tangshan region, central and south Hebei Province, and northern Shandong Province during this pollution episode. Coupled with temperature inversion, these stable atmospheric conditions were favorable for pollutant accumulation, and the extinction ability of soluble particles was significantly enhanced due to the high relative humidity. Thus, the abnormal meteorological field was a primary reason for the haze formation in January 2013 over the NCP. Sulfate, nitrate, and ammonium were the main aerosol components responsible for the haze formation in Beijing. The contribution of these three types of inorganic salts to the total extinction exceeded 50%. Additionally, the nitrate provided the first contribution to the surface extinction at more than 25%, which implies that emissions from the transportation sector, in addition related industry sectors, were major anthropogenic sources of this pollution episode in Beijing.

Abstract:A heavy fog-haze episode occurred over the North China Plain during 11-14 January 2013. To investigate the reason for its formation, the Weather Research and Forecasting (WRF)-Chem model was applied to simulate the temporal and spatial distribution features of air pollutants during this fog-haze episode. Compared with observations, the model can reasonably predict temporal and spatial variation of visibility, meteorological conditions such as temperature, relative humidity (RH), wind, and precipitation, and the surface concentration of PM2.5 (particle matter 2.5 mm or less in aerodynamic diameter) in January 2013 over the North China Plain. The model results show that during the study period, high PM2.5 persisted over southern and eastern parts of Hebei Province and the Tianjin and Beijing areas with the highest daily average value ranging from approximately 400－500 μg m^-3. The analysis of historical climate data from 1951 to 2013 indicated a large positive anomaly (20%－40%) of RH and a negative anomaly (－1 m s^-1) of wind speed during the study period. The sounding data also showed the presence of temperature inversion layers over Beijing with a difference of approximately 5 ℃ and high RH maintained at 80%－90% under 1 km. The model results show that during the study period, water vapor was transported with southerly or easterly wind over the near-surface layer and that dust aerosol was transported with northwesterly wind over the upper layer (850 hPa) to the North China Plain. Such meteorological conditions are favorable for the hygroscopic growth and accumulation of aerosols. The balance analysis of nitrate shows that over the Beijing area, a significant increase in chemistry and transport during the nighttime of 10-14 January 2013, contributed to nitrate concentration and the formation of heavy fog-haze.

Abstract:An aerosol-optical module based on Mie scattering theory has been implemented in the Nested Air Quality Prediction Modeling System (NAQPMS), and a new coupler has been developed to deal with the interaction between the mesoscale meteorology model WRF (Weather Research and Forecasting Model) and NAQPMS. The one-way off-line and two-way coupled WRF-NAQPMS models are compared to simulate the severe haze in the Beijing-Tianjin-Hebei area from 27 September to 1 October 2013. The results show that the simulated meteorological elements and PM2.5 concentrations from the two-way coupled model with the aerosol direct radiation effect are more consistent with observations. During the haze period, the boundary layer meteorological elements change significantly because of the aerosol direct radiation effect over the Beijing-Tianjin-Hebei area: Incoming solar radiation is reduced by 25%, the 2-m temperature decreases by 1 ℃, the turbulent kinetic energy is reduced by 25%, the 10-m wind speed decreases by up to 0.2 m/s, and the planetary boundary layer (PBL) height is reduced by 25%. These changes make the atmospheric boundary layer more stable and further exacerbate air pollution over the areas where it is already severe, for example, the PM2.5 concentration increases by up to 30% over Shijiazhuang City. The analysis indicates that there is a positive feedback mechanism between haze and boundary layer meteorology, and the two-way coupled model incorporating this feedback is helpful for accurate simulation and forecasting of haze pollution processes.

Abstract:By using observations of meteorological variables and PM2.5 concentration, together with the meso-scale numerical Weather Research and Forecasting (WRF) model, the weather conditions and boundary layer meteorological features were investigated during haze periods in Beijing in January 2013. The comparison with observations shows that WRF is able to reasonably reproduce the spatial and temporal distributions of the meteorological variables. Analysis of the heaviest haze periods, which occurred during 10-14 January and 27-31 January, shows that meteorological factors and high concentrations of atmospheric particulates are both responsible for the haze pollution. Small or calm wind and steady atmospheric stratification led to a decrease in atmospheric diffusivity and accumulation of pollutants. In addition, the southerly wind carried surrounding pollutants and water vapor to Beijing, which not only increased pollutant concentrations, but also favored aerosol hygroscopic growth, and extinction increase, which consequently led to haze formation and visibility decrease.

Abstract:The most immediate external objective of urban heavy haze pollution incidents was the weather conditions in addition to the internal reason of emission sources. Based on horizonal and vertical particulate matter (PM) data, conventional and encryption automatic meterological station data, and wind profiler data, the analysis of the influence of changes of different scales circulation patterns and boundary layer structure on the formation, accumulation, and dissipation of heavy pollutions of PM2.5 in Beijing during 21-28 February 2013 was presented. The results showed that, under the control of low or high weak pressure, the gathering of the southwest local wind, southeast transport wind, and north mountain wind, with clockwise wind shears in boundary layer, tended to bring on growth spurts of fine PM. Otherwise, the main cause of long time and steady growth of pollutions was the control of uniform pressure and near-surface south transport wind with high-level steady northwest wind. In addition, the key meteorlogical factor was near-surface low wind, high humidity, and maintaining a temperature inversion to promote and sustain the growth of regional haze pollution. A northwest wind in front of high pressure was a direct external power to disperse pollutions.

Abstract:Atmospheric particulate matter (PM) pollution is serious in Baoding, an industrial city in North China. Carbonaceous aerosols are key components of particles of various sizes. Total carbonaceous aerosols (TCA) account for (49±20)%, (45±19)%, and (19±7)% of PM1.1, PM2.1, and PM2.1-9.0, respectively. The spectral distribution and the amount of enrichment in particulate matter concentration show seasonal variations. During autumn and winter, organic carbon (OC) concentrations in fine particulate matter were 44.0±38.3 and 78.5±30.2 μg m^-3 and elemental carbon (EC) concentrations in fine particulate matter were 3.5±1.6 and 8.5±6.8 μg m^-3, respectively. The geometric mean diameter (GMD) of OC and EC in the whole size range was found to be centered in fine particles. The GMD of the coarse mode (≥2.1 μm) was found to be larger in spring and summer and smaller in autumn and winter. However, the GMD of the coarse mode for EC showed the opposite tendency. The average OC/EC ratios in particles with a diameter less than 0.4 μm were 5.2 in spring, 3.5 in summer, 4.1 in autumn, and 5.4 in winter, respectively. The main origin of the particles below 0.4 μm was local vehicular exhaust, while the carbonaceous particles in other size modes mainly came from combustion of coal and burning of biomass.

Abstract:To study the effects of the stratification changes of water vapor on fog and haze, the variation of visibility relative to the liquid water content and relative humidity observed by microwave radiometer during fog and haze events from October 2011 to February 2012 in Beijing was analyzed. The sequence diagram results showed that atmospheric liquid water content is not a suitable reference for forecasting fog and haze, nor is time variation for forecasting its generation or dissipation. However, the various times in the profile diagram of atmospheric liquid water content can indicate the presence of fog and haze because the stratification of liquid water content obviously changes during the generation and dissipation of fog and haze. Further analysis on the various conditions of the fog and haze showed that variations in relative humidity and liquid water content were concentrated mainly below 3 km. Non-precipitation occurred during fog and haze; fog occurred prior to precipitation, and haze dissipated after the precipitation ended. Under the conditions of heavy fog after precipitation, the variation of atmospheric relative humidity was obvious, and the changing of liquid water content occurred between 3-7 km. Precipitation is favorable for the dissipation of fog because it can increase the humidity level near the ground and consume the water vapor in the air. Heavy fog combined with precipitation resulted in a saturated layer with relative humidity close to 100%, whereas heavy haze with no precipitation did not form a saturated layer, and the relative humidity was relatively low.

Abstract:Based on routine surface meteorological data, upper air sounding data, and atmospheric pollutant observation data collected from 2008 to 2012 in Taiyuan, haze characteristics and its formation mechanism were analyzed under the main synoptic situations, typical meteorological elements, and air pollution. The results show that: 1) The frequency of haze occurrence has obvious seasonal and hourly variations with a high probability in the winter half of the year (65.7%) and during the day from 0800 LST to 1300 LST. 2) The frequency of the static wind is high, and southeast winds prevail on haze days. Heavy haze occurs under higher relative humidity conditions. 3) Stable stratification plays a leading role in atmospheric stability on haze days. The mixed layer is approximately 100 m lower on haze days than on no-haze days. The frequency of inversion conditions at 0800 LST is higher than at 2000 LST. Both the average inversion strength and thickness on haze days are higher than on no-haze days. 4) The high pressure weather situation has a significant effect on haze, and the cyclone weather situation is less likely to give rise to haze. 5) The concentrations of PM10, SO₂, and NO₂ decrease by 32.6%, 48.6%, and 21.7%, respectively, on no-haze days compared with haze days. The concentration of particles and SO₂ significantly increase with higher haze levels. 6) The surface solar radiation intensity is weak and sunshine duration is less on haze days.

Abstract:Using MICAPS data, surface meteorological observations, reanalysis of NECP data, and PM2.5 and PM10 concentration data from the Hengshui Environmental Quality Monitoring Station, the continuous smoggy weather that occurred in Hengshui, Hebei Province, in January 2013 was analyzed in terms of the changes in the concentrations of PM10 and PM2.5, the relationship between pollutant concentrations in smoggy weather and ground elements, and the circulation at the middle and lower levels. The results showed the following: 1) Concentrations of PM10 and PM2.5 were low, from 0600 LST to 0700 LST and from 1600 LST to 2100 LST; the PM10 concentration was at a maximum at 1500 LST, and the PM2.5 concentration was the highest at 0200 LST. 2) The relationship between pollutant concentrations in smoggy weather and surface humidity was not a simple positive or negative correlation. 3) The major sources of air pollution are industrial pollution, dust pollution, coal heating in winter, local pollution sources, and regional pollution in Hengshui. 4) During smoggy weather, relative humidity and visibility were negatively correlated, changes in pressure were small, and north to northeasterly winds with a wind speed of less than 2 m/s were most likely to occur. 5) The airflow at 500 hPa on heavy pollution days was primary zonal, while on less polluted days northwest airflow was strong or there was trough or ridge activity at 500 hPa. 6) During smoggy weather, there was likely to be an inversion layer below 850 hPa at 0800 LST, and the surface pressure field was weak, particularly in the Hebei Plain. Finally, the effects and countermeasures for smoggy weather are discussed.

Abstract:The spatiotemporal characteristics of haze days over central and eastern China have been analyzed. The results show that the major haze values are distributed in the Sichuan Basin, the Beijing-Tianjin-Hebei area, the middle and lower reaches of the Yangtze River, and the central regions of Guangdong and Guangxi. The days with the heaviest and lightest amounts of haze occurred in winter and summer, respectively. The values of the haze days in the central and southwestern Beijing-Tianjin-Hebei megacity area, the Sichuan Basin, and the eastern and southern regions of Northeast China exceeded 20 d. In addition, the maximum climate trend coefficient of the Beijing-Tianjin-Hebei area and the Yangtze and Pearl river deltas was 0.8. The annual average haze days showed an obvious upward trend of 3.69 d (10 a)^-1 and a climate trend coefficient of 0.82, which passes 99.9% statistical significance. Moreover, the spatial distributions of aerosol optical depth (AOD) and tropospheric column NO₂ (TroNO₂) were consistent with the annual average haze days over eastern China, and the energy consumption in China showed a stable upward trend during 1960-2010. These results indicate that the increase in air pollution disposal is a main contributing factor in the increase of haze days.

Abstract:During January 2013, Anhui Province experienced frequent and severe haze, which was characterized as widespread and long-lasting with very low visibility. The potential causes of this long-lasting haze are discussed by using the routine daily ground level observational data of three representative stations and high space-resolution sounding data recorded at two stations in January of the most recent five years, together with trajectory-cluster-statistics analysis. The statistics show that low wind speed and high humidity alone cannot explain the low visibility and abundant haze, which reached historical levels in January 2013. The more frequent and deeper ground inversion, and thus, higher stability of stratification occurring at that time can partly explain these situations. Although the back-trajectories of the air mass at the height of 1 km cannot explain the severe haze in Anhui Province, those at the height of 100 m can sufficiently explain these situations. At the height of 100 m, the northeasterly trajectories corresponded to the lowest average visibility at all three stations. In January 2013, the frequency of trajectories corresponding to the lowest visibility group, or together with the second-lowest group, was the highest among the same period of the most recent five years. Therefore, the main reasons of the low visibility and high haze frequency in Anhui Province in January 2013 were more stable stratification and more controlling air masses from northeast.

Abstract:By using conventional observation data and NCEP reanalysis data, a sustained fog and haze event that occurred in Jiangsu Province in early and middle June was analyzed from several perspectives including pollution, circulation background, surface meteorological characteristics, and vapor, thermal, and dynamic conditions. The results showed that the residue of crop-burning, which caused a large aerosol burden, was the main reason for the sustained haze, whereas the heavy fog was formed mainly by radiation and advection inversions. The aerosol particles also provided condensation nuclei for fog formation. High-level cold air did not completely dissolve the underlying relatively stable stratification. Lower wind speed and higher relative humidity of less than 3 m/s and greater than 80%, respectively, were shown to be favorable for the development of the fog and haze. Frequent weak precipitation processes also played an important role in the fog formation and aggravated the haze conditions. The maintenance of near-surface temperature inversion or nearly neutral stratification provided favorable stratification conditions for the persistence of the fog and haze. Moreover, a strong correlation was present between vertical upward movement and haze development. Underlying weak upward motion with specific moisture conditions was conducive to the upward development of the mist. By using backward trajectory simulation, the authors determined that in addition to local suspended particulate matter, the pollutant transport from Anhui Province was an important factor for the sustained fog and haze. In the northern regions, local pollution sources were the main factors.

Abstract:Pearl River Delta (PRD) is a region in China with severe aerosol pollution and is the focus of early research on haze weather. These studies on haze weather include haze references, scientific concepts, long-term trends, fine-particle pollution, horizontal transfer and vertical diffusion ability, aerosol physical, chemical characteristics, and aerosol optical properties. The results of this research have indicated that the pollution by aerosols over the PRD has worsened in recent years. Aerosol clouds occur all year round, with an area of heavy pollution located at the western side of the Pearl River Estuary. The haze weather mainly occurs from October to the following April, resulting in visibility deterioration. Since the beginning of the 1980s, the frequency of haze weather over the PRD has obviously increased and visibility has deteriorated dramatically. Three major fluctuations in visibility deterioration have been accompanied by development of the economy, which has caused dust pollution, sulfate and dust pollution, and dust, sulfate, and automobile exhaust pollution caused by photochemical processes, respectively. No indication has been made that the long-term tendency of fog and light fog days is affected by human activities or economical development, and its fluctuation was governed by the intrinsic inter-annual and inter-decadal variations of climate. The deterioration of visibility over the PRD is strongly associated with fine-particle pollution. Half of the monthly mean PM10 observations exceeded the mean critical value of the national second graded standard (70 μg m^-3), and all of the mean PM2.5 values exceeded the mean critical value of the U.S. national standard (35 μg m^-3). Some mean values of PM2.5 reached nearly twice the standard value, indicating high concentrations of fine particles. The ratio of PM2.5 to PM10 was also very high at approximately 51%－79%. The monthly mean of black carbon concentration was 5.0 μg m^-3－9.1 μg m^-3. Compared with observations data recorded 20 years ago, the ratio of fine particles has obviously increased. The ratios of organic carbon, nitrate, and ammonium have increased, while that of sulfate slightly decreased and that of calcium obviously decreased. The formation of an airflow stagnation area is the main meteorological condition causing this severe haze weather, which is aggravated by weak vertical transport.