Variation Of Haze Research Articles

The relationship between December haze pollution in the Sichuan Basin and preceding climate factors

AbstractHaze pollution (HP) is one of the most serious disasters in the Sichuan Basin (SCB), adversely affecting human health, transportation, tourism and agriculture. HP in December is severe and differs from the haze days in January and February in terms of their temporal variations. To improve the understanding of December haze days in the SCB (DHDSCB), this study not only shows the atmospheric circulations and local meteorological circumstances related with the haze variation, but also analyses its relationship with the prior atmospheric apparent heat source over the Tibetan Plateau (TP) and the sea surface temperature (SST). The key circulation system associated with the interannual variation of the DHDSCB is that the SCB is controlled by the positive geopotential height anomalies and anomalous anticyclonic circulations with weak southwestward water vapour transport. Moreover, unfavourable local meteorological circumstances limit the vertical (horizontal) dispersion of pollutants. In addition, the DHDSCB during 1981–2022 is also found to have significant relationships with two preceding climate factors, which are the atmospheric apparent heat source (Q1) over the western TP in preceding November and the SST difference between the western Maritime Continent and western Australia in preceding autumn. The enhancement of Q1 over the western TP in preceding November is closely related to the midlatitude North Atlantic–southern Mediterranean Middle East–Arabian Sea–TP and its downstream region teleconnection pattern. Consequently, the anticyclonic circulation prevails over the SCB, and SCB is with less precipitation and more haze days in December. The western Maritime Continent and western Australia SST pattern in preceding Autumn is correlated with the Bay of Bengal–eastern TP and its downstream–Japan–Bering Sea teleconnection pattern, providing unfavourable moisture condition for the precipitation over the SCB and leading to the onset, development and maintenance of static weather in December. Therefore, the Q1 over the western TP and the SST pattern over the western Maritime Continent and western Australia may be potential indicators for the subseasonal prediction of HP in the SCB in December.

Molecular and Elemental Tracers‐Based Receptor Modeling of PM2.5 in Suburban Hong Kong With Hourly Time‐Scale Air Quality Considerations

AbstractContinuing control efforts in recent decade have notably brought down fine‐particulate‐matter (PM2.5) pollution to compliance with the annual average air quality objective in Hong Kong. However, short‐term (several hours to few days) PM2.5 pollution sporadically occurred in winter and has become a major focus of attention, calling research in characterizing sources and their variations at hourly timescale. This study reports hourly measurements of PM2.5 and its chemical speciation, including molecular and elemental tracers in suburban Hong Kong in 2020 winter. Hourly PM2.5 was 20.3 ± 7.33 μg m−3, dominated by organics and sulfate. We deployed tracer‐based source apportionment using positive matrix factorization, which resolved six secondary and seven primary sources. Sulfate‐rich and nitrate‐rich factors were the leading PM2.5 contributors. Variation in source contributions under different air masses revealed the Pearl River Delta region and coastal areas to the north are main origins. Elevation in secondary sources was the driving factor in causing high PM2.5 polluted hours. During Chinese New Year holiday, firework emissions partially offset the reductions in anthropogenic sources, even leading to an increased PM2.5. Hour‐by‐hour examination of most polluted and firework event hours enhanced understanding on dynamic variations of haze and firework burning evolution. The mass concentration of firework‐derived PM2.5 was notably lower under “prohibition” than “restriction” control scenario (avg. 3.5 vs. 8.4 μg m−3). Our results highlight the effectiveness of tracer‐based source apportionment in revealing hourly PM2.5 source variations and the necessity of regional joint management to lessen the severity of episodic PM2.5 pollution and health risks.

From Transparent to Opaque: A Route towards Multifunctional Parts Injected with a Single Material.

The technological, social and economic development observed in recent decades brought an exponential increase in consumption and inherent new challenges. Recycling is one of the best solutions to minimize the environmental impact of raw materials. However, multi-material components are difficult or even impossible to recycle. The present work focuses on the reduction in the number of different materials used in multifunctional components. In particular, it intends to assess the potential of injecting molding grades of polypropylene (PP) to produce parts with transparency (haze) gradients. Firstly, several polypropylene grades of different types were identified and injected under various thermal processing conditions, i.e., injection temperature and mold temperature, in order to vary the cooling rate, influencing the growth rate of the spherulites and eventually the presence/absence of α and β crystalline zones. The injected parts' optical properties were then characterized, and the most promising PP grades were identified and selected for subsequent work, namely grade DR 7037.01, showing the widest range of haze (from 29.2 to 68.7%). and PP070G2M, presenting the highest haze value (75.3%). Finally, in an attempt to understand the origin of the haze variations observed, the parts injected with the selected PP grades were further characterized through differential scanning calorimetry (DSC) and polarized light microscopy. It was concluded that the main factor causing the observed haze difference was, apart from the size of the spherulites, the presence of internal layers with different birefringence and, therefore, different refractive indices.

Possible Relationship between January “Warm Arctic–Cold Eurasia” and February Haze in North China

Abstract Haze pollution frequently occurs in North China almost every winter month. However, many previous studies pointed out that the interannual–decadal variations of haze in February were inconsistent with that in early winter, which demonstrated an evident subseasonal change in haze pollution. In this study, we found a close relationship between the “warm Arctic–cold Eurasia” (WACE) pattern in January and the weakened February haze pollution in North China according to monthly composites from 1980 to 2019. Associated with the warming signal in sea ice and the cooling signal in Eurasian soil temperatures, the WACE pattern sustained from January to February. The combined signal of sea ice and soil temperature anomalies and its associated anomalous cyclonic circulations over North China provided an environment conducive to the dispersion of pollutants. The relationship between the WACE pattern and the cyclonic circulation anomaly could also be detected from the large-ensemble CMIP6 simulations. Furthermore, the relationship between the January WACE pattern and the reduction of February haze pollution has been prominently enhanced since the late 1990s, which accurately corresponds to the deep Arctic warming that has emerged since the late 1990s. Significance Statement Haze pollution frequently occurs in North China almost every winter month, but with an apparent subseasonal change. Climate anomalies in the mid- to high latitudes could regulate the variations in haze through atmospheric teleconnection. Our study found a relationship between the “warm Arctic–cold Eurasia” (WACE) pattern in January and the weakened February haze pollution in North China. The lingering signal of the WACE was associated to the anomalous cyclonic circulations over North China in February, which was conducive to the dispersion of pollutants. Furthermore, the relationship between the WACE pattern and February haze pollution has been prominently enhancing since the late 1990s, which accurately corresponds to the emergence of the deep Arctic warming accompanied by the strengthened Eurasian cooling. This investigation is of great significance for subseasonal haze prediction.

Seasonal Variations of Chemical Species and Haze in Titan's Upper Atmosphere

Seasonal variation is significant in Titan's atmosphere owing to the large change of solar insolation resulting from Titan's 26.7° axial tilt relative to the plane of Saturn's orbit. Here we present an investigation of hydrocarbon and nitrile species in Titan's upper atmosphere at 400–1200 km, which includes the mesosphere and the lower thermosphere, over more than one-fourth of Titan's year (2006–2014, L S = 318°–60°), using 18 stellar occultation observations obtained by Cassini/Ultraviolet Imaging Spectrograph. Vertical profiles of eight chemical species (CH4, C2H2, C2H4, C2H6, C4H2, C6H6, HCN, HC3N) and haze particles are retrieved from these observations using an instrument forward model, which considers the technical issue of pointing motion. The Markov Chain Monte Carlo algorithm is used to obtain the posterior probability distributions of parameters in the retrieval, which inherently tests the extent to which species profiles can be constrained. The results show that no change of the species profiles is noticeable before the equinox, while the decrease of atmospheric temperature and significant upwelling in the summer hemisphere are found five terrestrial years afterward. Altitude of the detached haze layer decreases toward the vernal equinox and then disappears, and no reappearance is identified within the time range of our data, which is consistent with observations from Cassini/Imaging Science Subsystem. This study provides observational constraints on the seasonal change of Titan's upper atmosphere and suggests further investigations of the atmospheric chemistry and dynamics therein.

Deep Dehazing Network With Latent Ensembling Architecture and Adversarial Learning.

Most existing dehazing algorithms recover haze-free image by solving the hazy imaging model using estimated transmission map and global atmospheric light. However, inaccurate estimation of these variables and the strong assumptions of imaging model result in unrealistic dehazing results. In this paper, we use the adversarial game between a pair of neural networks to accomplish end-to-end photo-realistic dehazing. To avoid uniform contrast enhancement, the generator learns to simultaneously restore haze-free image and capture the non-uniformity of haze. The modules for the two tasks are assembled in sequential and parallel manners to enable information sharing at different levels, and the architecture of the generator implicitly forms an ensemble of dehazing models that allows for feature selection. A multi-scale discriminator competes with the generator by learning to detect dehazing artifacts and the inconsistency between dehazed image and the spatial variation of haze. Unlike existing works that penalize dehazing artifacts via hand-crafted loss, the proposed algorithm uses the identity mapping in the space of clear-scene images to regularize data-driven dehazing. The proposed work also addresses the adaptability of data-driven dehazing to high-level computer vision task. We propose a task-driven training strategy that can optimize the object detection performance on dehazed images without updating the parameters of object detector. Performance of the proposed algorithm is assessed on the RESIDE, I-Haze, and O-Haze benchmarks. The comparison with ten state-of-the-art algorithms shows that the proposed work is the best performer in most competitions.

A teleconnection between sea surface temperature in the central and eastern Pacific and wintertime haze variations in southern China

Haze pollution in recent decades varies largely with both pollutant emissions and meteorological conditions. Using the discrete wavelet transform (DWT) method, we separate these two influences on haze variations in southern China in the time series of haze observations from 1981 to 2011. This helps us to identify the meteorological influence on interannual variation in haze occurrences in southern China and thus observe a teleconnection between the thermal forcing of sea surface temperature (SST) in the central and eastern Pacific and wintertime haze occurrences in southern China (R = − 0.51, p < 0.05). The total haze days in winter is highest among all seasons over southern China and the climotological mean of number of winter haze days is 7.5 days for the region. Compared with the normal winters, the regional mean of the number of haze days in southern China is reduced by ~ 5 days in the winters with above-normal Niño3.4 SST (during El Niño phases), but increased by ~ 4 days in the winters with below-normal Niño3.4 SST (during La Niña phases). In the warm SST winters, the cumulative consequences of strong winds, more precipitation, and a more unstable atmosphere with an “upper colder and lower warmer” vertical pattern leading to more ascendance can all hinder haze formation, whereas in the cold SST winters, opposite meteorological conditions are favorable to haze formation. These meteorological conditions induced by anomalous SST make wintertime haze pollution in southern China vary from year to year to a large extent. This study suggests a strong sensitivity of winter haze occurrences in southern China to the viability of the SST in the central and eastern Pacific.

Temporal and spatial variations of haze and fog and the characteristics of PM2.5 during heavy pollution episodes in China from 2013 to 2018

In recent years, the frequent occurrence of haze and fog events in East and Central China has caused a serious reduction in atmospheric visibility and had a huge impact on human health. Based on the relative humidity, visibility and PM2.5 concentration, the occurrence frequencies of haze as well as the spatial and temporal variations of fog, haze and mist in China from 2013 to 2018 were analyzed. The occurrence frequency of the three weather phenomena increased from 2013 until 2016, and then decreased. Regarding seasonal distribution, haze days are concentrated in winter, while mist often appears in spring and autumn. Clean fog mainly occurs in high-mountain stations and clean areas with high relative humidity, while polluted fog is more common in densely populated cities. In Beijing, the proportion of clean weather increases year by year, PM2.5 in haze weather in Beijing mainly consists of organic carbon, nitrate, sulfate and other secondary aerosols. Most fog events are accompanied by air pollution. The dominant haze is humid haze, which means that its occurrence and aggravation are usually related to aerosol hygroscopic growth.

Re-evaluating the distribution and variation characteristics of haze in China using different distinguishing methods during recent years

Haze is identified via different methods using hourly visibility, relative humidity (RH) and PM2.5 mass concentration observations collected from 2013 to 2018 at 502 stations in China. An inter-comparison of a new haze identification method (MGB) and other currently used methods (M80 and M90) is performed in this research. Compared with other methods, the MGB method has an advantage in the expression of fine particle pollution characteristics, especially in high humidity areas. The mean value of the correlation coefficient of the daily mean PM2.5 and daily haze hour obtained by MGB in China is 0.69 which is higher than the correlation coefficients of the daily mean PM2.5 and haze hour identified by the other two methods. Compared with M80, the haze identified by MGB and M90 is less influenced by daily or monthly variations of RH.Approximately 75% of haze occurs when the RH is exceeds 60% or the PM2.5 mass concentration is below 105 μg/m3 over China, no matter which haze identification method is used. Haze has obvious regional distribution characteristics and is relatively higher in Beijing-Tianjin-Hebei and its surrounding areas, and the middle and lower reaches of the Yangtze River. The 6-year mean annual total haze identified by the MGB method is 1167 h for mainland China. Compared with MGB, M80 underestimates the haze hour by −34%, and M90 produces a smaller positive overestimation by 18%. The annual total haze hour of China and its three major economic regions shows significant decreasing trends regardless of the identification method used. Daily variation of haze is obtained in this research via automatic visibility measurement. The daily cycles of haze hour identified by MGB and M90 are similar, whereas that identified by M80 behaves differently affected by daily variation of RH. Haze hour is high in winter and low in summer.

High time resolution observation of PM2.5 Brown carbon over Xi'an in northwestern China: Seasonal variation and source apportionment

There is growing evidence suggesting the enhancement of brown carbon (BrC) in severe haze episodes. In this study, hourly measurements of BrC in PM2.5 were conducted in Xi'an, a typical city in northwestern China during winter and summer. The absorption coefficient for methanol exacts at 365 nm (babs365, methanol, which is typically used as a proxy of methanol-soluble BrC) in the winter sampling period was over 7 times than that in summer. The mass absorption cross-section for methanol extracts (MAC365, methanol, normalized by babs365, methanol to organic carbon, OC) in winter sampling period was nearly 1.5 times of that in the summer. During the winter haze days, the average babs365,methanol peaked at midnight and the lowest values in the morning, in contrast to high levels in afternoon and low levels at night in non haze days. Unlike the diurnal patterns in winter, summer babs365, methanol diurnal variation presented high midday and low afternoon levels in haze days. However, in non haze days, the pattern showed high morning levels and night low levels. Haze and non haze variations of chemical species levels, babs365, methanol, and MAC365, methanol during winter and summer sampling time showed that the effects of atmospheric aging were complex and could either enhance or reduce light absorption of BrC. Source apportionment based on positive matrix factorization receptor model and multiple linear regressions showed that primary emission was an important contributor to BrC emissions during the winter sampling period, whereas secondary formation played an important role in summer.

Spatial and temporal distribution characteristics of haze days and associated factors in China from 1973 to 2017

In recent years, more haze days have been detected with the intensification of air pollution in China. Haze is a serious environmental problem that is influencing human health. This study focuses on revealing the spatial and temporal distribution characteristics of haze, haze formation factors, and health risks in China since the reform and opening-up. The purpose of this study is to provide a reference for haze governance and develop suggestions for public health. In this study, haze was identified by visibility and meteorological data from 1973 to 2017. Haze days and visibility on haze days were calculated during this period. By using standard deviation ellipse analysis and principal component regression, we calculated the variation of the haze barycenter, standard deviation in the haze area, and contribution rates of the main influencing factors in nine typical regions. Haze seasonal variation and health risk assessment were also analysed in this study. The results show that the changes in haze in China present as five periods: 1973–1979, 1980–1989, 1990–2001, 2002–2010, and 2011–2017. Haze days in the majority of typical cities in central and eastern China show a tendency of growth or fluctuating growth, and the variation intensified after the 1990s. In most areas, there were about 100 haze days, and the visibility on haze days was approximately 7 km until 2017. The main body of the haze area in China is approximately a diamond-shaped pentagon with BEIJING, CHENGDU, NANNING, GUANGZHOU, and SHANGHAI as the apexes. In addition, GANSU and northeast China are also influenced by haze. The haze situation in typical areas has grown since 1973. The haze centres tended to move outwards, especially from 2002-2010, which was a turning point for haze variation. For most regions, pollutant emissions as well as economic and governance factors were the main contributing factors. Haze has obvious seasonal variation in China. Haze in winter is the heaviest, and then haze in autumn, summer and spring becomes relatively mild. The haze health risk increased sharply and expanded from 1973 to 2017. High- and extremely high-risk areas are still concentrated in the diamond region of the haze area and have expanded along or surround main traffic lines and major cities. Through analysis of the contributions of haze factors in various regions of China, this study suggests that the most important means of haze governance comprise four aspects: I) a reduction of exhaust emissions, II) the implementation of green consumption, travel, and behaviour concepts, III) enhanced governance, and IV) urbanization that is as balanced as possible; furthermore, the development of cities such as enclaves should be promoted to avoid health risks to large cities.

Temporal disparity of the atmospheric systems contributing to interannual variation of wintertime haze pollution in the North China Plain

AbstractPrevious studies indicated that the meridional (northerly or southerly) wind anomalies over East China play an important role in modulating interannual variation of the winter haze pollution in the North China Plain (NCP) mainly via changing surface wind speed and humidity. Here, we report that the factors for the formation of the meridional wind anomalies over East China related to interannual variation of winter haze pollution experienced a significant interdecadal change around the mid‐1990s. Before the mid‐1990s, two upstream atmospheric wave trains contribute to generation of the meridional wind anomalies over East China via inducing significant geopotential height anomalies over northeast Asia. The first occurred over mid‐latitude Eurasia and propagated eastward into East Asia, resembling the East Atlantic‐west Russia (EAWR) pattern. The second propagated eastward along the subtropical Asian jet. Furthermore, during this period, the change in the intensity of East Asian trough (EAT) was closely linked with interannual variation of the winter haze variation in the NCP. By contrast, after the mid‐1990s, the atmospheric wave train along the Asian subtropical jet was not observed. Furthermore, the connection between the EAT intensity and the winter time NCP haze variation was weak. The mid‐latitude EAWR‐like pattern and the El Niño‐Southern Oscillation‐related sea surface temperature anomalies in the tropical Pacific were possible factors that explain the meridional wind anomalies over East China. Understanding the change in the atmospheric anomalies contributing to interannual variation of the haze is essential for the prediction of haze in the NCP.

Diurnal haze variations over the North China plain using measurements from Himawari-8/AHI

The diurnal variations of haze properties are essential in understanding the haze pollution formation and its environmental impact. Ground-based measurements can provide this information with high temporal resolution, but the haze measurements are not spatially continuous. The Advanced Himawari Imager (AHI) sensor onboard the next-generation geostationary satellite Himawari-8 can provide haze properties with high spatial and temporal resolution. In this study, the diurnal variations of haze frequency, haze properties [aerosol optical depth (AOD), Angstrom exponent (AE) and fine-particle ratio (RF)] and cloud cover are jointly analyzed over the North China Plain (NCP) for summer and winter seasons during 2015–2017. Both the haze and cloud scheme and the haze properties are well validated. The results reveal that the haze frequency in winter (33.51%) is much higher than that in summer (6.34%), and the diurnal variations of AOD values in winter (0.2–0.9) are stronger than those in summer (0.5–0.9). The diurnal maximum haze frequency values in summer (16:00 p.m.) occur 3 h later than the most severe pollution (13:00 p.m.), with AOD values of 0.7–0.9, AE values of 1.1–1.2 and RF values of 0.5–0.6. In winter, the haze frequency increases from 9:00 to 15:00. However, no typical diurnal variations of AOD, AE and RF are shown. It is also found that haze frequency exhibits opposite diurnal variations compared with those of clouds.

Negative Emotion under Haze: An Investigation Based on the Microblog and Weather Records of Tianjin, China.

Nowadays, many big cities are suffering from heavy air pollution and continuous haze weather. Compared with the threat on physical health, the influence of haze on people’s mental health is much less discussed in the current literature. Emotion is one of the most important indicators of mental health. To understand the negative impact of haze weather on the emotion of the people, we conducted an investigation based on historical weather records and microblog data in Tianjin, China. Specifically, an emotional thesaurus was generated with a microblog corpus collected from sample data. Based on the thesaurus, the public emotion under haze was statistically described. Then, through correlation analysis and comparative study, the relation and seasonal variation of haze and negative emotion of the public were well discussed. According to the study results, there was indeed a correlation between haze and negative emotion of the public, but the strength of this relationship varied under different conditions. The level of air pollution and weather context were both important factors that influence the mental effects of haze, and diverse patterns of negative emotion expression were demonstrated in different seasons of a year. Finally, for the benefit of people’s mental health under haze, recommendations were given for haze control from the side of government.

Evaluation of Antifingerprint Properties of Plastic Surfaces Used in Automotive Components

The antifingerprint properties of a range of surfaces produced with different technologies (in-mould decoration, in-mould labeling, and painted) were objectively evaluated by depositing on them in standard conditions an artificial fingerprint for direct determination of its visibility. The artificial fingerprint behaves similarly to the real human fingerprints. A classification method is then proposed to classify surfaces on the base of antifingerprint properties by measuring the roughness profile (Ra) and calculating the % variation of gloss (GU 20 and 60°), haze, luminance (L), and diffuse reflectance (R) values after fingerprint deposition. This approach provides an objective and quantitative test method to determine visual antifingerprint properties of coated surfaces, instead of the “easy-to-clean” properties commonly evaluated. The data acquired provides a design guideline for fabricating visually fingerprint-free surfaces by controlling roughness, texture, color, and transparency of surfaces, with the aim of optically masking fingerprints.

Inter‐annual variation of the spring haze pollution over the North China Plain: Roles of atmospheric circulation and sea surface temperature

Haze pollution is a serious air quality issue in China. Previous studies over the North China Plain (NCP) mainly focused on analysing the haze during boreal winter. However, the variation in haze during spring and the related factors remain unclear. This study investigates inter‐annual variation of the spring haze, which is represented by the humidity‐corrected dry extinction coefficient (DEC) over the NCP. During high DEC years, pronounced positive DEC anomalies appear over the NCP and its surrounding regions. Correspondingly, a notable anticyclonic anomaly is observed over Northeast Asia, inducing significant southeasterly wind anomalies over the NCP. The anomalous southeasterly winds reduce wind speed and increase relative humidity, which provides favourable meteorological conditions for accumulation and growth of aerosol pollutants. Further analysis shows that the North Atlantic Oscillation (NAO) contributes to the formation of anticyclonic anomalies over Northeast Asia via downstream propagating atmospheric wave trains. Additionally, positive sea surface temperature (SST) anomalies over the subtropical northeastern Atlantic Ocean may also impact the DEC variation. The linear barotropic model experiment further confirms the important role of subtropical northeastern Atlantic SST anomalies in contributing to the anomalous anticyclone over Northeast Asia and southerly wind anomalies over the NCP region, which are triggered via eastwards propagating atmospheric wave trains. This study gives support to the idea that the NAO and the North Atlantic SST may be potential predictors for the frequently observed springtime NCP haze variation.

Factors affecting relative humidity and its relationship with the long-term variation of fog-haze events in the Yangtze River Delta

Relative humidity (RH) is one of the most important parameters in the study of fog-haze. This paper first estimates the contributions of the key quantities (temperature, water vapor, air pollutant) and their combinations to the relative change of RH, and then investigates the relationships of RH with the long-term variation of haze and fog days based on the meteorological data in the Yangtze River Delta over the period 1970–2010. The main conclusions are as follows. (1) Temperature is the foremost factor influencing RH, with the effect of specific humidity and direct contribution of air pollutant being second and third. (2) RH shows a prominent descending trend in the Yangtze River Delta, due to global warming and the ‘analogous heat island effect’ (AHIE). (3) Decreasing RH was responsible for the reduction of fog days. The AHIE can explain the phenomenon in which fog days in metropolises are less than in small cities. (4) Granger causality analysis of inter-annual variation further shows that increasing aerosol loading Ganger-causes the increasing haze days, rather than meteorological parameters such as RH. High RH would enhance hygroscopic growth of particle and then suppress the planet boundary layer height (PBLH) and lead to more haze days, lower PBLH further increases aerosols and RH, this positive feedback mechanism can be established under the condition of aerosol loading being relatively stable and beyond the threshold for haze formation. (5) If aerosol emissions maintain the status quo, climate cooling would result in serious fog-haze events occurring more frequently in Yangtze River Delta. The research provide a scientific basis for understanding the influence of meteorological factors on RH and the connection between the variation of long term fog-haze days and RH under the background of climate change.

Variations of Haze Pollution in China Modulated by Thermal Forcing of the Western Pacific Warm Pool

In addition to the impact of pollutant emissions, haze pollution is connected with meteorology and climate change. Based on the interannual change analyses of meteorological and environmental observation data from 1981 to 2010, we studied the relationship between the winter haze frequency in central-eastern China (CEC) and the interannual variations of sea surface temperature (SST) over Western Pacific Warm Pool (WPWP) and its underlying mechanism to explore the thermal effect of WPWP on haze pollution variation in China. The results show a significant positive correlation coefficient reaching up to 0.61 between the interannual variations of SST in WPWP and haze pollution frequency in the CEC region over 1981–2010, reflecting the WPWP’s thermal forcing exerting an important impact on haze variation in China. The anomalies of thermal forcing of WPWP could induce to the changes of East Asian winter monsoonal winds and the vertical thermal structures in the troposphere over the CEC region. In the winter with anomalously warm SST over the WPWP, the near-surface winds were declined, and vertical thermal structure in the lower troposphere tended to be stable over the CEC-region, which could be conducive to air pollutant accumulation leading to the more frequent haze occurrences especially the heavy haze regions of Yangtze River Delta (YRD) and Pearl River Delta (PRD); In the winter with the anomalously cold WPWP, it is only the reverse of warm WPWP with the stronger East Asian winter monsoonal winds and the unstable thermal structure in the lower troposphere, which could attribute to the less frequent haze pollution over the CEC region. Our study revealed that the thermal forcing of the WPWP could have a modulation on air environment change in China.

Decadal Changes in Seasonal Variation of Atmospheric Haze over the Eastern United States: Connections with Anthropogenic Emissions and Implications for Aerosol Composition

The current seasonal summer maximum in surface fine particulate matter (PM2.5) over the eastern United States has been well established. We find that this seasonality has historically changed substantially, based on long-term quality assured inverse visibility (1/Vis) data over 1946–1998. The median summer/winter 1/Vis ratio increased from about 0.8 over both the southeastern and northeastern United States in the late 1940s to 1.24 over the southeastern United States and to 1.04 over the northeastern United States in the mid-1970s. This ratio exhibits weaker changes in both regions afterward. The observed PM2.5 seasonality after the year 2000 has similar spatial distribution as that in 1/Vis over the mid-1990s, with systematically higher summer/winter ratios which rapidly weaken after the mid-2000s. From 1956 to 1975, stronger increases in 1/Vis occurred in summer than in winter in both regions, associated with increases in sulfur dioxide emissions and reductions in anthropogenic carbonaceous emissions. O...

Haze variation in valley region its affecting factors

The haze has a great harm on the environment and human health. Based on the daily meteorological observation data including visibility, relative humidity, wind speed, temperature, air pollution index and weather record of Baoji region in China, and using least squares method, wavelet and correlation analysis method, the temporal and spatial characteristics of haze were analyzed. While the factors affecting the haze change were discussed. The results showed that the haze mainly occurs in plain areas, and in hilly areas and mountain the haze frequency is relatively small. Overall the annual average haze is decreasing, especially in winter and spring the reduction trend of haze is most obvious, however, in summer haze is increasing. The haze has a 5-year short period and 10-year and 15-year long-term cycles change. Moreover, there was a significant negative correlation between temperature and wind speed with haze, while the relative humidity was significantly positively correlated with haze. These studies provide the basis for atmospheric environmental monitor and management.