Haze Trends Research Articles

Comparison of bacterial community structure in PM2.5 during hazy and non-hazy periods in Guilin, South China.

The online version contains supplementary material available at 10.1007/s10453-022-09777-0.

Thirty years of the Clean Air Act Amendments: Impacts on haze in remote regions of the United States (1990–2018)

The Clean Air Act Amendments of 1990 were aimed at reducing major environmental threats in the United States, such as acid rain, urban air pollution, toxic air emissions, and regional haze. To this end, there have been major reductions in anthropogenic gaseous emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx). SO2 and NOx are also major contributors to particulate haze, which affects visibility in both urban and rural environments. The Interagency Monitoring of Protected Visual Environments (IMPROVE) network has tracked trends in haze in remote regions of the United States since the late 1980s by reconstructing total light extinction (bext) from speciated particulate concentrations. Regional trends in bext were examined using aggregated data from individual sites. Regional, annual mean short-term trends analyses (2002–2018) indicated strong reductions in bext associated with reduced SO2 and NOx emissions, especially in the eastern United States (−4.3% yr−1, p < 0.001) where haze historically was dominated by sulfate particles. Less improvement occurred in the Intermountain West/Southwest (−0.9% yr−1, p = 0.03) and trends were negative but insignificant along the West Coast (−1.5% yr−1, p = 0.19). On average, across the continental remote United States, bext has decreased at a rate of −2.8% yr−1 (p < 0.001) from 2002 through 2018 and -1.8% yr−1 (p < 0.001) from 1992 through 2018. The composition of haze has shifted away from being sulfate-dominated to having higher contributions from carbonaceous and crustal aerosols. This shift points to the success of combined regulatory activities aimed at reducing anthropogenic emissions over the last three decades. As emissions from regulated sources of SO2 and NOx continue to decline, the contributions to haze from unregulated sources, both anthropogenic and natural, such as oil and gas extraction, international sources, biomass burning, and dust, have increased in importance. Reducing haze from these sources would require additional mitigation strategies and resource management plans.

Uncertainty analysis of spatiotemporal characteristics of haze pollution from 1961 to 2017 in China

The definition of haze day is still controversial, and there are different data sources for haze data in China. This study analyzes the uncertainty of haze data in China, which is a prerequisite for studying haze trends. The overall trends defined by different approaches were relatively consistent, but the average values were different. The annual number of haze days defined by visibility and relative humidity was higher than the number defined by manual observation. The correlation coefficient between the two datasets for the whole country was 0.92, and ranged from 0.7 to 0.9 for different regions. The similarity between the trends of haze days by different approaches was greater in the Yangtze River Delta region and the Pearl River Delta region than in the Southwest Region. Limited impact of relative humidity on the trends of haze days was detected in China and different regions. The influence of station screening was also investigated. Station screening had no effect on the annual average number of haze days and the long-term trend. Based on the above analysis, the haze data defined by visibility and relative humidity were chosen to study the spatial and temporal distributions for China. In terms of seasons, haze days were most frequent in winter and least frequent in summer. Except for the Northwest region, the number of haze days increased noticeably after 1980. Our results can further deepen the understanding of the characteristics of haze pollution, and support the study of the causes of haze pollution in China.

Changes in Haze Trends in the Sichuan-Chongqing Region, China, 1980 to 2016

This study analyzed the long-term variations and trends of haze pollution and its relationships with emission and meteorological factors using the haze days (HDs) data derived from surface observation stations in Sichuan-Chongqing (SCC) region during 1980–2016. The results showed that the multi-year mean number of HDs were 68.7 and 4.9 days for the Sichuan-Basin (SCB) and the rest of SCC region, respectively. The seasonally averaged HDs over SCB reached its maximum in winter (34.7 days), followed by autumn (17.0 days) and spring (11.6 days), and with the minimum observed in summer (5.5 days). The inter-annual variations of HDs in 18 main cities revealed that Zigong, Neijiang, and Yibin, which are located in the southern of SCB, have been the most polluted areas over the SCC region in the past decades. A notable increasing trend in annual HDs over the majority of SCC region was found during 1980–1995, then the trend sharply reversed during 1996–2005, while it increased, fluctuating at some cities after 2006. Seasonally, the increased trend in spring and autumn seems to be the strongest during 1980–1995, whereas the decreased trend in spring and winter was stronger than other seasons during 1996–2005. In addition, a remarkable increasing trend was found in winter since 2006. Using correlation analysis between HDs and emission and meteorological factors during different periods, we found that the variability of local precipitation days (PDs), planetary boundary layer height (PBLH), near-surface wind speed (WS), and relatively humidity (RH) play different roles in influencing the haze pollution change during different historical periods. The joint effect of sharp increase of anthropogenic emissions, reduced PDs and WS intensified the haze pollution in SCB during 1980–1995. In contrast, decreased HDs during 1996–2005 are mainly attributable to the reduction of PM2.5 emission and the increase of PDs (especially in winter). In addition, the decrease of PDs is likely to be responsible for the unexpected increase in winter HDs over SCB in the last decade.

Analysis of the Characteristics of the Haze in Recent 3 Decades in Chengdu

It is valuable to study the characteristics of haze change to make good efforts to control air pollution. The haze days in recent 3 decades in Chengdu were counted by 14 hour method, coming to the following results: 1) the number of haze days in Chengdu has decreased and then increased in the recent 3 decades; 2) the number of haze days in autumn and winter accounts for 70% of the year-round number. The spatial distributed characteristic of haze in Chengdu is that it is rare in northwestern Chengdu and common in southwestern Chengdu. Compared with Dujiangyan, the environmental background field of Chengdu, haze trends to become more serious in Shuangliu; 3) according to the comparative analysis on the AQI of 2013 and number of haze days, the methodologically-counted haze days correspond to moderate pollution weather, and this is well reflected in autumn and winter. It is susceptible to the rainfall system in summer; 4) the primary pollutant in Chengdu is PM2.5, followed by PM10. The climatic background is inimical to pollutant diffusion. Besides, the expansion of urban area and the change of people’s lifestyle are significant causes of the increase in the number of pollution days.

Spatial and temporal variation of haze in China from 1961 to 2012

The purpose of this study is to analyze the climatic characteristics and long-term spatial and temporal variations of haze occurrence in China. The impact factors of haze trends are also discussed. Meteorological data from 1961 to 2012 and daily PM10 concentrations from 2003 to 2012 were employed in this study. The results indicate that the annual-average hazy days at all stations have been increasing rapidly from 4 days in 1961 to 18 days in 2012. The maximum number of haze days occur in winter (41.1%) while the minimum occur in summer (10.4%). During 1961-2012, the high occurrence areas of haze shifted from central to south and east regions of China. The Beijing-Tianjin-Hebei (Jing-Jin-Ji) region, Shanxi, Shaanxi, and Henan Province are the high occurrence areas for haze, while the Yangtze River Delta (YRD) and the Pearl River Delta (PRD) have become regions with high haze occurrences in the last 25 years. Temperature and pressure are positively correlated with the number of haze days. However, wind, relative humidity, precipitation, and sunshine duration are negatively correlated with the number of haze days. The key meteorological factors affecting the formation and dissipation of haze vary for high and low altitudes, and are closely related to anthropogenic activities. In recent years, anthropogenic activities have played a more important role in haze occurrences compared with meteorological factors.

The Temporal and Spatial Distribution of Hazy Days in Cities of Jiangsu Province China and an Analysis of Its Causes

Based on the surface meteorological data of Jiangsu Province during 1980–2012, the climatic characteristics and the trends of haze were analyzed. The results indicated that during 1980–2012 haze days increased; in particular, severe and moderate haze days significantly increased. In the northern and coastal cities of Jiangsu Province China, haze days showed a significant increase. Haze often appeared in fall and winter and rarely in summer in the study area. It also occurred more often inland, and less along the coast. Haze occurred more often in June due to straw burning in the harvest time. The haze day increased during the 1990s over southern and southwestern Jiangsu Province; in central and northern Jiangsu, haze day increased after 2000. The continuous, regional, and regional continuous haze days all showed increasing trends. As the urban area expanded each year, industrial emissions, coal consumption, and car ownership increased accordingly, resulting in regional temperature increase and relative humidity decrease, which formed the urban heat island and dry island effects. Hence, haze formation and maintenance conditions became more favorable for more haze days, which led to the increase of haze days, and the significant increases of continuous, regional, and regional continuous haze days.

Haze trends over the capital cities of 31 provinces in China, 1981–2005

This paper presents the patterns and trends of haze over 31 provincial capitals in China between 1980 and 2005. The haze measurements were based on human visual range observations at 31 synoptic meteorological stations operated by the China Meteorological Administration (CMA). The high haze regions were found in largely populated cities such as Chongqing, Beijing, and Shenyang, while the low haze regions were located in the cities with small populations such as Lhasa, Kunming, and Guiyang in southwestern China and Haikou in southern China. The haziness of the 12 cities shows a significantly (95%) decreasing trend, while that of the 13 cities shows a significantly increasing trend over the 25-year study period. The increases are evident in the eastern and southwestern cities in China. It has also been found that there is a decreasing haze trend in winter but an increasing trend in summer for many cities. Nonetheless, the causality for the reduction of aerosol emissions has not been established. This report is the first survey and preliminary analysis done on haze patterns and trends from 1980 to 2005 over the capital cities of 31 provinces in Mainland China.

Revised Algorithm for Estimating Light Extinction from IMPROVE Particle Speciation Data

The Interagency Monitoring of Protected Visual Environments (IMPROVE) particle monitoring network consists of approximately 160 sites at which fine particulate matter (PM2.5) mass and major species concentrations and course particulate matter (PM10) mass concentrations are determined by analysis of 24-hr duration sampling conducted on a 1-day-in-3 schedule. A simple algorithm to estimate light extinction from the measured species concentrations was incorporated in the 1999 Regional Haze Rule as the basis for the haze metric used to track haze trends. A revised algorithm was developed that is more consistent with the recent atmospheric aerosol literature and reduces bias for high and low light extinction extremes. The revised algorithm differs from the original algorithm in having a term for estimating sea salt light scattering from Cl - ion data, using 1.8 instead of 1.4 for the mean ratio of organic mass to measured organic carbon, using site-specific Rayleigh scattering based on site elevation and mean temperature, employing a split component extinction efficiency associated with large and small size mode sulfate, nitrate and organic mass species, and adding a term for nitrogen dioxide (NO2) absorption for sites with NO2 concentration information. Light scattering estimates using the original and the revised algorithms are compared with nephelometer measurements at 21 IMPROVE monitoring sites. The revised algorithm reduces the underprediction of high haze periods and the overprediction of low haze periods compared with the performance of the original algorithm. This is most apparent at the hazier monitoring sites in the eastern United States. For each site, the PM10 composition for days selected as the best 20% and the worst 20% haze condition days are nearly identical regardless of whether the basis of selection was light scattering from the original or revised algorithms, or from nephelometer-measured light scattering.

Haze trends over the United States, 1980–1995

The patterns and trends of haze over the United States for the period of 1980–1995 are presented. Haze measurements are based on human visual range observations at 298 synoptic meteorological stations operated by the United States Weather Service. There was a significant (∼10%) decline in haziness over the 15-yr period. The reductions were evident throughout the eastern United States as well as over the hazy air basins of California. During the same period, in the eastern United States sulfur emissions also declined by about 10%. However, a causality for the reductions has not been established. This report is an update of an earlier survey of haze patterns and trends from 1950 to 1980.

Haze and sulfur emission trends in the eastern United States

The paper presents the regional and seasonal trends of haziness in the Eastern U.S. from 1948 to 1982. Haze or haziness, measured quantitatively at the extinction coefficient, is derived via the Koschmeider relationship from human observer visibility observations made at airport stations of the National Weather Service. The trend analysis shows significant changes in haziness, particularly in the southeastern part of the U.S. The haze trends are compared to the emission trends of sulfur dioxide. These two parameters exhibit similar regional and seasonal trends.