Extreme haze episodes repeatedly shrouded Beijing during the winter of 2012-2013, causing major environmental and health problems. To better understand these extreme events, we performed a model-assisted analysis of the hourly observation data of PM2.5 and its major chemical compositions. The synthetic analysis shows that (1) the severe winter haze was driven by stable synoptic meteorological conditions over northeastern China, and not by an abrupt increase in anthropogenic emissions. (2) Secondary species, including organics, sulfate, nitrate, and ammonium, were the major constituents of PM2.5 during this period. (3) Due to the dimming effect of high loading of aerosol particles, gaseous oxidant concentrations decreased significantly, suggesting a reduced production of secondary aerosols through gas-phase reactions. Surprisingly, the observational data reveals an enhanced production rate of secondary aerosols, suggesting an important contribution from other formation pathways, most likely heterogeneous reactions. These reactions appeared to be more efficient in producing secondary inorganics aerosols than organic aerosols resulting in a strongly elevated fraction of inorganics during heavily polluted periods. (4) Moreover, we found that high aerosol concentration was a regional phenomenon. The accumulation process of aerosol particles occurred successively from cities southeast of Beijing. The apparent sharp increase in PM2.5 concentration of up to several hundred mu g m(-3) per hour recorded in Beijing represented rapid recovery from an interruption to the continuous pollution accumulation over the region, rather than purely local chemical production. This suggests that regional transport of pollutants played an important role during these severe pollution events

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Abstract. Severe winter haze accompanied by high concentrations of fine particulate matter (PM2.5) occurs frequently in the North China Plain and threatens public health. Organic matter (OM) and sulfate are recognized as major components of PM2.5, while atmospheric models often fail to predict their high concentrations during severe winter haze due to incomplete understanding of secondary aerosol formation mechanisms. By using a novel combination of single-particle mass spectrometry and an optimized ion chromatography method, here we show that hydroxymethanesulfonate (HMS), formed by the reaction between formaldehyde (HCHO) and dissolved SO2 in aerosol water, is ubiquitous in Beijing during winter. The HMS concentration and the molar ratio of HMS to sulfate increased with the deterioration of winter haze. High concentrations of precursors (SO2 and HCHO) coupled with low oxidant levels, low temperature, high relative humidity, and moderately acidic pH facilitate the heterogeneous formation of HMS, which could account for up to 15 % of OM in winter haze and lead to up to 36 % overestimates of sulfate when using traditional ion chromatography. Despite the clean air actions having substantially reduced SO2 emissions, the HMS concentration and molar ratio of HMS to sulfate during severe winter haze increased from 2015 to 2016 with the growth in HCHO concentration. Our findings illustrate the significant contribution of heterogeneous HMS chemistry to severe winter haze in Beijing, which helps to improve the prediction of OM and sulfate and suggests that the reduction in HCHO can help to mitigate haze pollution.

Haze episodes occurred in Beijing repeatedly in 2013, resulting in 189 polluted days. These episodes differed in terms of sources, formation processes, and chemical composition and thus required different control policies. Therefore, an overview of the similarities and differences among these episodes is needed. For this purpose, we conducted one-year online observations and developed a program that can simultaneously divide haze episodes and identify their shapes. A total of 73 episodes were identified, and their shapes were linked with synoptic conditions. Pure-haze events dominated in wintertime, whereas mixed haze-dust (PM2.5/PM10 < 60%) and mixed haze-fog (Aerosol Water/PM2.5 ∼ 0.3) events dominated in spring and summer-autumn, respectively. For all types, increase of ratio of PM2.5 in PM10 was typically achieved before PM2.5 reached ∼150 μg/m(3). In all PM2.5 species observed, organic matter (OM) was always the most abundant component (18-60%), but it was rarely the driving factor: its relative contribution usually decreased as the pollution level increased. The only OM-driven episode observed was associated with intensive biomass-burning activities. In comparison, haze evolution generally coincided with increasing sulfur and nitrogen oxidation ratios (SOR and NOR), indicating the enhanced production of secondary inorganic species. Applicability of these conclusions required further tests with simultaneously multisite observations.

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Summary Rapid industrialization and urbanization has been occurring in China since the introduction of the opening‐up policy in 1978. The demands of building and infrastructure construction have increased rapidly, especially in the transportation and housing sectors in China. Large amounts of construction materials have been required in building construction and maintenance of the railway and road systems, especially steel and cement. Continued cement and steel production will require heavy raw material resource consumption and will emit a great deal of carbon dioxide (CO2). This study forecasts future steel and cement demand and related resource consumption and CO2 emissions for building and transportation infrastructure based on a material flow analysis of China. Furthermore, the effect of prolonging the lifetime of building and transportation infrastructure is appraised. The results indicate that building and transportation infrastructure will increase sharply through 2030. Although the demand for new construction will then decrease, steel and cement consumption will remain at a high level through 2050 because these are needed to maintain roads and railways. In addition, prolonging the lifetime of buildings and infrastructure is a useful way to avoid more raw material consumption and to mitigate CO2 emissions. However, its main effect is to decrease the demolition of buildings and reduce material use for the maintenance of roads and railways. Currently not enough countermeasures have been implemented to realize a low carbon–dematerialization society in the building and transportation construction sector. Future comprehensive efforts should include the reuse of waste construction material and a reduction in raw material consumption intensity by applying technical innovations.