Surface ozone (O3) has become a critical pollutant impeding air quality improvement in many Chinese megacities. Chengdu is a megacity located in Sichuan Basin in southwest China, where O3 pollution occurs frequently in both spring and summer. In order to understand the elevated O3 during spring in Chengdu, we conducted sampling campaign at three sites during O3 pollution episodes in April. Volatile organic compounds (VOCs) compositions at each site were similar, and oxygenated VOCs (OVOCs) concentrations accounted for the highest proportion (35%-45%), followed by alkanes, alkens (including acetylene), halohydrocarbons, and aromatics. The sensitivity of O3 to its precursors was analyzed using an observation based box model. The relative incremental reactivity of OVOCs was larger than other precursors, suggesting that they also played the dominant role in O3 formation. Furthermore, the positive matrix factorization model was used to identify the dominant emission sources and to evaluate their contribution to VOCs in the city. The main sources of VOCs in spring were from combustion (27.75%), industrial manufacturing (24.17%), vehicle exhaust (20.35%), and solvent utilization (18.35%). Discussions on VOCs and NOx reduction schemes suggested that Chengdu was typical in the VOC-limited regime, and VOC emission reduction would help to prevent and control O3. The analysis of emission reduction scenarios based on VOCs sources showed that the emission reduction ratio of VOCs to NO2 needs to reach more than 3 in order to achieve O3 prevention. Emission reduction from vehicular exhaust source and solvent utilization source may be more effective. 相似文献
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In this research, desert sand is used as the sensible heat storage medium, which exchanges heat with air in the downcomer to realize heat storage and heat release. The desert sand distribution uniformity has a significant impact on the heat exchange performance and efficiency between desert sand and air for the process of convection in the downcomer. Given the superiority of sensible heat storage in convective heat transfer between desert sand and air, distributors with cylinder or conical bore solid particles and homogeneity performance testing device are designed and manufactured on the basis of convection system equipped with solid particle–air downcomer. Then, the convection experiment between solid sand and air is researched. The greater the desert sand flow rate and higher the volume density, the larger the variance of regional mass flow rate and the worse the homogeneity performance. For the cylinder bore distributor, the smaller the sand particle size is, the greater affected the sand groups can be. The sand homogeneity performance is preferable with the two particle size ranges: 0.18-0.25 mm and 0.15-0.18 mm. The total sand flow rate decreases, but the uniformity improves with the increase of the air flow velocity, and the best distribution performance is achieved at an air velocity of 0.6 m/s. However, the distribution performance declines with the air flow velocity persistently increasing because the sand groups are pushed to one pipe side close to the wall. The sand groups deflect seriously with the air flow velocity increasing. 相似文献
A work applied response surface methodology coupled with Box–Behnken design (RSM-BBD) has been developed to enhance styrene recovery from waste polystyrene (WPS) through pyrolysis. The relationship between styrene yield and three selected operating parameters (i.e., temperature, heating rate, and carrier gas flow rate) was investigated. A second order polynomial equation was successfully built to describe the process and predict styrene yield under the study conditions. The factors identified as statistically significant to styrene production were: temperature, with a quadratic effect; heating rate, with a linear effect; carrier gas flow rate, with a quadratic effect; interaction between temperature and carrier gas flow rate; and interaction between heating rate and carrier gas flow rate. The optimum conditions for the current system were determined to be at a temperature range of 470–505 °C, a heating rate of 40 °C/min, and a carrier gas flow rate range of 115–140 mL/min. Under such conditions, 64.52% WPS was recovered as styrene, which was 12% more than the highest reported yield for reactors of similar size. It is concluded that RSM-BBD is an effective approach for yield optimization of styrene recovery from WPS pyrolysis. 相似文献
Numerous contaminants in huge amounts are discharged to the environment from various anthropogenic activities. Waterbodies are one of the major receivers of these contaminants. The contaminated water can pose serious threats to humans and animals, by distrubing the ecosystem. In treating the contaminated water, adsorption processes have attained significant maturity due to lower cost, easy operation and environmental friendliness. The adsorption process uses various adsorbent materials and some of emerging adsorbent materials include carbon- and polymer-based magnetic nanocomposites. These hybrid magnetic nanocomposites have attained extensive applications in water treatment technologies due to their magnetic properties as well as combination of unique characteristics of organic and inorganic elements. Carbon- and polymer-related magnetic nanocomposites are more adapted materials for the removal of various kinds of contaminants from waterbodies. These nanocomposites can be produced via different approaches such as filling, pulse-laser irradiation, ball milling, and electro-spinning. This comprehensive review is compiled by reviewing published work of last the latest recent 3 years. The review article extensively focuses on different approaches for producing various carbon- and polymer-based magnetic nanocomposites, their merits and demerits and applications for sustainable water purification. More specifically, use of carbon- and polymer-based magnetic nanocomposites for removal of heavy metal ions and dyes is discussed in detail, critically analyzed and compared with other technologies. In addition, commercial viability in terms of regeneration of adsorbents is also reviewed. Furthermore, the future challenges and prospects in employing magnetic nanocomposites for contaminant removal from various water sources are presented.