Using Si depletion in aerosol to identify the sources of crustal dust in two Chinese megacities

Depletion of Si in transported dust has been recognized for many years. It can be used to distinguish between transported and local dust in cities, although it rarely has been. Here we use the variations of the Si/Al ratio in 15 months of continuous PM_2.5 samples at Beijing (northern China) and Chongqing (southwestern China) to reveal the seasonal patterns of their dust sources. For both cities, peaks of concentration for Si and Al in PM_2.5 corresponded with minima of Si/Al, and could often be linked to pulsed air flow from deserts to the northwest. With significant depletion (up to 80%) and homogeneous distribution at urban and rural sites, Si/Al showed a clear seasonal evolution, which decreased from spring to summer, increased from fall to winter, and collapsed during Chinese Spring Festival, indicating the dominance of transported dust, local fugitive dust and firework influence, respectively. The low ratios implied that desert dust is a common source during spring at Chongqing, whereas its presence during cold season at Beijing was also more frequent than expected. Failing to recognize the depletion of Si may lead to an overestimate of desert dust by 15%–65% when using the average abundance of Al in crust (6%–8%), as in previous studies. The difference in Si/Al ratio between local and transported dust implies that >60% of the dust at Beijing came from outside the city during the springs of 2004–2006. This result can help resolve the contradictory findings on this topic that have been presented earlier.     

Soil CO2 fluxes from direct seeding rice fields under two tillage practices in central China

Agricultural practices affect the production and emission of carbon dioxide (CO₂) from paddy soils. It is crucial to understand the effects of tillage and N fertilization on soil CO₂ flux and its influencing factors for a better comprehension of carbon dynamics in subtropical paddy ecosystems. A 2-yr field study was conducted to assess the effects of tillage (conventional tillage [CT] and no-tillage [NT]) and N fertilization (0 and 210 kg N ha^?1) on soil CO₂ fluxes during the 2008 and 2009 rice growing seasons in central China. Treatments were established following a split-plot design of a randomized complete block with tillage practices as the main plot and N fertilizer level as the split-plot treatment. The soil CO₂ fluxes were measured 24 times in 2008 and 17 times in 2009. N fertilization did not affect soil CO₂ emissions while tillage affected soil CO₂ emissions, where NT had similar soil CO₂ emissions to CT in 2008, but in 2009, NT significantly increased soil CO₂ emissions. Cumulative CO₂ emissions were 2079–2245 kg CO₂–C ha^?1 from NT treatments, and 2084–2141 kg CO₂–C ha^?1 from CT treatments in 2008, and were 1257–1401 kg CO₂–C ha^?1 from NT treatments, and 1003–1034 kg CO₂–C ha^?1 from CT treatments in 2009, respectively. Cumulative CO₂ emissions were significantly related to aboveground biomass and soil organic C. Before drainage of paddy fields, soil CO₂ fluxes were significantly related to soil temperature with correlation coefficients (R) of 0.67–0.87 in 2008 and 0.69–0.85 in 2009; moreover, the Q₁₀ values ranged from 1.28 to 1.55 and from 2.10 to 5.21 in 2009, respectively. Our results suggested that NT rice production system appeared to be ineffective in decreasing carbon emission, which suggested that CO₂ emissions from integrated rice-based system should be taken into account to assess effects of tillage.     

Simulating chemistry–aerosol–cloud–radiation–climate feedbacks over the continental U.S. using the online-coupled Weather Research Forecasting Model with chemistry (WRF/Chem)

The chemistry–aerosol–cloud–radiation–climate feedbacks are simulated using WRF/Chem over the continental U.S. in January and July 2001. Aerosols can reduce incoming solar radiation by up to ?9% in January and ?16% in July and 2-m temperatures by up to 0.16 °C in January and 0.37 °C in July over most of the continental U.S. The NO₂ photolysis rates decrease in July by up to ?8% over the central and eastern U.S. where aerosol concentrations are high but increase by up to 7% over the western U.S. in July and up to 13% over the entire domain in January. Planetary boundary layer (PBL) height reduces by up to ?23% in January and ?24% in July. Temperatures and wind speeds in July in big cities such as Atlanta and New York City reduce at/near surface but increase at higher altitudes. The changes in PBL height, temperatures, and wind speed indicate a more stable atmospheric stability of the PBL and further exacerbate air pollution over areas where air pollution is already severe. Aerosols can increase cloud optical depths in big cities in July, and can lead to 500–5000 cm^?3 cloud condensation nuclei (CCN) at a supersaturation of 1% over most land areas and 10–500 cm^?3 CCN over ocean in both months with higher values over most areas in July than in January, particularly in the eastern U.S. The total column cloud droplet number concentrations are up to 4.9 × 10⁶ cm^?2 in January and up to 11.8 × 10⁶ cm^?2 in July, with higher values over regions with high CCN concentrations and sufficient cloud coverage. Aerosols can reduce daily precipitation by up to 1.1 mm day^?1 in January and 19.4 mm day^?1 in July thus the wet removal rates over most of the land areas due to the formation of small CCNs, but they can increase precipitation over regions with the formation of large/giant CCN. These results indicate potential importance of the aerosol feedbacks and an urgent need for their accurate representations in current atmospheric models to reduce uncertainties associated with climate change predictions.     

Emission factors and particulate matter size distribution of polycyclic aromatic hydrocarbons from residential coal combustions in rural Northern China

Coal consumption is one important contributor to energy production, and is regarded as one of the most important sources of air pollutants that have considerable impacts on human health and climate change. Emissions of polycyclic aromatic hydrocarbons (PAHs) from coal combustion were studied in a typical stove. Emission factors (EFs) of 16 EPA priority PAHs from tested coals ranged from 6.25 ± 1.16 mg kg^?1 (anthracite) to 253 ± 170 mg kg^?1 (bituminous), with NAP and PHE dominated in gaseous and particulate phases, respectively. Size distributions of particulate phase PAHs from tested coals showed that they were mostly associated with particulate matter (PM) with size either between 0.7 and 2.1 μm or less than 0.4 μm (PM_0.4). In the latter category, not only were more PAHs present in PM_0.4, but also contained higher fractions of high molecular weight PAHs. Generally, there were more than 89% of total particulate phase PAHs associated with PM_2.5. Gas-particle partitioning of freshly emitted PAHs from residential coal combustions were thought to be mainly controlled by absorption rather than adsorption, which is similar to those from other sources. Besides, the influence of fuel properties and combustion conditions was further investigated by using stepwise regression analysis, which indicated that almost 57 ± 10% of total variations in PAH EFs can be accounted for by moisture and volatile matter content of coal in residential combustion.     

钢渣吸附处理苯酚废水的研究

采用恒温振荡的方法,考察了钢渣粒径、吸附温度、振荡速度、溶液pH值、溶液初始浓度对苯酚去除率的影响。结果表明,在粒径为120~180目、pH=4.0、苯酚溶液浓度在500 mg/L以内、苯酚/钢渣质量比为1∶1 000时吸附效果最好。钢渣对苯酚的吸附能较好地符合Langmuir和Freundlich吸附等温线,线性相关系数分别为0.9971和0.9916,吸附机理为表面吸附。     

巯基化合物在万寿菊镉解毒中的作用

采用水培实验方法研究了万寿菊体内镉积累和解毒与巯基化合物含量的关系。万寿菊植株分别在镉浓度为0、0.1、0.5、2和8 mg/L的营养液中暴露7 d,测定了根、茎、叶中镉、非蛋白巯基(NPT)、半胱氨酸(Cys)、γ-谷氨酰半胱氨酸(γ-EC)、谷胱甘肽(GSH)和植物络合素(PCs)的含量。植物根、茎、叶中镉含量都随着镉暴露浓度的增加而增加。当溶液中镉浓度较低(0.1～2 mg/L)时,茎叶中NPT、PCs、Cys和γ-EC含量随着镉浓度增加而增大;当镉浓度较高(8 mg/L)时,茎叶中PCs含量迅速降低,GSH含量大幅度增高。在根部,这些巯基化合物的含量几乎不受镉处理影响,且含量较低。以上研究结果表明:PCs在万寿菊镉的解毒机制中发挥一定的作用,暴露于高浓度的镉,GSH比PCs起着更为重要的解毒作用。     

固定化包埋亚硝酸菌短程脱氮与同步除磷工艺研究

为实现常温下低碳源城市生活污水的低能耗脱氮除磷,采用固定化技术和厌氧/好氧/缺氧(AOA)工艺耦合与游离组进行了对比实验研究。在温度为25±1℃、pH为8.0±1、DO为1±0.5 mg/L和HRT为9 h的条件下,两组运行结果表明,固定组具有较高的硝化效率和较强的适应能力,亚硝氮的积累率可以稳定维持在70%以上,对NH4+-N、COD和TP的去除率分别为92.2%、87.2%和81.3%,明显优于游离组。     

生物法-人工湿地组合工艺处理小城镇混合污水研究

为适应小城镇污水处理高效、低耗、管理简单的要求,开展了生物法(水解酸化/生物接触氧化)-人工湿地组合工艺(A/BCO-CW)处理小城镇片区混合污水的研究。结果表明,A/BCO系统在停留时间为3～6 h条件下,对悬浮物和有机物有高的去除效率,COD、BOD5和TSS去除率分别达到63.1%、67.7%和66.2%,避免了人工湿地堵塞和提高处理效率,减少了所需湿地面积44%。全年运行结果表明,在0.30～0.59 m/d水力负荷率下,垂直流-表面流-水平潜流人工湿地组合系统对COD、BOD5和TSS平均去除负荷达9.4、5.1和7.2 g/(m2.d)(42%、71.2%和85.2%);COD、BOD5去除速率常数为74.6±12.1 m/y、166±30.5 m/y,这些数值均处于文献中k值范围的高量程内。A/BCO-人工湿地系统对COD、BOD5和TSS具有好的处理效果,出水水质能够稳定达到《地表水环境质量标准》(GB 3838-2002)的IV类水标准,2种处理方法有效组合起来,所开发的低成本、高效率、可持续运行的城镇废水处理组合系统,将会在实际应用尤其是高有机负荷污水处理中发挥良好效用。     

石膏浆液旋流器的分离性能实验研究

通过理论分析及工程经验对石灰石/石膏法烟气脱硫工艺中石膏浆液脱水系统的旋流器进行优化设计,在与工业实际相近的操作条件下,优选出了一根综合性能较好的旋流器。考察了该旋流器的压力、流量与分离效率之间相互关系,与常规石膏浆液旋流器的分级效率进行了比较,确定了最佳操作条件。结果表明,旋流器的进口流量随着进出口压力差的增大而增大,分离效率随着流量增加先上升后下降。在进口硫石膏颗粒平均粒径为24μm,流量为11.8~14.8 m3/h时,分离效率在85%以上,底流出口10μm、15μm以下的颗粒分别占底流出口颗粒总体积的1%、10%左右,起到了很明显的分级浓缩作用,分离性能也优于常规使用的石膏浆液旋流器。