重庆城区PM2.5中金属浓度及其来源

利用环境空气多金属在线监测仪对23种金属元素连续观测1年,分析了重庆城区PM2.5中金属元素浓度变化规律和来源。23种金属年均浓度值为(2.22±0.42)μg/m3,PM2.5样品中金属元素占2%~4%,浓度较稳定且季度特征明显,同时PM2.5中金属主要为K、Fe、Ca、Zn、Mn、Pb。K、Ca、Mn等3种金属既来源于自然源也来源于人为源,Zn、Pb、Cu、As、Cd等5种金属主要来自人为源。利用因子分析得出重庆城区PM2.5中金属元素主要来自土壤风沙扬尘、机动车尾气排放、冶金工业燃烧排放、燃煤燃烧排放。     

重庆市区灰霾天气变化及特征分析

分析了近15年重庆市区灰霾的时间变化特征以及主要大气污染物与能见度的相关性。1997—2012年,灰霾天气占41.2%,发生天数没有明显变化,严重程度有所减缓。灰霾在冬季发生的天数最多,持续时间长,且容易发生重度的持续灰霾。夏季灰霾天数最少,程度最轻。PM10、PM2.5、SO2、NO2浓度随灰霾的加重而增加,其中PM2.5浓度增幅最大,O3浓度随灰霾的加重而降低。灰霾对能见度的影响大于降水天气对其的影响。灰霾天气下能见度受PM2.5的影响较大,非灰霾天气下,能见度主要受O3的影响。     

Ultra-high adsorption of Hg0 using impregnated activated carbon by selenium

Activated carbon was one of the main adsorptions utilized in elemental mercury (Hg⁰) removal from coal combustion flue gas. However, the high cost and low physical adsorption efficiency of activated carbon injection (ACI) limited its application. In this study, an ultra-high efficiency (nearly 100%) catalyst sorbent-Se_x/Activated carbon (Se_x/AC) was synthesized and applied to remove Hg⁰ in the simulated flue gas, which exhibited 120 times outstanding adsorption performance versus the conventional activated carbon. The Se_x/AC reached 17.98 mg/g Hg⁰ adsorption capacity at 160 °C under the pure nitrogen atmosphere. Moreover, it maintained an excellent mercury adsorption tolerance, reaching the efficiency of Hg⁰ removal above 85% at the NO and SO₂ conditions in a bench-scale fixed-bed reactor. Characterized by the multiple methods, including BET, XRD, XPS, kinetic and thermodynamic analysis, and the DFT calculation, we demonstrated that the ultrahigh mercury removal performance originated from the activated Se species in Se_x/AC. Chemical adsorption plays a dominant role in Hg⁰ removal: Selenium anchored on the surface of AC would capture Hg⁰ in the flue gas to form an extremely stable substance-HgSe, avoiding subsequent Hg⁰ released. Additionally, the oxygen-containing functional groups in AC and the higher BET areas promote the conversion of Hg⁰ to HgO. This work provided a novel and highly efficient carbon-based sorbent -Se_x/AC to capture the mercury in coal combustion flue gas.

Selenium-modified porous activated carbon and the interface functional group promotes the synergistic effect of physical adsorption and chemical adsorption to promote the adsorption capacity of Hg⁰.