New particle formation (NPF) event at multi rural sites in China Identifying the characteristics of NPF event Comparing NPF event between clean and polluted conditions Quantifying contribution to the cloud condensation nuclei Implication of climate and air quality Long-term continuous measurements of particle number size distributions with mobility diameter sizes ranging from 3 to 800 nm were performed to study new particle formation (NPF) events at Shangdianzi (SDZ), Mt. Tai (TS), and Lin’an (LAN) stations representing the background atmospheric conditions in the North China Plain (NCP), Central East China (CEC), and Yangtze River Delta (YRD) regions, respectively. The mean formation rate of 3-nm particles was 6.3, 3.7, and 5.8 cm−3·s−1, and the mean particle growth rate was 3.6, 6.0, and 6.2 nm·h−1 at SDZ, TS, and LAN, respectively. The NPF event characteristics at the three sites indicate that there may be a stronger source of low volatile vapors and higher condensational sink of pre-existing particles in the YRD region. The formation rate of NPF events at these sites, as well as the condensation sink, is approximately 10 times higher than some results reported at rural/urban sites in western countries. However, the growth rates appear to be 1–2 times higher. Approximately 12%–17% of all NPF events with nucleated particles grow to a climate-relevant size (>50 nm). These kinds of NPF events were normally observed with higher growth rate than the other NPF cases. Generally, the cloud condensation nuclei (CCN) number concentration can be enhanced by approximately a factor of 2–6 on these event days. The mean value of the enhancement factor is lowest at LAN (2–3) and highest at SDZ (~4). NPF events have also been found to have greater impact on CCN production in China at the regional scale than in the other background sites worldwide. 相似文献
Surface O3 production has a highly nonlinear relationship with its precursors. The spatial and temporal heterogeneity of O3-NOx-VOC-sensitivity regimes complicates the control-decision making. In this paper, the indicator method was used to establish the relationship between O3 sensitivity and assessment indicators. Six popular ratios indicating ozone-precursor sensitivity, HCHO/NOy, H2O2/ HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz, were evaluated based on the distribution of NOx- and VOC-sensitive regimes. WRF-Chem was used to study a serious ozone episode in fall over the Pearl River Delta (PRD). It was found that the south-west of the PRD is characterized by a VOCsensitive regime, while its north-east is NOx-sensitive, with a sharp transition area between the two regimes. All indicators produced good representations of the elevated ozone hours in the episode on 6 November 2009, with H2O2/HNO3 being the best indicator. The threshold sensitivity levels for HCHO/NOy, H2O2/HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz were estimated to be 0.41, 0.55, 10.2, 14.0, 19.1, and 0.38, respectively. Threshold intervals for the indicators H2O2/HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz were able to identify more than 95% of VOC- and NOx-sensitive grids. The ozone episode on 16 November 16 2008 was used to independently verify the results, and it was found that only H2O2/HNO3 and H2O2/NOz were able to differentiate the ozone sensitivity regime well. Hence, these two ratios are suggested as the most appropriate indicators for identifying fall ozone sensitivity in the PRD. Since the species used for indicators have seasonal variation, the utility of those indicators for other seasons should be investigated in the future work.
Lab-scale experiments were conducted to investigate the effects of dissolved organic matter (DOM) on the desorption of Cd in freeze–thaw treated Cd-contaminated soils. The results indicated that DOM significantly facilitated the desorption of Cd from freeze–thaw treated soils when comparing with that of non-frozen soils. Effects of DOM on the Cd desorption were highly dependent on the soil type and contamination concentration. The maximum desorption ratios of Cd by DOM generated from straw and sludge were 15.6% and 13.65%, respectively, in brown soils, and the maximum desorption ratios reached 14.7% and 9.3%, respectively, when using black soils through the same treatment. The higher the Cd contamination concentration in soils, the higher the ratio of Cd desorption by DOM. This was because of the integrated effects of the soil properties changed by the freeze–thaw treatment and the species transformation of Cd. The characteristics of DOM, such as its concentration and properties, had shown obvious impacts on the Cd desorption by DOM. The desorption was promoted with the increased DOM concentration and the hydrophilic fraction, and lowered pH and the low-molecular-weight of DOM. 相似文献
Carbon nanotubes possess unique structures and outstanding properties. However, dispersion and manipulation of carbon nanotubes in solvents severely limit their application. A solution is building carbon nanotube-based microcapsules that combine both the properties of carbon nanotubes and capsules. Carbon nanotube-based microcapsules have indeed great potential applications including catalysts, adsorbents, and controlled-release materials. Here, we built carbon nanotube-based microcapsules by electrostatic self-assembly to develop novel composite materials. The construction and morphology of microcapsules were characterized by Raman spectroscopy, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Pre-films composed of poly(sodium 4-styrenesulfonate) and poly(diallyldimethylammoinum chloride) were assembled onto calcium carbonate (CaCO3) microparticles to construct positive solid templates. The carboxylated carbon nanotubes were then successfully assembled on the CaCO3 template using a self-assembly technique. Ethylene diamine tetraacetic acid (EDTA) was used as a powerful chelating agent to remove the CaCO3 cores by chelation between EDTA and calcium, thus completing the construction of carbon nanotube-based hollow microcapsules. The spherical shapes of the microcapsules were well retained, and the carbon nanotubes were anchored evenly in the polyelectrolyte layers. 相似文献