In order to design more reasonable and effective acid deposition control policies, the critical load function (CLF) was established and a two-dimensional critical load function figure was drawn based on the steady-state mass balance (SMB) method. The figure could be divided into five different regions: critical load region (non-control region), S deposition control region, N deposition control region, S and N deposition selective control region and S and N deposition simultaneous control region. According to the region into which the deposition point fell, we could choose the corresponding control approach. With further consideration of high base cation deposition (BCdep) in China, a three-dimensional critical load function surface could be drawn by taking BCdep as a variable. As a case study, critical loads of sulfur and nitrogen for the lateritic red earth in Guangzhou were calculated with current deposition data, vegetation data and soil data obtained by field sampling and laboratory analysis. Results showed that the current deposition point fell into the critical load region and a 75% reduction in BCdep caused the deposition point falling into S deposition control region, which indicated the importance of controlling sulfur deposition. While taking the critical load of nutrient nitrogen into account, the current deposition point fell into N deposition control region and with the reduction of BCdep, the deposition point entered S and N deposition simultaneous control region, which meant sulfur and nitrogen deposition should be controlled at the same time.
Abstract Climate change is known to influence interannual variation in grassland aboveground net primary productivity (ANPP), or seasonal biomass, but direct, long-term ground observations are rare. We present a 22-year (1982-2003) measurement series from the Inner Mongolia grassland, China, to examine the effect of climate change on interannual variations in ANPP and monthly aboveground biomass (MAB). ANPP exhibited no increase over 1982-2003 but there was an association with previous-year precipitation. MAB in May increased by 21.8% from 47.8 g m鈭? (averaged for 1982鈥?984) to 58.2 g m鈭? (2001鈥?003), whereas there was no significant variation in June, July and August, and a decrease of 29.7% in September. The MAB increase in May was correlated with increases in precipitation and temperature in the preceding months. These findings suggest that the effects of climate change on grassland production vary throughout the growing season, with warmer and wetter springs resulting in increased biomass early in the growing season, and drier falls causing a decrease in biomass late in the growing season.
The cloud condensation nuclei (CCN) properties of ammonium sulfate particles mixed with organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene (C5H8) were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for organic particle mass concentrations of 0.5 to 10.0 mu g m(-3), NOx concentrations from under 0.4 ppbv up to 38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 degrees C. At 25 degrees C, the observed CCN activation curves were accurately described by a Kohler model having two internally mixed components, namely ammonium sulfate and secondary organic material. The modeled physicochemical parameters of the organic material were equivalent to an effective hygroscopicity parameter kappa(ORG) of 0.10 +/- 0.03, regardless of the C5H8:NOx concentration ratio for the span of > 200:0.4 to 50:38 (ppbv:ppbv). The volatilization curves (i.e., plots of the residual organic volume fraction against temperature) were also similar for the span of investigated C5H8:NOx ratios, suggesting a broad similarity of particle chemical composition. This suggestion was supported by limited variance at 25 degrees C among the particle mass spectra. For example, the signal intensity at m/z 44 (which can result from the fragmentation of oxidized molecules believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across the range of investigated conditions. In contradistinction to the results for 25 degrees C, conditioning up to 100 degrees C in the thermodenuder significantly reduced CCN activity. The altered CCN activity might be explained by chemical reactions (e.g., decomposition or oligomerization) of the secondary organic material at elevated temperatures. The study's results at 25 degrees C, in conjunction with the results of other chamber and field studies for a diverse range of conditions, suggest that a value of 0.10 +/- 0.05 for kappa(ORG) is representative of both anthropogenic and biogenic secondary organic material. This finding supports the use of kappa(ORG) as a simplified yet accurate general parameter to represent the CCN activation of secondary organic material in large-scale atmospheric and climate models.
The coagulation sink and its role in new particle formation are investigated based on data obtained during the PRIDE-PRD2004 campaign at Xinken of Pearl River Delta, China. Analysis of size distributions and mode contributions of the coagulation sink show that the observed higher load of accumulation mode particles impose a significant effect on the coagulation sink and result in higher coagulation sinks at Xinken despite of the lower total particle number compared with other areas. Hence it is concluded that the higher coagulation sink may depress the occurrence frequency of new particle formation events. The strategies targeting at controlling accumulation mode particles may have influences on the frequency of new particle formation events at this area. The factors affecting the coagulation sink are evaluated. The relatively lower ambient relative humidities may weaken the coagulation sink and facilitate the occurrence of new particle formation events during noontime, while the surmise of nucleation and growth involving organic matter may imply an actually higher coagulation sink than expected. These factors have a significant influence on the ultimate fate of the newly formed nuclei and new particle formation. A comparison of event and non-event days indicates that the coagulation sink is not the only decisive factor affecting new particle formation, other factors including the precursor vapors and photochemical activity are none the less important either. Competition of coagulation sink and high source rate leads to the occurrence of new particle formation events at Xinken. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.
Zhang Y, Zhang L, Ma S, Zhao D, Gao W. Context-adaptive pixel based prediction for intra frame encoding, in Proceedings of the IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2010, 14-19 March 2010, Sheraton Dallas Hotel, Dallas, Texas, USA.; 2010:898–901. 访问链接
Chemical tracer methods for determining contributions to primary organic aerosol (POA) are fairly well established, whereas similar techniques for secondary organic aerosol (SOA), inherently complicated by time-dependent atmospheric processes, are only beginning to be studied. Laboratory chamber experiments provide insights into the precursors of SOA, but field data must be used to test the approaches. This study investigates primary and secondary sources of organic carbon (OC) and determines their mass contribution to particulate matter 2.5 microm or less in aerodynamic diameter (PM2.5) in Southeastern Aerosol Research and Characterization (SEARCH) network samples. Filter samples were taken during 20 24-hr periods between May and August 2005 at SEARCH sites in Atlanta, GA (JST); Birmingham, AL (BHM); Centerville, AL (CTR); and Pensacola, FL (PNS) and analyzed for organic tracers by gas chromatography-mass spectrometry. Contribution to primary OC was made using a chemical mass balance method and to secondary OC using a mass fraction method. Aerosol masses were reconstructed from the contributions of POA, SOA, elemental carbon, inorganic ions (sulfate [SO4(2-)], nitrate [NO3-], ammonium [NH4+]), metals, and metal oxides and compared with the measured PM2.5. From the analysis, OC contributions from seven primary sources and four secondary sources were determined. The major primary sources of carbon were from wood combustion, diesel and gasoline exhaust, and meat cooking; major secondary sources were from isoprene and monoterpenes with minor contributions from toluene and beta-caryophyllene SOA. Mass concentrations at the four sites were determined using source-specific organic mass (OM)-to-OC ratios and gave values in the range of 12-42 microg m(-3). Reconstructed masses at three of the sites (JST, CTR, PNS) ranged from 87 to 91% of the measured PM2.5 mass. The reconstructed mass at the BHM site exceeded the measured mass by approximately 25%. The difference between the reconstructed and measured PM2.5 mass for nonindustrial areas is consistent with not including aerosol liquid water or other sources of organic aerosol.