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101.
An important class of models, frequently used in hydrology for the forecasting of hydrologic variables one or more time periods ahead, or for the generation of synthetic data sequences, is the class of autoregressive(AR) models. As the AR models belong to the family of linear stochastic difference equations, they have both a deterministic and a stochastic component. The stochastic component is often assumed to have a Gaussian distribution. It is well known that hydrologic observations (e.g., stream flows) are heavily affected by noise. To account explicitly for the observation noise, the linear stochastic difference equation is expressed in state variable form and an observation model is introduced. The discrete Kalman filter algorithm can then be used to obtain estimates of the state variable vector. Typically, in hydrologic systems, model parameters, system noise statistics and measurement noise statistics are unknown, and have to be estimated. In this study an adaptive algorithm is discussed which estimates these quantities simultaneously with the state variables. The performance of the algorithm is evaluated by using simulated data. 相似文献
102.
采用过滤分离、超声洗脱和气质联用等技术,实验测定了柴油机尾气中碳烟颗粒物的质量含量、可溶性有机组分在颗粒物中的质量分数和可溶性有机组分的化学组成。在实验条件下,柴油机尾气中碳烟颗粒物的质量含量为32·6~143·6mg/m3。可溶性有机组分在颗粒物中的质量分数为18·5%~89·4%。可溶性有机组分中检测出有机物100多种,已确定化学结构的有机物73种,其中直链和支链烷烃含量占81·22%,芳烃类化合物17·94%。 相似文献
103.
Many metropolitan transit authorities are considering upgrading transit bus fleets to decrease ambient criteria pollutant
levels. Advancements in engine and fuel technology have lead to a generation of lower-emission buses in a variety of fuel
types. Dynamometer tests show substantial reductions in particulate mass emissions for younger buses (<10 years) over older
models, but particle number reduction has not been verified in the research. Recent studies suggest that particle number is
a more important factor than particle mass in determining health effects. In-vehicle particle number concentration measurements
on conventional diesel, oxidation-catalyst diesel and compressed natural gas transit buses are compared to estimate relative
in-vehicle particulate exposures. Two primary consistencies are observed from the data: the CNG buses have average particle
count concentrations near the average concentrations for the oxidation-catalyst diesel buses, and the conventional diesel
buses have average particle count concentrations approximately three to four times greater than the CNG buses. Particle number
concentrations are also noticeably affected by bus idling behavior and ventilation options, such as, window position and air
conditioning. 相似文献
104.
The particulate organic matter distribution and its elemental composition in the northern and central Adriatic Sea during different seasonal periods are shown, highlighting the principal processes and factors influencing their distribution and characteristics.
In the low salinity waters the concentrations of particulate carbon, nitrogen and phosphorus were higher and more variable than in the dense waters, mainly due to dilution effects which induce an abundant phytoplankton growth.
Generally in summer the particulate organic matter distribution followed the trophic gradient while in winter resuspension events often became more important. Differences between summer and winter were more evident in the diluted waters and were mainly due to the seasonal heat exchanges and to the fresh water inputs.
Marked differences in C/P ratios were observed in the POM: high ratios in the northern diluted waters and low in the more saline waters and in the central Adriatic. 相似文献
In the low salinity waters the concentrations of particulate carbon, nitrogen and phosphorus were higher and more variable than in the dense waters, mainly due to dilution effects which induce an abundant phytoplankton growth.
Generally in summer the particulate organic matter distribution followed the trophic gradient while in winter resuspension events often became more important. Differences between summer and winter were more evident in the diluted waters and were mainly due to the seasonal heat exchanges and to the fresh water inputs.
Marked differences in C/P ratios were observed in the POM: high ratios in the northern diluted waters and low in the more saline waters and in the central Adriatic. 相似文献
105.
106.
H. Wingfors . Sjdin P. Haglund E. Brorstrm-Lundn 《Atmospheric environment (Oxford, England : 1994)》2001,35(36)
The concentrations of semi-volatile polycyclic aromatic hydrocarbons (PAHs), hydrocarbons (HCs), particulate matter (PM 1, 2.5 and 10 μm) and total suspended particles (TSPs) were measured in a traffic tunnel in Gothenburg, Sweden. Emission factors (EFs) were also calculated. These variables are assumed to provide good estimates of average vehicle emissions, since all types of vehicle, using all types of fuel, pass through this tunnel. It was shown that the majority of particle-associated PAHs were found on particles with an aerodynamic diameter of <1 μm. The concentrations of PAHs were one order higher in magnitude in air samples from the tunnel than in air samples at two urban locations. However, the PAH profiles of air samples from the tunnel and the urban sites were similar. This was demonstrated using principal component analysis (PCA). Finally, and notably, there was no significant change in the total emissions when the proportion of heavy-duty vehicles (HDVs) increased from 8% to 24%. Previously, diesel vehicles had been found to release larger quantities of PAHs and related substances. Advances in fuel quality, and HDV motor and exhaust system design during the last decade may have contributed to this promising result. However, it was shown, using partial least squares regression to latent structures (PLS), that some of the parameters measured displayed correlations with the proportions of HDVs and light-duty vehicles (LDVs). Concentrations of total HCs, TSPs, dibenzothiopene, phenantrene, anthracene and monomethyl-derivatives of phenantrene and anthracene were all correlated to the proportion of HDVs. The concentrations of naphthalene, some mono- and dimethylnaphthalenes and most large PAHs (with 5–7 fused rings) were correlated to the proportion of LDVs. 相似文献
107.
广州地区大气能见度与颗粒物关系的初探 总被引:2,自引:0,他引:2
采用番禺大气成分站2007—2013年的能见度、颗粒物(PM1、PM2.5、PM10)及番禺气象局站的相对湿度(RH)资料,对颗粒物7年来的变化状况进行了分析。以RH为标准,将能见度和颗粒物数据分为RH≥90%、80%RH90%和RH≤80%3个部分,并以相关系数(R2)为判断标准,分别对其之间的相关性进行了分析。结果表明,PM10、PM2.5、PM1多年日平均值分别为56.6、43.0、38.5μg/m3,颗粒物值旱季高于雨季。当RH≤80%时,颗粒物与能见度的相关性最好,R2大小顺序为:PM10(0.47)PM2.5(0.57)PM1(0.58);当80%RH90%时,颗粒物与能见度的相关性次之,分别为PM10(0.4)PM2.5(0.46)PM1(0.49);当RH≥90%时,颗粒物与能见度的相关性较差。 相似文献
108.
Yanqing Duan Aijuan Zhou Xiuping Yue Zhichun Zhang Yanjuan Gao Yanhong Luo Xiao Zhang 《Frontiers of Environmental Science & Engineering》2021,15(1):12
109.
颗粒物激光雷达在大气复合污染立体监测中的应用 总被引:4,自引:4,他引:0
针对由于局地污染、沙尘输入、外源性输入与局地污染物相互叠加所导致的3种灰霾污染发生过程,分别选取3个典型案例,采用颗粒物激光雷达对污染物的时空分布特征进行解析。研究发现,在局地污染发生时,污染物从地面开始垂直向上扩散,扩散高度约1 km。重度污染过程中,气溶胶的日均垂直消光系数随高度的变化背离指数衰减特征,800 m高度处出现消光系数的极大值层,极大值超过2.5 km-1,800 m以下消光系数近乎常数,约为0.3 km-1。这说明,重污染过程中,有一层较厚重的颗粒物分布,使近地面污染物在垂直方向的扩散能力减弱,形成积累效应,造成大面积空气混浊。当有外源性沙尘输入时,激光雷达能够清晰地监测到污染团输入的全过程。沙团突然出现在高空2~3 km。污染团退偏振度较大,超过0.3。随着沙尘粒子的重力沉降,沙团的轮廓在垂直方向上不断地增大。沙团的输入,导致近地面粗颗粒质量浓度的增加幅度明显大于细颗粒。在第3个案例中,激光雷达清晰地监测到高空1.8~3 km突然出现含有大量球形细颗粒的污染团,同时还发现此污染团与近地面的污染物有不同的演化特征。近地面污染物随时间垂直向上扩散,12:00左右扩散高度超过1.8 km。而高空的污染团逐渐沉降进入边界层内,与近地面扩散的污染物相互混合,共同导致本地的灰霾天气。综上所述,激光雷达可以清晰地捕获污染物的垂直结构特征,对不同的致霾过程进行立体解析,实现对大气复合污染的监测和机理研判。 相似文献
110.
Yuanhang Zhang Haichao Wang Keding Lu Zhaofeng Tan Xiaorui Chen Yuhan Liu 《环境科学学报(英文版)》2023,123(1):476-486
Over the past decade, fine particulate matter (PM) pollution in China has been abated significantly, benefiting from strict emission control measures, but particulate nitrate continues to rise. Here, we review the progress in particulate nitrate (pNO3−) pollution characterization, nitrate formation mechanisms, and the proposed control strategies in China. The spatial and temporal distributions of pNO3− are summarized. The current status of knowledge on the chemical mechanism is updated, and the significance of its formation pathways is assessed by various approaches such as field observation and modelling of nitrate production rate, as well as isotopic analysis. The factors impacting pNO3− formation and the corresponding pollution regulation strategies are discussed, in which the importance of atmospheric oxidation capacity and ammonia are addressed. Finally, the challenges and open questions in pNO3− pollution control in China are outlined. 相似文献