Hygroscopic organic aerosols during BRAVO?

The hygroscopic properties of the organic fraction of aerosols are poorly understood. The ability of organic aerosols to absorb water as a function of relative humidity (RH) was examined using data collected during the 1999 Big Bend Regional Aerosol and Visibility Observational Study (BRAVO). (On average, organics accounted for 22% of fine particulate matter with an aerodynamic diameter less than 2.5 microm (PM2.5) mass). Hourly RH exceeded 80% only 3.5% of the time and averaged 44%. BRAVO aerosol chemical composition and dry particle size distributions were used to estimate PM2.5 light scattering (Bsp) at low and high ambient RH. Liquid water growth associated with inorganic species was sufficient to account for measured Bsp for RH between 70 and 95%.     

Spatial, temporal, and interspecies patterns in fine particulate matter in Texas

The Big Bend Regional Aerosol and Visibility Observational (BRAVO) field study was conducted from July to October 1999 and was followed by several years of modeling and data analyses to examine the causes of haze at Big Bend National Park TX (BBNP). During BRAVO, daily speciated fine (diameter <2.5 microm) particulate concentrations were measured at 37 sites throughout Texas. At the primary receptor site, K-Bar Ranch, there were many additional measurements including a "high-sensitivity" version of the 24-hr fine particulate elemental data. The spatial, temporal, and interspecies patterns in these data are examined here to qualitatively investigate source regions and source types influencing the fine particulate concentrations in Texas with an emphasis on sources of sulfates, the largest contributor to fine mass and light extinction. Peak values of particulate sulfur (S) varied spatially and seasonally. Maximum S was in Northeast Texas during the summer, whereas peak S at BBNP was in the fall. Sulfate acidity at BBNP also varied by month. Sources of Se were evident in Northeast Texas and from the Carbón I and II plants. High S episodes at BBNP during BRAVO had several different trace element characteristics. Carbon concentrations at BBNP during BRAVO were probably mostly urban-related, with arrival from the Houston area likely. The Houston artificial tracer released during the second half of BRAVO was highly correlated with some carbon fractions. There was evidence of the influence of African dust at sites throughout Texas during the summer. Patterns in several trace elements were also examined. Vanadium was associated with air masses from Mexico. Lead concentrations in southern Texas have dropped dramatically over the past several years.     

Loss of particle nitrate from teflon sampling filters: effects on measured gravimetric mass in California and in the IMPROVE network

The extent of mass loss on Teflon filters caused by ammonium nitrate volatilization can be a substantial fraction of the measured particulate matter with an aerodynamic diameter less than 2.5 microm (PM2.5) or 10 microm (PM10) mass and depends on where and when it was collected. There is no straightforward method to correct for the mass loss using routine monitoring data. In southern California during the California Acid Deposition Monitoring Program, 30-40% of the gravimetric PM2.5 mass was lost during summer daytime. Lower mass losses occurred at more remote locations. The estimated potential mass loss in the Interagency Monitoring of Protected Visual Environments network was consistent with the measured loss observed in California. The biased mass measurement implies that use of Federal Reference Method data for fine particles may lead to control strategies that are biased toward sources of fugitive dust, other primary particle emission sources, and stable secondary particles (e.g., sulfates). This analysis clearly supports the need for speciated analysis of samples collected in a manner that preserves volatile species. Finally, although there is loss of volatile nitrate (NO3-) from Teflon filters during sampling, the NO3- remaining after collection is quite stable. We found little loss of NO3- from Teflon filters after 2 hr under vacuum and 1 min of heating by a cyclotron proton beam.     

Analysis of Respirable Fractions in Atmospheric Particulates via Sequential Filtration

It has long been recognized that information on particle size distributions in atmospheric aerosals is necessary for meaningful evaluations of potential health hazards. Such information is also important in establishing particulate sources, transport, transformations, and sinks, especially in combination with elemental and chemical data. While instruments exist to collect size segregated samples of particulates, they are too complex and expensive to encourage use of multiple units in field situations.     

Evaluation of Wind Fields Used in Grand Canyon Visibility Transport Commission Analyses

ABSTRACT

The Grand Canyon Visibility Transport Commission (GCVTC) was established by the U.S. Congress to assess the potential impacts of projected growth on atmospheric visibility at Grand Canyon National Park and to make recommendations to the U.S. Environmental Protection Agency on what measures could be taken to avoid such adverse impacts. A critical input to the assessment tool used by the commission was three-dimensional model-derived wind fields used to transport the emissions. This paper describes the evaluation of the wind fields used at various stages in the assessment. Wind fields evaluated included those obtained from the Colorado State University Regional Atmospheric Modeling System (RAMS), the National Meteorological Center's Nested Grid Model (NGM), and the National Oceanic and Atmospheric Administration's Atmospheric Transport and Dispersion (ATAD) trajectory model. The model-derived wind fields were evaluated at multiple vertical levels at several locations in the southwestern United States by determining differences between model predicted winds and winds that were measured using radiosonde and radar wind profiler data. Model-derived winds were also evaluated by determining the percent of time that they were within acceptable differences from measured winds.

All models had difficulties, generally meeting the acceptable criteria for less than 50% of the predictions. The RAMS model had a persistent bias toward southwesterly winds at the expense of other directions, especially failing to represent channeling by north-south mountain ranges in the lower levels. The NGM model exhibited a substantial bias in the summer months by extending northwesterly winds in the eastern Pacific Ocean well inland, in contrast to the observed southwesterlies at inland locations. The simpler ATAD trajectory model performed somewhat better than the other models, probably because of its use of more upper air sites. The results of the evaluation indicated that these wind fields could not be used to reliably predict source-receptor impacts on a particular day; thus, seasonally averaged impacts were used in the GCVTC assessment.     

我国湖泊营养物基准的制定方法研究

湖泊富营养化的程度日益严重,已经对人类的生产生活、水生动植物的生存造成了危害。西方一些发达国家尤其是美国已经制定了水体水质基准,形成了一系列的基准制定的方法体系,建立了水质的管理体制。文章描述了我国的湖泊富营养化的现状、美国营养物基准的研究进展;列举了几个能够辅助基准制定的数学模型,探讨了我国的湖泊富营养化基准的制定方法步骤;通过几种模型的比较,并结合我国各方面的特点,确定我国基准制定中参照状态向基准的转化方法以及基准模型的应用和成果。     

Evaluation of filter-based aerosol measurements during the 1987 Southern California Air Quality Study

The Southern California Air Quality Study (SCAQS) was conducted during the summer and fall of 1987 to assess the causes of elevated ozone and suspended particulate matter concentrations in California's South Coast Air Basin (SoCAB). Extensive gaseous (i.e. nitric acid, ammonia, sulfur dioxide) and particle (i.e. PM_2.5 and PM₁₀ mass, elements, ions, carbon) measurements were acquired for 11 days during the summer at nine locations, and six days during the fall at six locations. Outliers were identified so that they could be excluded from further statistical analyses. Carbon and elemental measurements were found to be negatively biased by 20% owing to inhomogenous aerosol deposits on the SCAQS filters and analysis methods which were applied to a portion of the filters. These biases seem relatively consistent, however, and should not affect conclusions drawn from data analysis efforts if they are appropriately considered. Significant fractions (30–60%) of ammonium nitrate volatilized during the summer when temperatures were higher. Less than 10% typically volatilized during the fall when temperatures were lower. Anion/cation balances support the accuracy and precision estimates of the nitrate, sulfate, and ammonium measurements. Coarse particle sulfate was generally low, while coarse particle nitrate was most pronounced at the coastal sites.This paper documents SCAQS filter-based aerosol measurement methods, and evaluates the accuracy, precision, and validity of the data set. Various comparisons were made for: (1) PM_2.5/PM₁₀ ratios for mass and major chemical species; (2) sum of chemical species versus measured mass; (3) sulfate versus sulfur ratios; (4) PM_2.5 particulate nitrate versus nitric acid-denuded nitrate; and (5) anion/cation balances. The measurement and evaluation techniques presented in this paper serve as a guideline for other data analysis and modeling studies.