Isokinetic Sampler for Continuous Airborne Aerosol Measurements

For aerosol measurements, especially those concerned with the aerosol particle size distribution, it is important to sample in isokinetic conditions. Most available instrumentation for aerosol measurements is intended for use on the ground under light wind conditions; intake air speeds rarely exceed a few meters per second. If the same instrumentation is used onboard an aircraft, the air must be decelerated 60 or more m/sec before It is sampled by individual instruments.

On The Pennsylvania State University Meteorology research aircraft, the air for all aerosol instruments is decelerated in a single isokinetic sampler located above the roof of the cabin outside the aircraft boundary layer. The air enters the sampler through a carefully designed circular intake. Its velocity is reduced as the cross section increases along a 7° conical diffuser. The expansion cone terminates in a cylindrical chamber in which the air velocity is 1/16 the aircraft speed. Behind the sampling chamber the air is accelerated in a second conical section to an end exhaust port. Exhaust porf "pumping" is used to compensate internal losses and, thus, helps preserve the isokinetic nature of the sampler.

Tubes leading to individual instruments are located in the sampling chamber and may be individually adapted to match the air sampling velocity with the local air speed inside the sampling chamber. The level of turbulence (u_rms/û) in the sampling section is =^0.05.

The sampler has been thoroughly wind tunnel and flight tested and successfully used in August and November, 1974, for field programs in the St. Louis and Tucson metropolitan areas, respectively.     

Odor Determination Techniques for Air Pollution Control

Abstract

An airborne lidar was used to study the smoke plume from the burning of a controlled oil spill on the ocean. The ratio of the amount of light (at a wavelength, λ, of 0.532 u.m) backscattered by the smoke to the amount of light extinguished by the smoke was determined by measuring the strength of a laser beam after it had passed through the smoke plume, been reflected from the ocean, and passed through the smoke plume again, and comparing this to the strength of the laser beam reflected directly from the ocean. The optical depth of the smoke (at λ = 0.532 µm) was typically between 0.2 and 0.5. The mass fluxes of smoke particles that passed through four vertical cross sections of the (nonsteady state) smoke plume were estimated from lidar measurements to be 142, 175, 423, and 414 g ^s-1, compared to an average smoke mass production rate of ~770 g s^-1. The spatial distribution of smoke mass along the long axis of the plume was also estimated from the lidar measurements; derived smoke mass concentrations were generally <300 µg ^m-3, with a few isolated values up to ~800 µg ^m-3.     

Control of Organic Emissions from Surface Coating Operations

ABSTRACT

Step tracer tests were carried out on lab-scale biofilters to determine the residence time distributions (RTDs) of gases passing through two types of biofilters: a standard biofilter with vertical gas flow and a modified biofilter with horizontal gas flow. Results were used to define the flow patterns in the reactors. “Non-ideal flow” indicates that the flow reactors did not behave like either type of ideal reactor: the perfectly stirred reactor [often called a "continuously stirred tank reactor" (CSTR)] or the plug-flow reactor.

The horizontal biofilter with back-mixing was able to accommodate a shorter residence time without the usual requirement of greater biofilter surface area for increased biofiltration efficiency. Experimental results indicated that the first bed of the modified biofilter behaved like two CSTRs in series, while the second bed may be represented by two or three CSTRs in series. Because of the flow baffles used in the horizontal biofilter system, its performance was more similar to completely mixed systems, and hence, it could not be modeled as a plug-flow reactor. For the standard biofilter, the number of CSTRs was found to be between 2 and 9 depending on the airflow rate. In terms of NH₃ removal efficiency and elimination capacity, the standard biofilter was not as good as the modified system; moreover, the second bed of the modified biofilter exhibited greater removal efficiency than the first bed. The elimination rate increased as biofilter load increased. An opposite trend was exhibited with respect to removal efficiency.     

Large‐Scale Fine‐Resolution Hydrological Modeling Using Parameter Regionalization in the Missouri River Basin

This study simulated crop and water yields in the Missouri River Basin (MRB; 1,371,000 km²), one of the largest river basins in the United States, using the Soil and Water Assessment Tool (SWAT) at a fine resolution of 12‐digit Hydrological Unit Codes (HUCs) using the regionalization calibration approach. Very few studies have simulated the entire MRB, and those that have developed were at a coarser resolution of 8‐digit HUCs and were minimally calibrated. The MRB was first divided into three subbasins and was further divided into eleven regions. A “head watershed” was selected in each region and was calibrated for crop and water yields. The parameters from the calibrated head watershed were extrapolated to other subwatersheds in the region to complete comprehensive spatial calibration. The simulated crop yields at the head watersheds were in close agreement with observed crop yields. Spatial validation of the aggregated crop yields resulted in reasonable predictions for all crops except dryland corn in a few regions. Simulated and observed water yields in head watersheds and also in the validation locations were in close agreement in naturalized streams and poor agreement in streams with high groundwater‐surface water interactions and/or reservoirs found upstream of the gauges. Overall, the SWAT model was able to reasonably capture the hydrological and crop growth dynamics occurring in the basin despite some limitations.     

From Global to Local: Providing Actionable Flood Forecast Information in a Cloud‐Based Computing Environment

Global and continental scale flood forecast provide coarse resolution flood forecast, but from the perspective of emergency management, flood warnings should be detailed and specific to local conditions. The desired refinement can be provided by the use of downscaling global scale models and through the use of distributed hydrologic models to produce a high‐resolution flood forecast. Three major challenges associated with transforming global flood forecasting to a local scale are addressed in this work. The first is using open‐source software tools to provide access to multiple data sources and lowering the barriers for users in management agencies at local level. This can be done through the Tethys Platform that enables web water resources modeling applications. The second is finding a practical solution for the computational requirements associated with running complex models and performing multiple simulations. This is done using Tethys Cluster that manages distributed and cloud computing resources as a companion to the Tethys Platform for web app development. The third challenge is discovering ways to downscale the forecasts from the global extent to the local context. Three modeling strategies have been tested to address this, including downscaling of coarse resolution global runoff models to high‐resolution stream networks and routing with Routing Application for Parallel computatIon of Discharge (RAPID), the use of hierarchical Gridded Surface and Subsurface Hydrologic Analysis (GSSHA) distributed models, and pre‐computed distributed GSSHA models.     

Comparison of total mercury and methylmercury cycling at five sites using the small watershed approach

The small watershed approach is well-suited but underutilized in mercury research. We applied the small watershed approach to investigate total mercury (THg) and methylmercury (MeHg) dynamics in streamwater at the five diverse forested headwater catchments of the US Geological Survey Water, Energy, and Biogeochemical Budgets (WEBB) program. At all sites, baseflow THg was generally less than 1ng L(-1) and MeHg was less than 0.2ng L(-1). THg and MeHg concentrations increased with streamflow, so export was primarily episodic. At three sites, THg and MeHg concentration and export were dominated by the particulate fraction in association with POC at high flows, with maximum THg (MeHg) concentrations of 94 (2.56)ng L(-1) at Sleepers River, Vermont; 112 (0.75)ng L(-1) at Rio Icacos, Puerto Rico; and 55 (0.80)ng L(-1) at Panola Mt., Georgia. Filtered (<0.7microm) THg increased more modestly with flow in association with the hydrophobic acid fraction (HPOA) of DOC, with maximum filtered THg concentrations near 5ng L(-1) at both Sleepers and Icacos. At Andrews Creek, Colorado, THg export was also episodic but was dominated by filtered THg, as POC concentrations were low. MeHg typically tracked THg so that each site had a fairly constant MeHg/THg ratio, which ranged from near zero at Andrews to 15% at the low-relief, groundwater-dominated Allequash Creek, Wisconsin. Allequash was the only site with filtered MeHg consistently above detection, and the filtered fraction dominated both THg and MeHg. Relative to inputs in wet deposition, watershed retention of THg (minus any subsequent volatilization) was 96.6% at Allequash, 60% at Sleepers, and 83% at Andrews. Icacos had a net export of THg, possibly due to historic gold mining or frequent disturbance from landslides. Quantification and interpretation of Hg dynamics was facilitated by the small watershed approach with emphasis on event sampling.     

Comparison of speciation sampler and PC-BOSS fine particulate matter organic material results obtained in Lindon, Utah, during winter 2001-2002

The Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) has been previously verified as being capable of measuring total fine particulate matter (PM2.5), including semi-volatile species. The present study was conducted to determine if the simple modification of a commercial speciation sampler with a charcoal denuder followed by a filter pack containing a quartz filter and a charcoal-impregnated glass (CIG) fiber filter would allow for the measurement of total PM2.5, including semi-volatile organic material. Data were collected using an R&P (Rupprecht and Pastasnik Co., Inc.) Partisol Model 2300 speciation sampler; an R&P Partisol speciation sampler modified with a BOSS denuder, followed by a filter pack with a quartz and a CIG filter; a Met One spiral aerosol speciation sampler (SASS); and the PC-BOSS from November 2001 to March 2002 at a U.S. Environmental Protection Agency (EPA) Science to Achieve Results (STAR) sampling site in Lindon, UT. Total PM2.5 mass, ammonium nitrate (both nonvolatile and semi-volatile), ammonium sulfate, organic carbon (both non-volatile and semi-volatile), and elemental carbon were determined on a 24-hr basis. Results obtained with the individual samplers were compared to determine the capability of the modified R&P speciation sampler for measuring total PM2.5, including semi-volatile components. Data obtained with the modified speciation sampler agreed with the PC-BOSS results. Data obtained with the two unmodified speciation samplers were low by an average of 26% because of the loss of semi-volatile organic material from the quartz filter during sample collection.     

Measurement of fine particulate matter nonvolatile and semi-volatile organic material with the Sunset Laboratory Carbon Aerosol Monitor

Semi-volatile organic material (SVOM) in fine particles is not reliably measured with conventional semicontinuous carbon monitors because SVOM is lost from the collection media during sample collection. We have modified a Sunset Laboratory Carbon Aerosol Monitor to allow for the determination of SVOM. In a conventional Sunset monitor, gas-phase organic compounds are removed in the sampled airstream by a diffusion denuder employing charcoal-impregnated cellulose filter (CIF) surfaces. Subsequently, particles are collected on a quartz filter and the instrument then determines both the organic carbon and elemental carbon fractions of the aerosol using a thermal/optical method. However, some of the SVOM is lost from the filter during collection, and therefore is not determined. Because the interfering gas-phase organic compounds are removed before aerosol collection, the SVOM can be determined by filtering the particles at the instrument inlet and then replacing the quartz filter in the monitor with a charcoal-impregnated glass fiber filter (CIG), which retains the SVOM lost from particles collected on the inlet filter. The resulting collected SVOM is then determined in the analysis step by measurement of the carbonaceous material thermally evolved from the CIG filter. This concept was tested during field studies in February 2003 in Lindon, UT, and in July 2003 in Rubidoux, CA. The results obtained were validated by comparison with Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) results. The sum of nonvolatile organic material determined with a conventional Sunset monitor and SVOM determined with the modified Sunset monitor agree with the PC-BOSS results. Linear regression analysis of total carbon concentrations determined by the PC-BOSS and the Sunset resulted in a zero-intercept slope of 0.99 +/- 0.02 (R2 = 0.92) and a precision of sigma = +/- 1.5 microg C/m3 (8%).     

Transplantation of the Subshrub Lotus scoparius: Testing the Home-Site Advantage Hypothesis

Abstract: The long-term success of restored populations may be jeopardized by the collection locality of transplants if they are ill matched to their new environment. The home-site advantage hypothesis predicts that the relative success of introduced populations will decrease as their genetic and environmental distance to the local native population increases. We evaluated this hypothesis for a geographically variable shrub, Lotus scoparius , in southern Californian coastal sage scrub by planting two common-garden experiments with seedlings from 12 source populations. The common-garden sites differed in environment and were each home to different source populations of the two taxonomic varieties, L. s. var. scoparius or L. s . var. brevialatus . We used allozyme data from each source population to calculate genetic distances between populations, and a combination of climatic data and soil traits to calculate environmental distances. At the more mesic, coastal common garden, cumulative fitness of transplants (survival × flower production) was inversely related to genetic distance between source and resident populations. At the more xeric, inland common garden, cumulative fitness (survival × size) decreased significantly with both genetic and environmental distance after one taxonomic variety was excluded from analyses. Geographic distance was only weakly correlated with genetic distance and had little value in predicting cumulative fitness of transplants. Our data support the home-site advantage hypothesis and the idea that mis-matching source populations of these genetically differentiated seed sources may result in lowered success of restored or constructed populations. The genetic and environmental similarities of source populations should be considered when source materials are chosen for transplantation.     

酸化湖泊水生生物恢复的理论框架构建

在欧洲和北美广大地区,随着大气硫沉降的减少,地表水体酸度正在逐渐降低,但是对水质改善的生态响应过程却依然扑朔迷离.有些湖泊和河流的生物正在恢复,有些水体的生物并没有得到恢复.为理解这些生物响应的差异,有利于酸雨问题的有效管理,我们需要对下面2个问题有清晰的认识:①生物群落恢复所必须经历的生态步骤;②倘若恢复受阻,从哪里着手对恢复进程实施干预,如何干预.本文通过构建一套理论框架来回答上述问题.第一层框架是基于生态学考虑而构建的,通过决策树来反映生态恢复进程中必须经历的若干步骤,步骤之间则通过管理工具或对瓶颈的响应来连接.水质不佳,移生生物供给不足以建群,以及群落水平上对恢复动态变化的阻碍等等都可能成为恢复的瓶颈所在.第二层框架则是基于管理层次来构建的,为了克服瓶颈,框架指明从哪里着手对恢复进程实施干预,为建模来进一步将框架具体化,需要做哪些研究.一旦我们可以用模型来预测酸化水体生态恢复的速率和程度,对硫排放减少带来的效益评价就变得简单起来.而这些模型的构建需要充分认识恢复进程中的生态步骤.本文提出的理论框架将有助于我们朝这个目标迈进.