Comparison and Evaluation of Chemically Speciated Mobile Source PM2.5 Particulate Matter Profiles

ABSTRACT

Mobile sources are significant contributors to ambient PM_{2 5}, accounting for 50% or more of the total observed levels in some locations. One of the important methods for resolving the mobile source contribution is through chemical mass balance (CMB) receptor modeling. CMB requires chemically speciated source profiles with known uncertainty to ensure accurate source contribution estimates. Mobile source PM profiles are available from various sources and are generally in the form of weight fraction by chemical species. The weight fraction format is commonly used, since it is required for input into the CMB receptor model. This paper examines the similarities and differences in mobile source PM_2.5 profiles that contain data for elements, ions, elemental carbon (EC) and organic carbon (OC), and in some cases speciated organics (e.g., polycyclic aromatic hydrocarbons [PAHs]), drawn from four different sources.

Notable characteristics of the mass fraction data include variability (relative contributions of elements and ions) among supposedly similar sources and a wide range of average EC:OC ratios (0.60 ± 0.53 to 1.42 ± 2.99) for light-duty gasoline vehicles (LDGVs), indicating significant EC emissions from LDGVs in some cases. For diesel vehicles, average EC:OC ratios range from 1.09 ± 2.66 to 3.54 ± 3.07. That different populations of the same class of emitters can show considerable variability suggests caution should be exercised when selecting and using profiles in source apportionment studies.     

Maximum Ground-Level Concentrations with Downwash—Analysis

ABSTRACT

Equations derived previously for critical downwind distance x , wind speed u , and plume rise z , the values that produce maximum ground-level concentrations (MGLC) X_c under downwash conditions, have been solved. Tables of %_c, x_c, u_c, and z_c, and graphs of the relationships among u_c and z_c for a range of stack heights h_s, and building heights h_b, are presented. Results for two types of sources— a turbine and a reciprocating engine—are discussed. Some comparisons are made to the U.S. Environmental Protection Agency's (EPA) SCREEN3 model.     

Ozone Air Quality over North America: Part II—An Analysis of Trend Detection and Attribution Techniques

ABSTRACT

Assessment of regulatory programs aimed at improving ambient O₃ air quality is of considerable interest to the scientific community and to policymakers. Trend detection, the identification of statistically significant long-term changes, and attribution, linking change to specific clima-tological and anthropogenic forcings, are instrumental to this assessment. Detection and attribution are difficult because changes in pollutant concentrations of interest to policymakers may be much smaller than natural variations due to weather and climate. In addition, there are considerable differences in reported trends seemingly based on similar statistical methods and databases. Differences arise from the variety of techniques used to reduce nontrend variation in time series, including mitigating the effects of meteorology and the variety of metrics used to track changes. In this paper, we review the trend assessment techniques being used in the air pollution field and discuss their strengths and limitations in discerning and attributing changes in O₃ to emission control policies.     

Ozone Air Quality over North America: Part I—A Review of Reported Trends

ABSTRACT

Ozone and precursor trends can be used to measure the effectiveness of regulatory programs that have been implemented. In this paper, we review trends in the concentrations of O₃, NO_x, and HCs over North America that have been reported in the literature. Although most existing trend studies are confounded by meteorological variability, both the raw data trends and the trends adjusted for meteorology collectively indicate a general decreasing trend in O concentrations in most areas of the United States during 1985-1996. In Canada, mean daily maximum 1-hr O₃ concentrations at urban sites show mixed trends with a majority of sites showing an increase from 1980 to 1993. Mean daily maximum 1-hr O₃ at most regionally representative Canadian sites appears to decrease from 1985 to 1993 or shows no significant change. There are far fewer data and analyses of NO_x and HC trends. Available studies covering various ranges of years indicate decreases in ambient NO_x and HC concentrations in Los Angeles, CA, decreases in HC concentrations in northeastern U.S. cities, and decreases in NO concentrations in Canadian cities. Two key needs are long-term HC and NO_x measurements, particularly at rural sites, and a systematic comparison of trend detection techniques on a reference data set.     

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.     

Live diatoms as indicators of urban stormwater runoff

Diatom bioassessment of streams/rivers does not distinguish between live (cells with intact chloroplasts) and dead (empty cells) individuals, even though most diatom samples collected from the field will be composed of a mixture of both. This study aimed to evaluate whether percentage of live diatoms (PLD), live diatom density and chlorophyll a, and diatom species compositions can be used as indicators of hydrologic disturbance in an urban stream. We deployed artificial substrates on a monthly basis and collected periphyton samples weekly over the course of one calendar year (n = 182) in three tributaries of urbanized Ruddiman Creek (Michigan, USA). We also collected samples before and after six major storm events (>0.5 cm rain). We found no temporal patterns in PLD (Mann-Kendall test p > 0.05) or species composition (non-metric multidimensional scaling (NMDS) ordination), which may be explained by a diatom composition already tolerant to frequent disturbance. There was no difference in PLD before and after storm events, which might partially be explained by their disturbance resistance due to different assemblage ages (1, 2, and 4 weeks old) before the storms. High flow had differential effects on diatom species; loosely attached Navicula and Nitzschia species were more easily removed compared to stalk-forming Gomphonema parvulum. The most important environmental variable that was found to affect live diatom density and chlorophyll was stream width, which has an indirect effect (as a measure of discharge) on periphyton assemblages. In conclusion, PLD was found to be unsuitable metric for assessing stormwater runoff in urban streams where periphyton may not have enough time to form mature communities.     

Oxygen transfer in a full-depth biological aerated filter

The City of San Diego, California, evaluated the performance capabilities of biological aerated filters (BAFs) at the Point Loma Wastewater Treatment Plant. The City conducted a 1-year pilot-plant evaluation of BAF technology supplied by two BAF manufacturers. This paper reports on the first independent oxygen-transfer test of BAFs at full depth using the offgas method. The tests showed process-water oxygen-transfer efficiencies of 1.6 to 5.8%/m (0.5 to 1.8%/ft) and 3.9 to 7.9%/m (1.2 to 2.4%/ft) for the two different pilot plants, at their nominal design conditions. Mass balances using chemical oxygen demand and dissolved organic carbon corroborated the transfer rates. Rates are higher than expected from fine-pore diffusers for similar process conditions and depths and clean-water conditions for the same column and are mostly attributed to extended bubble retention time resulting from interactions with the media and biofilm.     

Multibiomarker approach in fish to assess the impact of pollution in a large Brazilian river, Paraiba do Sul

This article examines the advantages of the use of biomarkers as environmental indicators by applying it to Paraiba do Sul watershed, one of the most important Brazilian water bodies, which is in a critical environmental situation. We use a multibiomarker approach in fish as an integrated strategy to assess the impact of pollution. It comprehends a general biomarker of fish health, the condition factor (CF), and specific biomarkers of contaminant exposure such as metallothionein (MT), acetylcholinesterase (AChE) activity and biliary polycyclic aromatic hydrocarbons (PAH) metabolites. Our results revealed different effects in the fish from diverse locations with varying degrees of pollution. Furthermore, fish located just upstream of the water-treatment plant of the metropolitan area of Rio de Janeiro has shown to be affected by metals. This study indicates the usefulness of integrating a set of biomarkers to define the effects of anthropogenic inputs in aquatic bodies under complex polluted situations.