Time filter

Source Type

Emeryville, CA, United States

Simmons C.E.,ENVIRON International Corporation
Journal of occupational and environmental hygiene | Year: 2011

Sanding drywall joint compound is a dusty construction activity. We studied potential factors influencing exposure to respirable and total dust for sanders and bystanders in the area of drywall joint compound finishing in 17 test events within a room-scale isolation chamber. We found the air change rate to be negatively correlated with dust C(twa) both in the sander's personal breathing zone and surrounding area. We could not conclude that sanding tool type systematically influences dust C(twa), but the use of 80-grit abrasive was associated with the highest dust C(twa). We found respirable dusts were uniformly dispersed 1-8.2 m from sanding activities at a fixed location. As anticipated, both respirable and total dust C(twa) in the sander's personal breathing zone are higher than in the surrounding area. The respirable fraction of the total dust mass C(twa) was greater in the surrounding area than in the sander's personal breathing zone. Respirable dust concentrations measured in real time increased over the duration of sanding, exhibiting a temporal trend that is similar to that predicted by the well-mixed box model with contaminant removal by mechanical ventilation only, and continuous emission. Dust concentrations returned to pre-activity (background) levels 2-4 hr after cessation of the sanding activity. Source

Zhou B.,ENVIRON International Corporation | Du J.,National Oceanic and Atmospheric Administration
Weather and Forecasting | Year: 2010

A new multivariable-based diagnostic fog-forecasting method has been developed at NCEP. The selection of these variables, their thresholds, and the influences on fog forecasting are discussed. With the inclusion of the algorithm in the model postprocessor, the fog forecast can now be provided centrally as direct NWP model guidance. The method can be easily adapted to other NWP models. Currently, knowledge of how well fog forecasts based on operational NWP models perform is lacking. To verify the new method and assess fog forecast skill, as well as to account for forecast uncertainty, this fog-forecasting algorithm is applied to a multimodel-based Mesoscale Ensemble Prediction System (MEPS). MEPS consists of 10 members using two regional models [the NCEP Nonhydrostatic Mesoscale Model (NMM) version of the Weather Research and Forecasting (WRF) model and the NCAR Advanced Research version of WRF (ARW)] with 15-km horizontal resolution. Each model has five members (one control and four perturbed members) using the breeding technique to perturb the initial conditions and was run once per day out to 36 h over eastern China for seven months (February-September 2008). Both deterministic and probabilistic forecasts were produced based on individual members, a one-model ensemble, and two-model ensembles. A case study and statistical verification, using both deterministic and probabilistic measuring scores, were performed against fog observations from 13 cities in eastern China. The verification was focused on the 12- and 36-h forecasts. By applying the various approaches, including the new fog detection scheme, ensemble technique, multimodel approach, and the increase in ensemble size, the fog forecast accuracy was steadily and dramatically improved in each of the approaches: from basically no skill at all [equitable threat score (ETS) 5 0.063] to a skill level equivalent to that of warm-season precipitation forecasts of the current NWP models (0.334). Specifically, 1) the multivariable-based fog diagnostic method has a much higher detection capability than the liquid water content (LWC)-only based approach. Reasons why the multivariable approach works better than the LWC-only method were also illustrated. 2) The ensemble-based forecasts are, in general, superior to a single control forecast measured both deterministically and probabilistically. The case study also demonstrates that the ensemble approach could provide more societal value than a single forecast to end users, especially for low-probability significant events like fog. Deterministically, a forecast close to the ensemble median is particularly helpful. 3) The reliability of probabilistic forecasts can be effectively improved by using a multimodel ensemble instead of a single-model ensemble. For a small ensemble such as the one in this study, the increase in ensemble size is also important in improving probabilistic forecasts, although this effect is expected to decrease with the increase in ensemble size. © 2010 American Meteorological Society. Source

Rodricks J.V.,ENVIRON International Corporation
Human and Ecological Risk Assessment | Year: 2014

The publication in 1962 of Rachel Carson's Silent Spring marks the mid-point in a century that saw, in its first half, the emergence of public health concerns related to human exposures to chemicals, and, in its second half, the emergence of public policies to deal with those concerns. Those policies made it imperative that the scientific community come to grips with the problem of identifying exposure levels not likely to cause harm. This problem was not significantly discussed within the scientific community until the 1950s, and well-described methods for practical solutions to it did not appear until the 1970s. An important report from the National Academy of Sciences, published in 1983 (Risk Assessment in the Federal Government), provided an analysis of these emerging methods, and recommended a useful framework for the assessment and management of risk. This framework remains central to public health and regulatory decision-making. A high-level perspective is offered on events leading to and following the 1983 report. The article describes early thinking about chemical toxicity and the scientific path that thinking followed through the 20th century, and to the present. © 2014 Copyright Taylor and Francis Group, LLC. Source

Sarwar G.,U.S. Environmental Protection Agency | Simon H.,U.S. Environmental Protection Agency | Bhave P.,U.S. Environmental Protection Agency | Yarwood G.,ENVIRON International Corporation
Atmospheric Chemistry and Physics | Year: 2012

The heterogeneous hydrolysis of dinitrogen pentoxide (N+ADw-inf+AD4-2+ADw-/ inf+AD4-O+ADw-inf+AD4-5+ADw-/inf+AD4-) has typically been modeled as only producing nitric acid. However, recent field studies have confirmed that the presence of particulate chloride alters the reaction product to produce nitryl chloride (ClNO+ADw-inf+AD4-2+ADw-/inf+AD4-) which undergoes photolysis to generate chlorine atoms and nitrogen dioxide (NO+ADw-inf+AD4-2+ADw-/inf+AD4-). Both chlorine and NO+ADw-inf+AD4-2+ADw-/inf+AD4- affect atmospheric chemistry and air quality. We present an updated gas-phase chlorine mechanism that can be combined with the Carbon Bond 05 mechanism and incorporate the combined mechanism into the Community Multiscale Air Quality (CMAQ) modeling system. We then update the current model treatment of heterogeneous hydrolysis of N+ADw-inf+AD4-2+ADw-/inf+AD4-O+ADw-inf+AD4-5+ADw-/inf+AD4- to include ClNO+ADw-inf+AD4-2+ADw-/inf+AD4- as a product. The model, in combination with a comprehensive inventory of chlorine compounds, reactive nitrogen, particulate matter, and organic compounds, is used to evaluate the impact of the heterogeneous ClNO+ADw-inf+AD4-2+ADw-/inf+AD4- production on air quality across the United States for the months of February and September in 2006. The heterogeneous production increases ClNO+ADw-inf+AD4-2+ADw-/inf+AD4- in coastal as well as many in-land areas in the United States. Particulate chloride derived from sea-salts, anthropogenic sources, and forest fires activates the heterogeneous production of ClNO+ADw-inf+AD4-2+ADw-/inf+AD4-. With current estimates of tropospheric emissions, it modestly enhances monthly mean 8-h ozone (up to 1-2 ppbv or 3-4+ACU-) but causes large increases (up to 13 ppbv) in isolated episodes. This chemistry also substantially reduces the mean total nitrate by up to 0.8-2.0 +ACY-mu+ADs-g m+ADw-sup+AD4--3+ADw-/sup+AD4- or 11-21+ACU-. Modeled ClNO+ADw-inf+AD4-2+ADw-/inf+AD4- accounts for up to 6+ACU- of the monthly mean total reactive nitrogen. Sensitivity results of the model suggest that heterogeneous production of ClNO+ADw-inf+AD4-2+ADw-/inf+AD4- can further increase O+ADw-inf+AD4-3+ADw-/inf+AD4- and reduce TNO+ADw-inf+AD4-3+ADw- /inf+AD4- if elevated particulate-chloride levels are present in the atmosphere. © Author(s) 2012. Source

Gauthier T.D.,ENVIRON International Corporation
Analytical Chemistry Insights | Year: 2013

1,3-Dimethylamylamine (1,3-DMAA) is an aliphatic amine with stimulant properties that are reportedly found naturally only in geranium plants (Pelargonium graveolens). The presence of 1,3-DMAA in geranium plants was first reported in a paper published in 1996, but some have questioned the identification of 1,3-DMAA in that study. Since then, a number of additional studies have been published, largely reporting the absence of 1,3-DMAA in geranium plants and commercial geranium oils. However, in two recent studies, 1,3-DMAA was detected in geranium plant tissues and a geranium oil sample using a simplified extraction approach on tissues and oil sourced from China. Whether or not 1,3-DMAA is found naturally in plants has significant implications as to how commercial products containing 1,3-DMAA are regulated by the US Food and Drug Administration. In this paper, differences in source materials, extraction procedures, and analytical approaches are reviewed in an attempt to rationalize the apparently conflicting evidence for the presence of 1,3-DMAA in geranium plant materials. © the author(s), publisher and licensee Libertas Academica Ltd. Source

Discover hidden collaborations