Relevant Mixing Ratios Research Articles

Relative Humidity Impact on Organic New Particle Formation from Ozonolysis of α- and β-Pinene at Atmospherically Relevant Mixing Ratios

The impact of relative humidity (RH) on organic new particle formation (NPF) from ozonolysis of monoterpenes remains an area of active debate. Previous reports provide contradictory results indicating both depression and enhancement of NPF under conditions of moderate RH, while others do not indicate a potential impact. Only several reports have suggested that the effect may depend on absolute mixing ratio of the precursor volatile organic compound (VOC, ppbv). Herein we report on the impact of RH on NPF from dark ozonolysis of α- and β-pinene at mixing ratios ranging from 0.2 to 80 ppbv. We show that RH enhances NPF (by a factor of eight) at the lowest α-pinene mixing ratio, with a very strong dependence on α-pinene mixing ratio from 4 to 22 ppbv. At higher mixing ratios, the effect of RH plateaus, with resulting modest decreases in NPF. In the case of α- and β-pinene, NPF is enhanced at low mixing ratios due to a combination of chemistry, accelerated kinetics, and reduced partitioning of semi-volatile oxidation products to the particulate phase. Reduced partitioning would limit particle growth, permitting increased gas-phase concentrations of semi- and low-volatility products, which could favor NPF.

A portable, robust, stable, and tunable calibration source for gas-phase nitrous acid (HONO)

Abstract. Atmospheric HONO mixing ratios in indoor and outdoor environments span a range of less than a few parts per trillion by volume (pptv) up to tens of parts per billion by volume (ppbv) in combustion plumes. Previous HONO calibration sources have utilized proton transfer acid displacement from nitrite salts or solutions, with output that ranges from tens to thousands of ppbv. Instrument calibrations have thus required large dilution flows to obtain atmospherically relevant mixing ratios. Here we present a simple universal source to reach very low HONO calibration mixing ratios using a nitrite-coated reaction device with the addition of humid air and/or HCl from a permeation device. The calibration source developed in this work can generate HONO across the atmospherically relevant range and has high purity (> 90 %), reproducibility, and tunability. Mixing ratios at the tens of pptv level are easily reached with reasonable dilution flows. The calibration source can be assembled to start producing stable HONO mixing ratios (relative standard error, RSE ≤ 2 %) within 2 h, with output concentrations varying ≤ 25 % following simulated transport or complete disassembly of the instrument and with ≤ 10 % under ideal conditions. The simplicity of this source makes it highly versatile for field and lab experiments. The platform facilitates a new level of accuracy in established instrumentation, as well as intercomparison studies to identify systematic HONO measurement bias and interferences.

Y-Site Physical Compatibility of Numeta G13E with Drugs Frequently Used at Neonatal Intensive Care.

Preterm neonates require parenteral nutrition (PN) in addition to intravenous drug therapy. Due to limited venous access, drugs are often co-administered with PN via the same lumen. If incompatible, precipitation and emulsion destabilization may occur with the consequent risk of embolism and hyper-immune reactions. Information on intravenous compatibility is scarce. Our aim was to analyse the compatibility of Numeta G13E with paracetamol, vancomycin and fentanyl because of the frequency of their use. A panel of methods was chosen to assess precipitation (sub-visual particle counting, turbidity measurement, Tyndall beam effect and pH measurement) and emulsion destabilization (mean droplet diameter measurement and sub-visual counting of oil droplets, followed by estimation of PFAT5 (percentage of fat residing in globules larger than 5 µm) and pH measurement). Samples in clinically relevant mixing ratios were tested immediately and after 4 h. All samples of drugs mixed with Numeta G13E were compared to unmixed controls. None of the tested drugs precipitated in contact with Numeta G13E, and we did not see any sign of emulsion destabilization when clinically relevant mixing ratios were applied. These results are reassuring. However, when contact time exceeds the established norm, caution in the form of filter utilisation and close inspection is advised.

Environmentally relevant mixing ratios in cumulative assessments: A study of the kinetics of pyrethroids and their ester cleavage metabolites in blood and brain; and the effect of a pyrethroid mixture on the motor activity of rats

National surveys of United States households and child care centers have demonstrated that pyrethroids are widely distributed in indoor habited dwellings and this suggests that co-exposure to multiple pyrethroids occurs in nonoccupational settings. The purpose of this research was to use an environmentally relevant mixture of pyrethroids to assess their cumulative effect on motor activity and develop kinetic profiles for these pyrethroids and their hydrolytic metabolites in brain and blood of rats. Rats were dosed orally at one of two levels (1.5× or 5.0× the calculated dose that decreases rat motor activity by 30%) with a mixture of cypermethrin, deltamethrin, esfenvalerate, cis-/trans-permethrin, and β-cyfluthrin in corn oil. At 1, 2, 4, 8, or 24h after dosing, the motor activity of each animal was assessed and the animals sacrificed. Concentrations of pyrethroids in brain and blood, and the following metabolites: cis-/trans-dichlorovinyl-dimethylcyclopropane-carboxylic acid, 3-phenoxybenzoic acid, 3-phenoxybenzyl alcohol, 4-fluoro-3-phenoxybenzoic acid, and cis-dibromovinyl-dimethylcyclopropane-carboxylic acid were determined using liquid chromatography tandem mass spectrometry (LC–MS/MS). Using this pyrethroid mixture in rats, the results suggest there is greater metabolism of trans-permethrin prior to entering the systemic circulatory system. All pyrethroids had tissue half-lives (t1/2) of less than 5h, excepting esfenvalerate in brain. At early time points, relative pyrethroid brain concentrations approximated their dose mixture proportions and a sigmoidal Emax model described the relationship between motor activity decrease and total pyrethroid brain concentration. In blood, the t1/2's of the cyclopropane metabolites were longer than the phenoxybenzoic metabolites. However, relative to their respective precursors, concentrations of the phenoxybenzoic acids were much higher than concentrations of the cyclopropane metabolites. Brain concentrations of all metabolites were low relative to blood concentrations. This implies limited metabolite penetration of the blood-brain barrier and little metabolite formation within the brain. In conclusion: toxicokinetic differences between the pyrethroids did not appear to be important determinants of their relative potency and their effect on motor activity was consistent with a pyrethroid dose additive model.

Oxidation of C60 Aerosols by Atmospherically Relevant Levels of O3

Atmospheric processing of carbonaceous nanoparticles (CNPs) may play an important role in determining their fate and environmental impacts. This work investigates the reaction between aerosolized C60 and atmospherically relevant mixing ratios of O3 at differing levels of humidity. Results indicate that C60 is oxidized by O3 and forms a variety of oxygen-containing functional groups on the aerosol surface, including C60O, C60O2, and C60O3. The pseudo-first-order reaction rate between C60 and O3 ranges from 9 × 10(-6) to 2 × 10(-5) s(-1). The reaction is likely to be limited to the aerosol surface. Exposure to O3 increases the oxidative stress exerted by the C60 aerosols as measured by the dichlorofluorescein acellular assay but not by the uric acid, ascorbic acid, glutathione, or dithiothreitol assays. The initial prevalence of C60O and C60O2 as intermediate products is enhanced at higher humidity, as is the surface oxygen content of the aerosols. These results show that C60 can be oxidized when exposed to O3 under ambient conditions, such as those found in environmental, laboratory, and industrial settings.

Testing for Additivity at Select Mixture Groups of Interest Based on Statistical Equivalence Testing Methods

Several assumptions, defined and undefined, are used in the toxicity assessment of chemical mixtures. In scientific practice mixture components in the low-dose region, particularly subthreshold doses, are often assumed to behave additively (i.e., zero interaction) based on heuristic arguments. This assumption has important implications in the practice of risk assessment, but has not been experimentally tested. We have developed methodology to test for additivity in the sense of Berenbaum (Advances in Cancer Research, 1981), based on the statistical equivalence testing literature where the null hypothesis of interaction is rejected for the alternative hypothesis of additivity when data support the claim. The implication of this approach is that conclusions of additivity are made with a false positive rate controlled by the experimenter. The claim of additivity is based on prespecified additivity margins, which are chosen using expert biological judgment such that small deviations from additivity, which are not considered to be biologically important, are not statistically significant. This approach is in contrast to the usual hypothesis-testing framework that assumes additivity in the null hypothesis and rejects when there is significant evidence of interaction. In this scenario, failure to reject may be due to lack of statistical power making the claim of additivity problematic. The proposed method is illustrated in a mixture of five organophosphorus pesticides that were experimentally evaluated alone and at relevant mixing ratios. Motor activity was assessed in adult male rats following acute exposure. Four low-dose mixture groups were evaluated. Evidence of additivity is found in three of the four low-dose mixture groups. The proposed method tests for additivity of the whole mixture and does not take into account subset interactions (e.g., synergistic, antagonistic) that may have occurred and cancelled each other out.

Power and Sample Size Calculations for Linear Hypotheses Associated with Mixtures of Many Components using Fixed-Ratio Ray Designs

Response surface methodology, often supported by factorial designs, is the classical experimental approach that is widely accepted for detecting and characterizing interactions among chemicals in a mixture. In an effort to reduce the experimental effort as the number of compounds under study is increased, ray designs have been proposed to study combinations of chemicals. When interest is restricted to relevant mixing ratios, we are only interested in making inference along the specific rays of interest, as opposed to methods which use designs that require more experimental effort to support the estimation of a response surface over a broader experimental region. Methods have been developed for the test of additivity along multiple fixed-ratio rays. Of primary importance is the detection of interactions with reasonable power. The objective of this paper is to address power and sample size issues related to the hypothesis of no interaction.

Consistency of Ozone and Nitrogen Oxides Standards at Tropospherically Relevant Mixing Ratios

The absolute accuracy and long‐term precision of atmospheric measurements hinge on the quality of the instrumentation and calibration standards. To assess the consistency of the ozone (O3) and nitrogen oxides (NOx) standards maintained at the National Institute of Standards and Technology (NIST), these standards were compared through the gas‐phase titration of O3 with nitric oxide (NO). NO and O3 were monitored using chemiluminescence and UV absorption, respectively. Nitrogen dioxide (NO2) was monitored directly by laser‐induced fluorescence and indirectly by catalytic conversion to NO, followed by chemiluminescence. The observed equivalent loss of both NO and O3 and the formation of NO2 in these experiments was within 1% on average over the range of 40–200 nmol mol−1 of NO in excess O3, indicating that these instruments, when calibrated with the NIST O3 and NO standards and the NO2 permeation calibration system, are consistent to within 1% at tropospherically relevant mixing ratios of O3. Experiments conducted at higher initial NO mixing ratios or in excess NO are not in as good agreement. The largest discrepancies are associated with the chemiluminescence measurements. These results indicate the presence of systematic biases under these specific conditions. Prospects for improving these experiments are discussed.

Ds-optimal designs for studying combinations of chemicals using multiple fixed-ratio ray experiments

Detecting and characterizing interactions among chemicals is an important environmental issue. Traditional factorial designs become infeasible as the number of compounds under study increases. Ray designs, which reduce the amount of experimental effort, can be considered when interest is restricted to relevant mixing ratios. Simultaneous tests for departure from additivity across multiple fixed-ratio rays in the presence and absence of single chemical data have been developed. Tests for characterizing interactions among subsets of chemicals at relevant mixing ratios have also been developed. Of primary importance are precise estimates for the parameters associated with these hypotheses. Since the hypotheses of interest are stated in terms of subsets of parameters, we have developed a methodology for finding Ds-optimal designs, which are associated with the minimum generalized variance of subsets of the parameter vector, along fixed-ratio rays. We illustrate these methods by characterizing the interactions of five organophosphorus pesticides (full-ray) as well as a subset of pesticides (reduced-ray) on a measure of motor activity. Copyright © 2004 John Wiley & Sons, Ltd.

An analysis of the distribution of nitrogen dioxide in the south-eastern Mediterranean for the period 1985–1989

Abstract The abundance of ozone in the stratosphere depends upon a photochemical cycle in which nitrogen dioxide ( N02) plays a predominant role. Although the zonal mean cross-sections for N02 averaged for 34 months have been calculated–on the basis of L1MS data–lack of detailed information at local or regional scale could result in difficulties in terms of modelling the distribution of ozone in the stratosphere. In this paper we use SAGE II measurements to calculate the altitude profiles of N02 mixing ratios for the geographical region 15 to 30° E and 32·5 to 42·5° N for the period 1985 to 1989.Analysis of the findings shows that N02 experiences higher values in summer months, that the N02 maximum mixing ratios decrease from 1985 to 1989, that maximum mixing ratios are found at an altitude ofapproximately 33 km, with variations depending on season and year and that N02 mixing ratios for the period 1985–1989 are higher compared to the relevant mixing ratios for 1979–1981.