122 research outputs found
Spark ignition vehicle contributions to atmospheric fine elemental carbon concentrations in coastal, rural and urban communities using polycyclic aromatic hydrocarbon tracers in the CMB model modified for reactivity
We apportioned the elemental carbon (EC) component of ambient PM2.5 attributable to emissions from spark ignition (SI) vehicles in samples collected over a three-year period in twelve Southern California communities, including coastal, rural, and urban areas using the chemical mass balance model (CMB8) modified for polycyclic aromatic hydrocarbon (PAH) reactivity. Selected PAH/EC ratios, measured in samples collected in the Caldecott tunnel were evaluated for use as fingerprints. PAH reactivity which occurs during atmospheric transport and affects the source contribution estimates during the summer/fall/spring months was accounted for using experimentally measured decay constants. Results showed that benzo[ghi]perylene and indeno[1,2,3-cd]pyrene can be used successfully as specific tracers of EC contributions from SI vehicles. The average EC portion of PM2.5 attributed by the model to SI emissions at these communities was 39, 58 and 62%, respectively, during the summer, spring/autumn, and winter. For all seasons, coastal community contributions represent about twice those found in the rural and urban inland communities, before December 2003 when MTBE was still in use in California
Chemical and Biological Characterization of Particulate Matter (PM 2.5) and Volatile Organic Compounds Collected at Different Sites in the Los Angeles Basin
Background: Most studies on air pollution (AP) exposure have focused on adverse health effects of particulate matter (PM). Less well-studied are the actions of volatile organic compounds (VOCs) not retained in PM collections. These studies quantified chemical and biological properties of both PM2.5 and VOCs. Methods: Samples were collected near the Port of Los Angeles (Long Beach, LB), railroads (Commerce, CM), and a pollution-trapping topography-site (San Bernardino, SB). Quantitative assays were conducted: (1) chemicalâprooxidant and electrophile content, (2) biologicalâtumor necrosis factor-α (TNF-α) and heme oxygenase-1 (HO-1) expression (3), VOC modulation of PM effects and (4), activation of the antioxidant response element (ARE) using murine RAW 264.7 macrophages. Results: SB site samples were the most potent in the chemical and biological assays, followed by a CM railroad site. Only PM2.5 exhibited significant proinflammatory responses. VOCs were more potent than PM2.5 in generating anti-inflammatory responses; further, VOC pretreatment reduced PM-associated TNF-α expression. VOCs significantly increased ARE activation compared to their corresponding PM2.5 which remained at background levels. Conclusion: Ambient VOCs are major contributors to adaptive responses that can modulate PM effects, in vitro, and, as such, need to be included in comprehensive assessments of AP
Sources, concentrations, and risks of naphthalene in indoor and outdoor air
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92148/1/j.1600-0668.2011.00760.x.pd
SOA formation from naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene photooxidation
Chemical reactivity and long-range transport potential of polycyclic aromatic hydrocarbons â a review
Polycyclic aromatic hydrocarbons (PAHs) are of considerable concern due to their well-recognised toxicity and especially due to the carcinogenic hazard which they present. PAHs are semi-volatile and therefore partition between vapour and condensed phases in the atmosphere and both the vapour and particulate forms undergo chemical reactions. This article briefly reviews the current understanding of vapour-particle partitioning of PAHs and the PAH deposition processes, and in greater detail, their chemical reactions. PAHs are reactive towards a number of atmospheric oxidants, most notably the hydroxyl radical, ozone, the nitrate radical (NO3) and nitrogen dioxide. Rate coefficient data are reviewed for reactions of lower molecular weight PAH vapour with these species as well as for heterogeneous reactions of higher molecular weight compounds. Whereas the data for reactions of the 2-3-ring PAH vapour are quite extensive and generally consistent, such data are mostly lacking for the 4-ring PAHs and the heterogeneous rate data (5 and more rings), which are dependent on the substrate type and reaction conditions, are less comprehensive. The atmospheric reactions of PAH lead to the formation of oxy and nitro derivatives, reviewed here, too. Finally, the capacity of PAHs for long range transport and the results of numerical model studies are described. Research needs are identified
An online monitor of the oxidative capacity of aerosols (o-MOCA)
The capacity of airborne particulate matter to generate reactive oxygen
species (ROS) has been correlated with the generation of oxidative stress
both in vitro and in vivo. The cellular damage from oxidative stress, and by
implication with ROS, is associated with several common diseases, such as
asthma and chronic obstructive pulmonary disease (COPD), and some neurological
diseases. Yet currently available chemical and in vitro assays to
determine the oxidative capacity of ambient particles require large samples,
analyses are typically done offline, and the results are not immediate.Here we report the development of an online
monitor of the oxidative capacity of
aerosols (o-MOCA) to provide online, time-resolved assessment of
the capacity of airborne particles to generate ROS. Our approach combines
the Liquid Spot Sampler (LSS), which collects particles directly into small
volumes of liquid, and a chemical module optimized for online measurement
of the oxidative capacity of aerosol using the dithiothreitol (DTT) assay.
The LSS uses a three-stage, laminar-flow water condensation approach to
enable the collection of particles as small as 5âŻnm into liquid. The DTT
assay has been improved to allow the online, time-resolved analysis of
samples collected with the LSS but could be adapted to other collection
methods or offline analysis of liquid extracts.The o-MOCA was optimized and its performance evaluated using the
9,10-phenanthraquinone (PQ) as a standard redox-active compound. Laboratory
testing shows minimum interferences or carryover between consecutive
samples, low blanks, and a reproducible, linear response between the DTT
consumption rate (nmolâŻminâ1) and PQ concentration (”M). The calculated
limit of detection for o-MOCA was 0.15âŻnmolâŻminâ1. The system was validated
with a diesel exhaust particle (DEP) extract, previously characterized and
used for the development, improvement, and validation of the standard DTT
analysis. The DTT consumption rates (nmolâŻminâ1) obtained with the o-MOCA were
within experimental uncertainties of those previously reported for these DEP
samples. In ambient air testing, the fully automated o-MOCA was run
unattended for 3 days with 3âŻh time resolution and showed a diurnal and
daily variability in the measured consumption rates (nmolâŻminâ1âŻmâ3)
Design and Laboratory Evaluation of a Sequential Spot Sampler for Time-Resolved Measurement of Airborne Particle Composition
Time-resolved characterization of particle associated polycyclic aromatic hydrocarbons using a newly-developed sequential spot sampler with automated extraction and analysis
Detection of sub-5nm naturally charged carbonaceous materials from a sooting laminar premixed flame by a water condensation Particle Counter (WCPC) enhanced by a Di-Ethylene Glycol (DEG) saturator inlet
International audienceCombustion is one of the major contributors to air pollution and Condensation Particle Counters (CPCs) provide effective monitoring of atmospheric aerosols since they can detect both charged and neutral materials in low number concentrations. The detection efficiency of any CPC for materials smaller than 5ânm requires ad-hoc calibrations because it is affected by the analyteâs size, shape, charge state, composition, and wettability by the condensing fluid. This study characterizes a Water-based CPC (WCPC) prototype for the detection of the naturally charged carbonaceous products of an incipiently sooting laminar premixed flame. The WCPC can activate condensation growth and (50% efficient) detection of hydrophobic flame-formed carbonaceous materials naturally charged in positive and negative polarities with mobility diameters as small as 4.3ânm and 4.8ânm, respectively. The addition of a simple Di-Ethylene Glycol (DEG) saturator inlet enhances the 50% detection cutoff to mobility diameters as small as 1.8ânm or 1.6ânm for materials charged in positive or negative polarity, respectively. The coupling of the DEG saturator inlet to the WCPC creates a new DEG-WCPC instrument able to detect efficiently both hydrophobic and hydrophilic sub-5nm aerosols with a marginal increase in manufacturing cost (<10%), dimensions, and weight (<0.25âkg)
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