Richard E. Peltier

Viscous flow models of global geophysical observables: 1. Forward problems

We present a gravitationally consistent method for calculating the “kernel” functions which relate global geophysical observables, such as the geoid, surface plate motions and core-mantle boundary (CMB) topography, to internal density heterogeneities in a viscous, compressible mantle possessing an arbitrary radial variation of viscosity. We show that the influence of finite mantle compressibility is substantial in the case of the predicted nonhydrostatic geoid, with the largest effects occurring at spherical harmonic degree l=2. On the basis of the geoid data we find that our best two-layer viscosity model possesses a factor of 9 jump in viscosity at 1200 km depth. We argue, however, that the inferences of viscosity obtained from the geoid data are sensitive to the model of internal density heterogeneity which is employed and that this sensitivity probably explains the differences between our own viscosity inferences and those obtained by others. Our viscous flow models possess a spherically symmetric viscosity distribution and they cannot therefore “explain” the toroidal component of the flow of the tectonic plates. We therefore present a new scheme for predicting plate motions based on an explicit coupling of poloidal and toroidal flows which we derive on the basis of the assumption that the individual plates are perfectly rigid. We show how this new description of surface plate motions induced by buoyancy forces in the mantle may be used to constrain the absolute value of the long-term (i.e., steady state) mantle viscosity.

Airborne measurements of carbonaceous aerosol soluble in water over northeastern United States: Method development and an investigation into water-soluble organic carbon sources

[1] A particle-into-liquid sampler (PILS) was coupled to a total organic carbon (TOC) analyzer for 3 s integrated measurements of water-soluble organic carbon (WSOC) in PM1 ambient particles. The components of the instrument are described in detail. The PILS-TOC was deployed on the NOAA WP-3D aircraft during the NEAQS/ITCT 2004 program to investigate WSOC sources over the northeastern United States and Canada. Two main sources were identified: biomass burning emissions from fires in Alaska and northwestern Canada and emissions emanating from urban centers. Biomass burning WSOC was correlated with carbon monoxide (CO) and acetonitrile (r 2 > 0.88). These plumes were intercepted in layers at altitudes between 3 and 4 km and contained the highest fine particle volume and WSOC concentrations of the mission. Apart from the biomass burning influence, the lowest WSOC concentrations were recorded in rural air masses that included regions of significant biogenic emissions. Highest concentrations were at low altitudes in distinct plumes from urban centers. WSOC and CO were highly correlated (r 2 > 0.78) in these urban plumes. The ratio of the enhancement in WSOC relative to CO enhancement was found to be low (� 3 mg C/m 3 /ppmv) in plumes that had been in transit for a short time, and increased with plume age, but appeared to level off at � 32 ± 4 mg C/m 3 /ppmv after � 1 day of transport from the sources. The results suggest that the production of WSOC in fine particles depends on compounds coemitted with CO and that this process is rapid with a time constant of � 1 day.

Sources of particulate matter in the northeastern United States in summer: 1. Direct emissions and secondary formation of organic matter in urban plumes

[1] Ship and aircraft measurements of aerosol organic matter (OM) and water-soluble organic carbon (WSOC) were made in fresh and aged pollution plumes from major urban areas in the northeastern United States in the framework of the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) study. A large part of the variability in the data was quantitatively described by a simple parameterization from a previous study that uses measured mixing ratios of CO and either the transport age or the photochemical age of the sampled air masses. The results suggest that OM was mostly due to secondary formation from anthropogenic volatile organic compound (VOC) precursors in urban plumes. Approximately 37% of the secondary formation can be accounted for by the removal of aromatic precursors using newly published particulate mass yields for low-NOx conditions, which are significantly higher than previous results. Of the secondary formation, 63% remains unexplained and is possibly due to semivolatile precursors that are not measurable by standard gas chromatographic methods. The observed secondary OM in urban plumes may account for 35% of the total source of OM in the United States and 8.5% of the global OM source. OM is an important factor in climate and air quality issues, but its sources and formation mechanisms remain poorly quantified.

Organic aerosols associated with the generation of reactive oxygen species (ROS) by water-soluble PM2.5

We compare the relative toxicity of various organic aerosol (OA) components identified by an aerosol mass spectrometer (AMS) based on their ability to generate reactive oxygen species (ROS). Ambient fine aerosols were collected from urban (three in Atlanta, GA and one in Birmingham, AL) and rural (Yorkville, GA and Centerville, AL) sites in the Southeastern United States. The ROS generating capability of the water-soluble fraction of the particles was measured by the dithiothreitol (DTT) assay. Water-soluble PM extracts were further separated into the hydrophobic and hydrophilic fractions using a C-18 column, and both fractions were analyzed for DTT activity and water-soluble metals. Organic aerosol composition was measured at selected sites using a high-resolution time-of-flight AMS. Positive matrix factorization of the AMS spectra resolved the organic aerosol into isoprene-derived OA (Isop_OA), hydrocarbon-like OA (HOA), less-oxidized oxygenated OA, (LO-OOA), more-oxidized OOA (MO-OOA), cooking OA (COA), and biomass burning OA (BBOA). The association of the DTT activity of water-soluble PM2.5 (WS_DTT) with these factors was investigated by linear regression techniques. BBOA and MO-OOA were most consistently linked with WS_DTT, with intrinsic water-soluble activities of 151 ± 20 and 36 ± 22 pmol/min/μg, respectively. Although less toxic, MO-OOA was most widespread, contributing to WS_DTT activity at all sites and during all seasons. WS_DTT activity was least associated with biogenic secondary organic aerosol. The OA components contributing to WS_DTT were humic-like substances (HULIS), which are abundantly emitted in biomass burning (BBOA) and include highly oxidized OA from multiple sources (MO-OOA). Overall, OA contributed approximately 60% to the WS_DTT activity, with the remaining probably from water-soluble metals, which were mostly associated with the hydrophilic WS_DTT fraction.

No evidence for acid‐catalyzed secondary organic aerosol formation in power plant plumes over metropolitan Atlanta, Georgia

Aircraft-based measurements of the water-soluble fraction of fine PM organic carbon (WSOC) and inorganic salt composition in the Atlanta, GA region were conducted in the summer of 2004. Five notable plumes of SO{sub 2}, apparently from coal-fired power plants, were intercepted, and had NH{sub 4}{sup +}/SO4{sup 2-} molar ratios ranging from approximately 0.8 to 1.4 compared to molar ratios near 2 outside of the plumes. Sulfate aerosol concentrations increased from a regional background of 5 - 8 {mu} g m{sup -3} to as high as 19.5 {mu} g m{sup -3} within these plumes. No increase in WSOC concentrations was observed in plumes compared to out-of-plumes within a WSOC measurement uncertainty of 8%. These measurements suggest that secondary organic aerosol formation via heterogeneous acid-catalyzed reactions within power plant plumes are not likely a significant contributor to the ambient aerosol mass loading in Atlanta and the surrounding region. Because this region is rich in both biogenic and anthropogenic volatile organic carbon (VOC), the results may be widely applicable.

Residual oil combustion: 2. Distributions of airborne nickel and vanadium within New York City

In an earlier paper based on PM2.5 speciation network data, we showed that nickel (Ni) concentrations were much higher in New York City (NYC) than in New Jersey (NJ) and Connecticut (CT), and that the NYC levels, but not those in NJ and CT, were much higher in the winter than in summer. However, all of the speciation sites in NYC were in the northern half of the city. To determine the distributions of Ni and other PM2.5 components within NYC, we collected 8-weeklong filter samples at 10 sites throughout NYC in both winter and summer, and measured the concentrations of the elements by X-ray fluorescence (XRF). The resulting data, together with speciation network site data, were used to construct seasonal average concentration isopleth maps for Ni and vanadium (V). As expected, Ni was much higher in Bronx than in Brooklyn, and much higher in winter than in summer. By contrast, V was higher in Brooklyn than in Bronx, and the winter and summer levels were similar. It appears that space-heating boilers are the major source category for Ni in NYC, whereas the Port of New York is the major source of V.

Residual oil combustion: a major source of airborne nickel in New York City

On the basis of previous observations that: (1) both the nickel (Ni) concentration in ambient air fine particulate matter (PM2.5) and daily mortality rates in New York City (NYC) were much higher than in any other US city; and (2) that peaks in Ni concentration was strongly associated with cardiac function in a mouse model of atherosclerosis, we initiated a study of the spatial and seasonal distributions of Ni in NYC and vicinity to determine the feasibility of productive human population-based studies of the extent to which ambient fine particle Ni may account for cardiovascular health effects. Using available speciation data from previous studies at The New York University, Environmental Protection Agencys Speciation Trends Network; and the Interagency Monitoring of Protected Visual Environments network, we determined that Ni in NYC is on average 2.5 times higher in winter than in summer. This apparent seasonal gradient is absent, or much less pronounced, at NJ and CT speciation sites. Ni concentrations at a site on the east side of Manhattan and at two sites in the western portion of the Bronx were a factor of two higher than at a site on the west side of Manhattan, or at one at Queens College in eastern Queens County, indicating a strong spatial gradient within NYC. We conclude that the winter peaks of fine particle Ni indicate that space heating, which involves the widespread reliance on residual oil combustion in many older residential and commercial buildings in NYC, is a major source of ambient air Ni. Epidemiologic studies based on data generated by a network of speciation sites throughout NYC could effectively test the hypothesis that Ni could account for a significant portion of the excess mortality and morbidity that have been associated with elevated mass concentrations of PM2.5.

Investigating a Liquid-Based Method for Online Organic Carbon Detection in Atmospheric Particles

A Particle-Into-Liquid Sampler (PILS) was modified and coupled with a Total Organic Carbon (TOC) Analyzer (Sievers 800T, GE Water Systems, Boulder, CO), in an attempt to measure particulate organic carbon (OC) online. The PILS droplet collection system was changed from an inertial impactor to a miniature cyclone to increase the efficiency of transferring insoluble carbonaceous aerosol to the liquid sample stream. The performance of the modified PILS was investigated with a variety of calibration aerosols through comparison with the Sunset Labs ECOC technique (NIOSH method 5040). Linear regression slopes of water-soluble organic compounds compared well with Sunset Labs measurement, agreeing to within 5%. However, a size dependence was observed when comparing insoluble carbonaceous aerosol (polystyrene latex spheres, PSL). The new method did not effectively measure insoluble particles with aerodynamic diameters greater than ∼ 110 nm due to inefficient analysis by the TOC. The OC measurement method was also compared with online Sunset Labs organic carbon (OC) measurements in two urban locations: Atlanta, GA, and Riverside, CA. Linear regression slopes between the PILS technique and Sunset Labs were near unity (101% to 93% ± 2 and 5%, respectively), and not statistically different from unity considering the measurement uncertainty of each method. However there was a significant (0.6 to 1.7 μ gC m − 3 ) non-zero intercept, with the Sunset Labs instrument measuring higher concentrations, possible due to the inability of the PILS to measure large, insoluble particles or positive artifacts with the non-blank corrected Sunset Labs filter-based collection method.

Exposure to particulate matter in India: A synthesis of findings and future directions.

Air pollution poses a critical threat to human health with ambient and household air pollution identified as key health risks in India. While there are many studies investigating concentration, composition, and health effects of air pollution, investigators are only beginning to focus on estimating or measuring personal exposure. Further, the relevance of exposures studies from the developed countries in developing countries is uncertain. This review summarizes existing research on exposure to particulate matter (PM) in India, identifies gaps and offers recommendations for future research. There are a limited number of studies focused on exposure to PM and/or associated health effects in India, but it is evident that levels of exposure are much higher than those reported in developed countries. Most studies have focused on coarse aerosols, with a few studies on fine aerosols. Additionally, most studies have focused on a handful of cities, and there are many unknowns in terms of ambient levels of PM as well as personal exposure. Given the high mortality burden associated with air pollution exposure in India, a deeper understanding of ambient pollutant levels as well as source strengths is crucial, both in urban and rural areas. Further, the attention needs to expand beyond the handful large cities that have been studied in detail.

Spatial and seasonal distribution of aerosol chemical components in New York City: (2) road dust and other tracers of traffic-generated air pollution.

We describe spatial and temporal patterns of seven chemical elements commonly observed in fine particulate matter (PM) and thought to be linked to roadway emissions that were measured at residential locations in New York City (NYC). These elements, that is, Si, Al, Ti, Fe, Ba, Br, and black carbon (BC), were found to have significant spatial and temporal variability at our 10 residential PM2.5 sampling locations. We also describe pilot study data of near-roadway samples of both PM10−2.5 and PM2.5 chemical elements of roadway emissions. PM2.5 element concentrations collected on the George Washington Bridge (GWB) connecting NYC and New Jersey were higher that similar elemental concentration measured at residential locations. Coarse-particle elements (within PM10−2.5) on the GWB were 10–100 times higher in concentration than their PM2.5 counterparts. Roadway elements were well correlated with one another in both the PM2.5 and PM10−2.5 fractions, suggesting common sources. The same elements in the PM2.5 collected at residential locations were less correlated, suggesting either different sources or different processing mechanisms for each element. Despite the fact that these elements are only a fraction of total PM2.5 or PM10−2.5 mass, the results have important implications for near-roadway exposures where elements with known causal links to health effects are shown to be at elevated concentrations in both the PM2.5 and PM10−2.5 size ranges.