Abstract  BACKGROUND: Few recent studies examined acute effects on health of individual chemical species in the particulate matter (PM) mixture, and most of them have been conducted in North America. Studies in Southern Europe are scarce. The aim of this study is to examine the relationship between particulate matter constituents and daily hospital admissions and mortality in five cities in Southern Europe.

METHODS: The study included five cities in Southern Europe, three cities in Spain: Barcelona (2003-2010), Madrid (2007-2008) and Huelva (2003-2010); and two cities in Italy: Rome (2005-2007) and Bologna (2011-2013). A case-crossover design was used to link cardiovascular and respiratory hospital admissions and total, cardiovascular and respiratory mortality with a pre-defined list of 16 PM10 and PM2.5 constituents. Lags 0 to 2 were examined. City-specific results were combined by random-effects meta-analysis.

RESULTS: Most of the elements studied, namely EC, SO4(2-), SiO2, Ca, Fe, Zn, Cu, Ti, Mn, V and Ni, showed increased percent changes in cardiovascular and/or respiratory hospitalizations, mainly at lags 0 and 1. The percent increase by one interquartile range (IQR) change ranged from 0.69% to 3.29%. After adjustment for total PM levels, only associations for Mn, Zn and Ni remained significant. For mortality, although positive associations were identified (Fe and Ti for total mortality; EC and Mg for cardiovascular mortality; and NO3(-) for respiratory mortality) the patterns were less clear.

CONCLUSIONS: The associations found in this study reflect that several PM constituents, originating from different sources, may drive previously reported results between PM and hospital admissions in the Mediterranean area.

Abstract  BACKGROUND: Elevated pediatric asthma morbidity has been observed in rural US communities, but the role of the ambient environment in exacerbating rural asthma is poorly understood.

OBJECTIVES: To investigate associations between particulate matter less than 2.5μm in diameter (PM2.5) and pediatric asthma exacerbations in an agricultural community of Washington State.

METHODS: School-aged children with asthma (n=58) were followed for up to 25 months with repeated measures of respiratory health. Asthma symptoms and quick-relief medication use were assessed biweekly through phone administered surveys (n=2023 interviews). In addition, subjects used home peak flow meters on a daily basis to measure forced expiratory volume in one second (FEV1) (n=7830 measurements). Regional PM2.5 was measured at a single air monitor located centrally in the study region. To assess relationships between PM2.5 and these outcomes we used linear regression with generalized estimating equations, adjusting for meteorological and temporal confounders. Effect modification by atopy was explored as well.

RESULTS: An interquartile increase (IQR) in weekly PM2.5 of 6.7μg/m(3) was associated with an increase in reported asthma symptoms Specific symptoms including wheezing, limitation of activities, and nighttime waking displayed the strongest associations. FEV1 as a percent of predicted decreased by 0.9% (95%CI: -1.8, 0.0) for an IQR increase in PM2.5 one day prior, and by 1.4% (95%CI: -2.7, -0.2) when restricted to children with atopic asthma.

CONCLUSIONS: This study provides evidence that PM2.5 in an agricultural setting contributes to elevated asthma morbidity. Further work on identifying and mitigating sources of PM2.5 in the area is warranted.

Abstract  BACKGROUND: The prevalence of Autistic Disorder (AD), a serious developmental condition, has risen dramatically over the past two decades but high-quality population-based research addressing etiology is limited. OBJECTIVES: We studied the influence of exposures to traffic-related air pollution during pregnancy on the development of autism using data from air monitoring stations and a land use regression (LUR) model to estimate exposures. METHODS: Children of mothers who gave birth in Los Angeles who were diagnosed with a primary AD diagnosis at ages 3-5 years during 1998-2009 were identified through the California Department of Developmental Services and linked to 1995-2006 California birth certificates. For 7,603 children with autism and 10 controls per case matched by sex, birth year, and minimum gestational age, birth addresses were mapped and linked to the nearest air monitoring station and a LUR model. We used conditional logistic regression, adjusting for maternal and perinatal characteristics including indicators of SES. RESULTS: Per interquartile range (IQR) increase, we estimated a 12-15% relative increase in odds of autism for O3 (OR = 1.12, 95% CI: 1.06, 1.19; per 11.54 ppb increase) and PM2.5 (OR = 1.15, 95% CI: 1.06, 1.24; per 4.68 μg/m3 increase) when mutually adjusting for both pollutants. Furthermore, we estimated 3-9% relative increases in odds per IQR increase for LUR-based NO and NO2 exposure estimates. LUR-based associations were strongest for children of mothers with less than a high school education. CONCLUSION: Measured and estimated exposures from ambient pollutant monitors and LUR model suggest associations between autism and prenatal air pollution exposure, mostly related to traffic sources.

Abstract  A radiative transfer scheme that considers absorption, scattering, and distribution of light-absorbing elemental carbon (EC) particles collected on a quartz-fiber filter was developed to explain simultaneous filter reflectance and transmittance observations prior to and during thermal/optical analysis for carbonaceous aerosol. The model is applied to study ambient filter samples from the United States and HongKong, China, and how they differ from each other and from reference carbon black samples. Most particles in ambient samples deposit into the top half of the filter, resuspended carbon black particles are only found close to the filter surface. Pyrolized/charred organic carbon (POC) generated during thermal analysis reduces filter reflectance and transmittance in a fashion that suggests a uniform distribution of POC throughout the filter. When heated in oxygen, most EC evolves earlier than the within-filter charring for certain ambient samples. This shows the different natures of EC, and also results in an inexact optical correction to separate organic and elemental carbon by thermal analysis, especially when the POC/EC ratio is large. Particle absorption in the filter is estimated for comparisons with the EC/POC measurements, suggesting a mass absorption eDciency of ~2.7 ± 0.2 m2 (gC)?1 for reference carbon black and >15 m2 (gC)?1 for ambient EC, similar to previous estimates in the literature.

Abstract  Aerosol mass spectrometry has become an essential tool in monitoring tropospheric aerosols. Various approaches have been developed for analyzing particles that range in size from 10 nm to 10 ?m in diameter, and which consist of salts, soot, crustal matter, metals, and organic molecules, often mixed together. This wide variety of particle types has generated an equally wide variety of ionization sources, which include electron impact, laser ionization, laser desorption, chemical ionization, and electron capture ionization. Some instruments are capable of single particle analysis, while others require the collection of an ensemble of particles to obtain sufficient sample for analysis. Most instruments have been designed to ionize and analyze particular classes of compounds (e.g. salts, soot, or organics). This review provides a very broad overview of the aerosol mass spectrometry field and serves as an introduction to the many papers in this issue that deal with details about specific instruments.

Abstract  OBJECTIVE: Air pollution can promote airway inflammation, posing significant health risks for children with chronic respiratory problems. However, it is unknown whether this process is reversible, so that limiting pollution will benefit these children. We measured the short-term response of allergic asthmatic children exposed to a real-life reduction in outdoor air pollution by using noninvasive biomarkers of airway inflammation and function. PATIENTS AND METHODS: Thirty-seven untreated allergic children with mild persistent asthma were recruited from a highly polluted urban environment and relocated to a less polluted rural environment. Air pollution, pollen counts, and meteorological conditions were carefully monitored at both sites. Nasal eosinophils, fractional exhaled nitric oxide, peak expiratory flow, and urinary leukotriene E(4) were measured first in the urban environment and then again 7 days after relocation to the rural environment. RESULTS: One week after relocation to the rural environment, we measured, on average, a fourfold decrease in nasal eosinophils and significant decrease in fractional exhaled nitric oxide. We also noted an improvement in lower airway function, reflected by highly significant increase in peak expiratory flow. In contrast, mean urinary leukotriene E(4) concentration remained unchanged after 1 week of exposure to the rural environment. CONCLUSIONS: Better air quality is associated with a rapid reduction of airway inflammation in allergic asthmatic children. Nasal eosinophils and fractional exhaled nitric oxide are sensitive indicators of this effect, and their rapid decline is paralleled by improved airway function measured by peak expiratory flow. Leukotriene synthesis has a more variable response to environmental modifications.

Abstract  A parameterization of aerosol optical parameters is developed and implemented in an extended version of the community climate model version 3.2 (CCM3) of the U.S. National Center for Atmospheric Research. Direct radiative forcing (DRF) by monthly averaged calculated concentrations of non-sea-salt sulfate and black carbon (BC) is estimated. Inputs are production-specific BC and sulfate from Iversen and Seland [2002] and background aerosol size distribution and composition. The scheme interpolates between tabulated values to obtain the aerosol single scattering albedo, asymmetry factor, extinction coefficient, and specific extinction coefficient. The tables are constructed by full calculations of optical properties for an array of aerosol input values, for which size-distributed aerosol properties are estimated from theory for condensation and Brownian coagulation, assumed distribution of cloud-droplet residuals from aqueous phase oxidation, and prescribed properties of the background aerosols. Humidity swelling is estimated from the Köhler equation, and Mie calculations finally yield spectrally resolved aerosol optical parameters for 13 solar bands. The scheme is shown to give excellent agreement with nonparameterized DRF calculations for a wide range of situations. Using IPCC emission scenarios for the years 2000 and 2100, calculations with an atmospheric global cliamte model (AFCM) yield a global net anthropogenic DRF of −0.11 and 0.11 W m−2, respectively, when 90% of BC from biomass burning is assumed anthropogenic. In the 2000 scenario, the individual DRF due to sulfate and BC has separately been estimated to −0.29 and 0.19 W m−2, respectively. Our estimates of DRF by BC per BC mass burden are lower than earlier published estimates. Some sensitivity tests are included to investigate to what extent uncertain assumptions may influence these results.

Abstract  The indirect effect of anthropogenic aerosols, whereby aerosol particles change cloud optical properties, is the most uncertain component of climate forcing over the past 100 years. Here we use a mechanistic treatment of droplet nucleation and a prognostic treatment of the number of cloud droplets to study the indirect aerosol effect from changes in carbonaceous and sulfate aerosols. Cloud droplet nucleation is parameterized as a function of total aerosol number concentration, updraft velocity, and an activation parameter, which takes into account the mechanism of sulfate aerosol formation. Where previous studies focussed either on sulfate aerosols or carbonaceous aerosols only, here we estimate the combined effect. The combined indirect aerosol effect amounts to −1.1 W m−2 for an internally mixed aerosol and −1.5 W m−2 for an externally mixed aerosol compared to −1.4 W m−2, which we obtained by empirically relating sulfate mass to cloud droplet number. In the case of an internally mixed aerosol, the contribution from increasing carbonaceous and sulfate aerosols is close to being additive as the individual simulations yield an indirect effect of −0.4 W m−2 due to anthropogenic sulfate aerosols and −0.9 W m−2 due to anthropogenic carbonaceous aerosols. The contribution of anthropogenic sulfate to the indirect effect is close to zero if an externally mixed aerosol is assumed, while the contribution of carbonaceous aerosols increases to −1.3 W m−2. The effect of sulfate in the external mixture approach is much smaller than that of carbonaceous aerosols because its burden only increases by a third of that of carbonaceous aerosols and because the mode radius of sulfate is much larger than that of black and organic carbon.

Abstract  A variety of measurements have been used to evaluate the treatment of aerosol radiative properties and radiative impacts of aerosols simulated by the Model for Integrated Research on Atmospheric Global Exchange (MIRAGE). The treatment of water uptake in MIRAGE agrees with laboratory measurements, and the growth of aerosol extinction with relative humidity in MIRAGE simulations agrees with field measurements. The simulated frequency of relative humidity near 100% is about twice that of analyzed relative humidity. When the analyzed relative humidity is used to calculate aerosol water uptake in MIRAGE, the simulated aerosol optical depth agrees with most surface measurements after cloudy conditions are filtered out and differences between model and station elevations are accounted for, but simulated optical depths are too low over Brazil and central Canada. Simulated optical depths are mostly within a factor of 2 of satellite estimates, but are too high off the east coasts of the United States and China and too low off the coast of West Africa and in the Arabian Sea. The simulated single-scatter albedo is consistent with surface measurements. MIRAGE correctly simulates a larger Ångström exponent near regions with emissions of submicron particles and aerosol precursor gases, and a smaller exponent near regions with emissions of coarse particles. The simulated sensitivity of radiative forcing to aerosol optical depth is consistent with estimates from measurements. The simulated direct forcing is within the uncertainty of estimates from measurements in the North Atlantic.

Abstract  Multi-element simultaneous electrothermal atomic absorption spectrometry (ETAAS) methods were developed for determining 11 elements, in three analytical groups (group-1, predominately crustal elements, Al, Cu, Fe, Mn, and Cr; group-2, tracers of coal and oil combustion as well as other anthropogenic sources, Se, As, Pb, and Ni; and group-3, tracers of municipal incinerator aerosol–Zn and Cd), in aqueous slurry of ambient fine airborne particles, collected, at 30 min intervals with the University of Maryland–Semicontinuous Elements in Aerosol Sampler-II (SEAS-II). Combined effects of acid (0.2% v/v nitric acid) and ultrasonic treatment (15 min) improved metals recovery and slurry stability. Linear calibration ranges were improved by using a 50 mL min−1 carrier gas flow (mini-flow) during the atomization stage. However, analytical sensitivity for group-1 and 3 elements was compromised. Palladium (4 μg) and hydrogen (5% in Argon) were found to be effective modifiers for group-1 and 2 elements. A fast furnace temperature program was developed for group-3. Detection limits for the eleven marker elements by the SEAS-II-ETAA approach were compared with traditional filter X-ray fluorescence, laser ablation-ICPMS, and instrumental neutron activation analysis (INAA) techniques used in air quality studies. The efficacy of the analytical method was evaluated by analyzing interim urban PM2.5 reference material, collected in Baltimore, by the National Institute of Standards and Technology (NIST) Gaithersburg, MD. Results obtained by the ETAAS methods agreed well with the results obtained by NIST using INAA.

Abstract  We use the fractional aerosol optical depth (AOD) values derived from Multiangle Imaging Spectroradiometer (MISR) aerosol component measurements, along with aerosol transport model constraints, to estimate ground-level concentrations of fine particulate matter (PM2.5) mass and its major constituents in the continental United States. Regression models using fractional AODs predict PM2.5 mass and sulfate (SO4) concentrations in both the eastern and western United States, and nitrate (NO3) concentrations in the western United States reasonably well, compared with the available ground-level U.S. Environment Protection Agency (EPA) measurements. These models show substantially improved predictive power when compared with similar models using total-column AOD as a single predictor, especially in the western United States. The relative contributions of the MISR aerosol components in these regression models are used to estimate size distributions of EPA PM2.5 species. This method captures the overall shapes of the size distributions of PM2.5 mass and SO4 particles in the east and west, and NO3 particles in the west. However, the estimated PM2.5 and SO4 mode diameters are smaller than those previously reported by monitoring studies conducted at ground level. This is likely due to the satellite sampling bias caused by the inability to retrieve aerosols through cloud cover, and the impact of particle hygroscopicity on measured particle size distributions at ground level.

Abstract  BACKGROUND: Numerous studies have shown that ambient air pollution and smoking are both associated with increased mortality, but until now there has been little evidence as to whether the effects of these 2 factors combined are greater than the sum of their individual effects. We assessed whether smokers are subject to additional mortality risk from air pollution relative to never-smokers. METHODS: This study included 10,833 Chinese men in Hong Kong who died at the age of 30 or above during the period 1 January to 31 December 1998. Relatives who registered for deceased persons were interviewed about the deceased's smoking history and other personal lifestyle factors about 10 years before death. Poisson regression for daily number of deaths was fitted to estimate excess risks per 10 microg/m increase in particulate matter with aerodynamic diameter <10 microm (PM10) in male smokers and never-smokers in stratified data, and additional excess risk for smokers relative to never-smokers in combined data. RESULTS: In smokers there was a significant excess risk associated with PM10 for all natural causes and cardio-respiratory diseases for men age 30 years or older and men 65 or older. For all natural causes, greater excess risk associated with PM10 was observed for smokers relative to never-smokers: 1.9% (95% confidence interval = 0.3% to 3.6%) in men age 30 and older and 2.3% (0.4% to 4.3%) in those age 65 and older. CONCLUSIONS: Ambient particulate air pollution is associated with greater excess mortality in male smokers compared with never-smokers.

Abstract  Objective: It is still unknown whether specific components in fine particles are associated with heart rate variability (HRV) reduction. Methods: We recruited 46 patients with or at risk for cardiovascular diseases to measure 24-hour HRV by ambulatory electrocardiographic monitoring. Fixed-site air-monitoring stations were used to represent participants' exposures to particles with aerodynamic diameters less than 10 ?m (PM10) and 2.5 ?m (PM2.5), and particulate components of sulfate, nitrate, organic carbon (OC) and elemental carbon, and gaseous pollutants. Results: We found that HRV reduction was associated with sulfate, OC, and PM2. 5 but not with the other five pollutants in single-pollutant models. Sulfate was found to remain in significant association with HRV reduction adjusting for OC and PM2.5 in three-pollutant models. Conclusions: Exposures to sulfate and OC in PM2.5were associated with HRV reduction in patients with or at risk for cardiovascular diseases.

Abstract  Objective: The authors conducted an investigation of the association between air pollution and arrhythmia. Methods: A prospective panel study (October 2000-April 2001) was conducted in Erfurt, Germany. Fifty-seven men with coronary heart disease were subjected to six 24-hour electrocardiogram recordings. Runs of supraventricular and ventricular tachycardia were associated with continuous ultrafine particle counts (UFP), accumulation mode particle counts (ACP), PM2,5, and gaseous pollutants. Poisson and linear regression models were applied adjusting for trend, weekday, and meteorologic data. Results: Elevated concentrations of UFP, ACP, PM2,5, and nitrogen dioxide increased the risk for supraventricular runs and the number of ventricular runs at almost all lags. Statistically significant associations were found predominantly in the previous 24 to 71 hours and with the 5-day moving average. Conclusion: Elevated concentrations of fine and ultrafine particle increased the risk of arrhythmia in men with coronary heart disease.

Abstract  The National Children's Study is considering a wide spectrum of airborne pollutants that are hypothesized to potentially influence pregnancy outcomes, neurodevelopment, asthma, atopy, immune development, obesity, and pubertal development. In this article we summarize six applicable exposure assessment lessons learned from the Centers for Children's Environmental Health and Disease Prevention Research that may enhance the National Children's Study: a) Selecting individual study subjects with a wide range of pollution exposure profiles maximizes spatial-scale exposure contrasts for key pollutants of study interest. b) In studies with large sample sizes, long duration, and diverse outcomes and exposures, exposure assessment efforts should rely on modeling to provide estimates for the entire cohort, supported by subject-derived questionnaire data. c) Assessment of some exposures of interest requires individual measurements of exposures using snapshots of personal and microenvironmental exposures over short periods and/or in selected microenvironments. d) Understanding issues of spatial-temporal correlations of air pollutants, the surrogacy of specific pollutants for components of the complex mixture, and the exposure misclassification inherent in exposure estimates is critical in analysis and interpretation. e) "Usual" temporal, spatial, and physical patterns of activity can be used as modifiers of the exposure/outcome relationships. f) Biomarkers of exposure are useful for evaluation of specific exposures that have multiple routes of exposure. If these lessons are applied, the National Children's Study offers a unique opportunity to assess the adverse effects of air pollution on interrelated health outcomes during the critical early life period.

Abstract  We report on the first application of a novel fast on-road sensing method for measurement of particulate emissions of individual passing passenger cars. The study was motivated by the shift of interest from gases to particles in connection with strong adverse health effects. The results correspond very much to findings by Beaton et al. (Science, May 19,1995) for gaseous hydrocarbon and CO emissions: A small percentage of "superpolluters" (here 5%) account for a high percentage (here 43%) of the pollution (here elemental carbon). We estimate that up to 50% of the particulate emissions of vehicles could be avoided on the basis of the present legislation, if on-road monitoring would be applied to enforce maintenance. Our fast sensing method for particles is based on photoelectron emission from the emitted airborne soot particles in combination with a CO2 sensor delivering a reference.

Abstract  Background: A reliable predictor of an imminent episode of ventricular tachyarrhythmia that could be incorporated in an implantable defibrillator capable of preventive therapy would have important clinical utility. Method: A test set of 208 R–R records saved by defibrillators spanning a mean of 1.6 hours before sustained tachyarrhythmia were used to derive criteria that would improve the specificity of the previously identified monotonic heart rate acceleration predictor. Additional criteria were used, namely two such patterns need to occur within a period of 1.8 hour and the heart rate during these accelerations exceeds 86 bpm (700 ms). The specificity was tested using R–R records matched in duration from 26 control patients with defibrillators during normal periods. Results: The basic acceleration pattern was found during sinus rhythm in the 1.8-hour period prior to 83% of episodes of ventricular tachyarrhythmia. It was also found in 43% of the matched set of nonarrhythmic records, corresponding to a specificity of 57%. With the two extra requirement of multiplicity within 1.8 hour and peak heart rate, the sensitivity of the proposed predictor is reduced to 53%, but the specificity is increased to 91%, which corresponds to an average false positive rate of 0.8 event/day across the patient population. Conclusion: A ventricular tachyarrhythmia predictor based on a pattern of heart rate acceleration has been proposed that can yield sensitivity from 53% to 69%, with specificity up to 91%. Instances of this predictor increase significantly prior to an episode of tachyarrhythmia.

Abstract  Dicarboxylic acids in atmospheric aerosols have received much attention because of their potential roles in affecting the global climate. The composition and the sources of dicarboxylic acids in PM2.5 were studied at one remote and two urban sites in Hong Kong in the winter of 2000 and in the summer of 2001. Oxalate was the dominant dicarboxylic acid in all samples. The winter oxalate concentrations were high and spatially uniform, with an average value of 0.36 μg m−3, but the summer oxalate concentrations were low and had a large spatial variation. The influence of meteorological factors on the concentrations of dicarboxylic acids was also studied. The ratio of malonate to succinate was used to distinguish primary sources from secondary sources of these acids. This ratio at all three sites was close to that from direct vehicular exhaust in the winter, but it was close to that of secondary reactions in the summer. Hence, the acids were attributed to vehicular emissions in the winter and secondary sources in the summer. This hypothesis is also supported by a good correlation of oxalate with sulfate in the summer but a poor one in the winter. The correlations of oxalate with malonate, succinate, sulfate and K+ were also studied in terms of the routes of secondary formation of these dicarboxylic acids.

Abstract  An intensive sampling campaign was performed in Fresno, CA during December 2003 measuring fine particulate matter including both the semi-volatile and nonvolatile fractions of the aerosol. Both the newly developed R&P FDMS Monitor and a PC-BOSS have been shown to measure total PM2.5 concentrations including semi-volatile nitrate and organic material. Good agreement was observed between the PC-BOSS and the R&P FDMS Monitor in this study with linear regression analysis resulting in a zerointercept slope of 1.00 ± 0.02 and an R2 = 0.93. Several real-time measuring systems including the R&P Differential TEOM, the Met One BAMS, and a GRIMM Monitor were also employed and comparisons of total PM2.5 mass were made with the R&P FDMS Monitor. Agreement among these various monitors was generally good. However, differences were sometimes seen. Reasons for observed differences in the real-time mass measurement systems are explained by the composition and complexity of the measured aerosol, most importantly the composition of semi-volatile material. A newly automated ion chromatographic system developed by Dionex was also field tested and compared to both R&P 8400N Nitrate and integrated PC-BOSS inorganic species measurements. Sulfate and nitrate determined by the Dionex and PC-BOSS systems agreed. However, nitrate measured by the 8400N was low during fog events compared to the other two systems.

Abstract  For a period of almost 3 years, sampling of size-fractionated ambient particulate matter with diameter below 10 Ám (PM10) was performed at urban source sites (Downey and University of Southern California) and inland receptor sites (Claremont and Riverside) in the Los Angeles Basin as part of the Southern California Particle Center and Supersite. Results for size-resolved PM10 mass, inorganic ions (sulfate and nitrate), metals, elemental carbon, and organic carbon were obtained. Three collocated micro-orifice uniform deposit impactors (MOUDIs) were deployed to collect 24-hour samples roughly once a week. Ultrafine particle concentrations (particle diameter d p < 0.1 Ám) were found to be the highest at the source sites resulting from fresh vehicular emissions. Mass concentrations in the accumulation mode (0.1 < d p < 2.5 Ám) were lower in winter than in summer, especially at the receptor sites. PM concentrations in the coarse mode (2.5 < d p < 10 Ám) were lower in winter and were composed mostly of nitrate and crustal elements (iron, calcium, potassium, silicon, and aluminum). Consistent relative levels of these elements indicate a common source of soil and/or road dust. In the accumulation mode, nitrate and organic carbon were predominant with higher nitrate levels found at the receptor sites. The ultrafine mode PM consisted of mostly organic carbon, with higher wintertime levels at the source sites due to increased organic vapor condensation from vehicles at lower temperatures. Conversely, higher ultrafine organic carbon levels at the receptor areas are due to secondary organic aerosol formation by photochemical reactions as well as increased advection of polluted air masses from upwind.

Abstract  Measurements of NO and NO2 are reported using a highly modified photofragmentation two-photon laser-induced fluorescence (PF-TP-LIF) instrument. Available evidence suggests that the changes made substantially reduced wall decomposition of labile NOy species. In sharp contrast to the results reported from NASA's 1991 PEM-West A program where the median value for the ratio (NO2)(meas)/(NO2)(calc) was 3.36, the PEM-Tropics A observations produced a value for this ratio of 0.93. This represents the first time that remote upper tropospheric NO-NO2 data have shown a high degree of correspondence with current photochemical mechanisms.

Abstract  Background: Studies in monkeys with intranasally instilled gold ultrafine particles (UFPs; < 100 nm) and in rats with inhaled carbon UFPs suggested that solid UFPs deposited in the nose travel along the olfactory nerve to the olfactory bulb. Methods: To determine if olfactory translocation occurs for other solid metal UFPs and assess potential health effects, we exposed groups of rats to manganese (Mn) oxide UFPs (30 nm; ~ 500 μg/m3) with either both nostrils patent or the right nostril occluded. We analyzed Mn in lung, liver, olfactory bulb, and other brain regions, and we performed gene and protein analyses. Results: After 12 days of exposure with both nostrils patent, Mn concentrations in the olfactory bulb increased 3.5-fold, whereas lung Mn concentrations doubled; there were also increases in striatum, frontal cortex, and cerebellum. Lung lavage analysis showed no indications of lung inflammation, whereas increases in olfactory bulb tumor necrosis factor-α mRNA (~ 8-fold) and protein (~ 30-fold) were found after 11 days of exposure and, to a lesser degree, in other brain regions with increased Mn levels. Macrophage inflammatory protein-2, glial fibrillary acidic protein, and neuronal cell adhesion molecule mRNA were also increased in olfactory bulb. With the right nostril occluded for a 2-day exposure, Mn accumulated only in the left olfactory bulb. Solubilization of the Mn oxide UFPs was < 1.5% per day. Conclusions: We conclude that the olfactory neuronal pathway is efficient for translocating inhaled Mn oxide as solid UFPs to the central nervous system and that this can result in inflammatory changes. We suggest that despite differences between human and rodent olfactory systems, this pathway is relevant in humans.

Abstract  Global warming is predicted to be most pronounced at high latitudes, and observational evidence over the past 25 years suggests that this warming is already under way. One-third of the global soil carbon pool is stored in northern latitudes, so there is considerable interest in understanding how the carbon balance of northern ecosystems will respond to climate warming. Observations of controls over plant productivity in tundra and boreal ecosystems have been used to build a conceptual model of response to warming, where warmer soils and increased decomposition of plant litter increase nutrient availability, which, in turn, stimulates plant production and increases ecosystem carbon storage. Here we present the results of a long-term fertilization experiment in Alaskan tundra, in which increased nutrient availability caused a net ecosystem loss of almost 2,000 grams of carbon per square meter over 20 years. We found that annual aboveground plant production doubled during the experiment. Losses of carbon and nitrogen from deep soil layers, however, were substantial and more than offset the increased carbon and nitrogen storage in plant biomass and litter. Our study suggests that projected release of soil nutrients associated with high-latitude warming may further amplify carbon release from soils, causing a net loss of ecosystem carbon and a positive feedback to climate warming.

Abstract  Relatively high deposition of nitrogen (N) in the northeastern United States has caused concern because sites could become N saturated. In the past, mass-balance studies have been used to monitor the N status of sites and to investigate the impact of increased N deposition. Typically, these efforts have focused on dissolved inorganic forms of N (DIN = NH_4-N + NO_3-N) and have largely ignored dissolved organic nitrogen (DON) due to difficulties in its analysis. Recent advances in the measurement of total dissolved nitrogen (TDN) have facilitated measurement of DON as the residual of TDN - DIN. We calculated DON and DIN budgets using data on precipitation and streamwater chemistry collected from 9 forested watersheds at 4 sites in New England. TDN in precipitation was composed primarily of DIN. Net retention of TDN ranged from 62 to 89% (4.7 to 10 kg ha^minus 1 yr^minus 1) of annual inputs. DON made up the majority of TDN in stream exports, suggesting that inclusion of DON is critical to assessing N dynamics even in areas with large anthropogenic inputs of DIN. Despite the dominance of DON in streamwater, precipitation inputs of DON were approximately equal to outputs. DON concentrations in streamwater did not appear significantly influenced by seasonal biological controls, but did increase with discharge on some watersheds. Streamwater NO_3-N was the only fraction of N that exhibited a seasonal pattern, with concentrations increasing during the winter months and peaking during snowmelt runoff. Concentrations of NO_3-N varied considerably among watersheds and are related to DOC:DON ratios in streamwater. Annual DIN exports were negatively correlated with streamwater DOC:DON ratios, indicating that these ratios might be a useful index of N status of upland forests.

Abstract  As part of the Lake Champlain Basin watershed study of mercury (Hg) and pollutant deposition, cloud water and cloud throughfall collections were conducted at the south summit (1204 m) of Mt. Mansfield, Vermont between August 1 and October 31, 1998, for multi-element chemical analysis. A passive Teflon string collector was deployed during non-precipitating events to sample cloud/fog water at timberline, while three sets of paired funnels collected cloud throughfall under the red spruce-balsam fir canopy. Samples were analyzed for concentrations of Hg, major ions, and 10 trace elements. Ultra-clean sampling and analysis techniques were utilized throughout the study. Six events were sampled for cloud water alone and four events were sampled for both cloud water and cloud throughfall. Cloud throughfall chemistry showed substantial modification from incident cloud water. Much higher concentrations of Hg (2.3 x), base cations (Ca2+, K-, Mg2+; 3-18 x) and certain trace elements (Ni, Cu, Mn, Rb, Sr; 2-34 x) were observed in throughfall than in cloud water. These results confirm that cloud water can leach a wide variety of elements from tree foliage and wash off dry deposited elements. Cloud water deposited an average of 0.42 +/- 0.12 mm of water per hour. Estimated cloud water deposition of Hg was 7.4 microg m(-2) for the period August 1-October 31, approximately twice that deposited by rain during this period at a nearby low elevation Hg monitoring site. Our results indicate that cloud water and Hg deposition at Mt. Mansfield are likely to have considerable ecological effects.