Applications of Lagrangian dispersion modeling to the analysis of changes in the specific absorption of elemental carbon

International audienceWe use a Lagrangian dispersion model driven by a mesoscale model with four-dimensional data assimilation to simulate the dispersion of elemental carbon (EC) over a region encompassing Mexico City and its surroundings, the study domain for the 2006 MAX-MEX experiment, which was a component of the MILAGRO campaign. The results are used to identify periods when biomass burning was likely to have had a significant impact on the concentrations of elemental carbon at two sites, T1 and T2, downwind of the city, and when emissions from the Mexico City Metropolitan Area (MCMA) were likely to have been more important. They are also used to estimate the median ages of EC affecting the specific absorption of light, ?ABS, at 870 nm as well as to identify periods when the urban plume from the MCMA was likely to have been advected over T1 and T2. Median EC ages at T1 and T2 are substantially larger during the day than at night. Values of ?ABS at T1, the nearer of the two sites to Mexico City, were smaller at night and increased rapidly after mid-morning, peaking in the mid-afternoon. The behavior is attributed to the coating of aerosols with substances such as sulfate or organic carbon during daylight hours, but such coating appears to be limited or absent at night. Evidence for this is provided by scanning electron microscopy images of aerosols collected at the sampling sites. During daylight hours the values of ?ABS did not increase with aerosol age for median ages in the range of 1?4 h. There is some evidence for absorption increasing as aerosols were advected from T1 to T2 but the statistical significance of that result is not strong

Measured and modeled humidification factors of fresh smoke particles from biomass burning: role of inorganic constituents

During the 2006 FLAME study (<b>F</b>ire <b>L</b>aboratory <b>a</b>t <b>M</b>issoula <b>E</b>xperiment), laboratory burns of biomass fuels were performed to investigate the physico-chemical, optical, and hygroscopic properties of fresh biomass smoke. As part of the experiment, two nephelometers simultaneously measured dry and humidified light scattering coefficients (<i>b</i><sub>sp(dry) </sub> and <i>b</i><sub>sp(RH)</sub>, respectively) in order to explore the role of relative humidity (RH) on the optical properties of biomass smoke aerosols. Results from burns of several biomass fuels from the west and southeast United States showed large variability in the humidification factor (<i>f</i>(RH)=<i>b</i><sub>sp(RH)</sub>/<i>b</i><sub>sp(dry)</sub>). Values of <i>f</i>(RH) at RH=80–85% ranged from 0.99 to 1.81 depending on fuel type. We incorporated measured chemical composition and size distribution data to model the smoke hygroscopic growth to investigate the role of inorganic compounds on water uptake for these aerosols. By assuming only inorganic constituents were hygroscopic, we were able to model the water uptake within experimental uncertainty, suggesting that inorganic species were responsible for most of the hygroscopic growth. In addition, humidification factors at 80–85% RH increased for smoke with increasing inorganic salt to carbon ratios. Particle morphology as observed from scanning electron microscopy revealed that samples of hygroscopic particles contained soot chains either internally or externally mixed with inorganic potassium salts, while samples of weak to non-hygroscopic particles were dominated by soot and organic constituents. This study provides further understanding of the compounds responsible for water uptake by young biomass smoke, and is important for accurately assessing the role of smoke in climate change studies and visibility regulatory efforts

Mechanisms of Hematogenous Tumor Metastasis.

Metastasis is the most common cause of mortality associated with cancer, however, our understanding of these processes is insufficient. Metastasis is the end product of a dynamic process in which different interactions between cancer cells and the microenvironment of the organism result in the changes that allow these cells to exceed programmed behavior. Thus, cancer cells spread to new tissues and, ultimately, cause organ dysfunction and death. Understanding the molecular mechanisms involved in the process of metastasis may help to effectively and purposefully prevent and treat cancer metastasis. Attention of the modern researchers aimed at exploring ways to activate thrombosis, coagulation and formation of blood clots, as a prerequisite for metastasis of tumor cells. Sophisticated mechanisms of inducing and coagulation of platelets in combination with the increased activity of the activating vascular endothelial growth factor provide the onset of metastatic foci at a distance from the primary tumor. Learning and development opportunities to block these mechanisms is a promising way to improve the results of treatment of cancer patients. In this review article, we aimed to provide in a concise manner the prospects of studying mechanisms of tumor metastasis , as well as review existing today additional opportunities to optimize the results of treatment of cancer pathology

A qualitative comparison of secondary organic aerosol yields and composition from ozonolysis of monoterpenes at varying concentrations of NO₂

The effect of NO₂ on secondary organic aerosol (SOA) formation from ozonolysis of α-pinene, β-pinene, Δ³-carene, and limonene was investigated using a dark flow-through reaction chamber. SOA mass yields were calculated for each monoterpene from ozonolysis with varying NO₂ concentrations. Kinetics modeling of the first-generation gas-phase chemistry suggests that differences in observed aerosol yields for different NO₂ concentrations are consistent with NO₃ formation and subsequent competition between O₃ and NO₃ to oxidize each monoterpene. α-Pinene was the only monoterpene studied that showed a systematic decrease in both aerosol number concentration and mass concentration with increasing [NO₂]. β-Pinene and Δ³-carene produced fewer particles at higher [NO₂], but both retained moderate mass yields. Limonene exhibited both higher number concentrations and greater mass concentrations at higher [NO₂]. SOA from each experiment was collected and analyzed by HPLC-ESI-MS, enabling comparisons between product distributions for each system. In general, the systems influenced by NO₃ oxidation contained more high molecular weight products (MW > 400 amu), suggesting the importance of oligomerization mechanisms in NO₃-initiated SOA formation. α-Pinene, which showed anomalously low aerosol mass yields in the presence of NO₂, showed no increase in these oligomer peaks, suggesting that lack of oligomer formation is a likely cause of α-pinene's near 0 % yields with NO₃. Through direct comparisons of mixed-oxidant systems, this work suggests that NO₃ is likely to dominate nighttime oxidation pathways in most regions with both biogenic and anthropogenic influences. Therefore, accurately constraining SOA yields from NO₃ oxidation, which vary substantially with the volatile organic compound precursor, is essential in predicting nighttime aerosol production

K.: Correlations between optical, chemical and physical properties of biomass burn aerosols, Geophys

Abstract Aerosols generated from burning different plant fuels were characterized to determine relationships between chemical, optical and physical properties. Single scattering albedo (ω) and Angstrom absorption coefficients (α ap ) were measured using a photoacoustic technique combined with a reciprocal nephelometer. Carbon-to-oxygen atomic ratios, sp 2 hybridization, elemental composition and morphology of individual particles were measured using scanning transmission X-ray microscopy coupled with near-edge X-ray absorption fine structure spectroscop

Characterization of Aerosols Containing Zn, Pb, and Cl from an Industrial Region of Mexico City

Recent ice core measurements show lead concentrations increasing since 1970, suggesting new non automobile-related sources of Pb are becoming important worldwide (1). Developing a full understanding of the major sources of Pb and other metals is critical to controlling these emissions. During the March, 2006 MILAGRO campaign, single particle measurements in Mexico City revealed the frequent appearance of particles internally mixed with Zn, Pb, Cl, and P. Pb concentrations were as high as 1.14 μg/m3 in PM10 and 0.76 μg/m3 in PM2.5. Real time measurements were used to select time periods of interest to perform offline analysis to obtain detailed aerosol speciation. Many Zn-rich particles had needle-like structures and were found to be composed of ZnO and/or Zn(NO3)2·6H2O. The internally mixed Pb-Zn-Cl particles represented as much as 73% of the fine mode particles (by number) in the morning hours between 2-5 am. The Pb-Zn-Cl particles were primarily in the submicrometer size range and typically mixed with elemental carbon suggesting a combustion source. The unique single particle chemical associations measured in this study closely match signatures indicative of waste incineration. Our findings also show these industrial emissions play an important role in heterogeneous processing of NOy species. Primary emissions of metal and sodium chloride particles emitted by the same source underwent heterogeneous transformations into nitrate particles as soon as photochemical production of nitric acid began each day at ~7 am

Oil and gas impacts on air quality in federal lands in the Bakken region: an overview of the Bakken Air Quality Study and first results

The Bakken formation contains billions of barrels of oil and gas trapped in rock and shale. Horizontal drilling and hydraulic fracturing methods have allowed for extraction of these resources, leading to exponential growth of oil production in the region over the past decade. Along with this development has come an increase in associated emissions to the atmosphere. Concern about potential impacts of these emissions on federal lands in the region prompted the National Park Service to sponsor the Bakken Air Quality Study over two winters in 2013–2014. Here we provide an overview of the study and present some initial results aimed at better understanding the impact of local oil and gas emissions on regional air quality. Data from the study, along with long-term monitoring data, suggest that while power plants are still an important emissions source in the region, emissions from oil and gas activities are impacting ambient concentrations of nitrogen oxides and black carbon and may dominate recent observed trends in pollutant concentrations at some of the study sites. Measurements of volatile organic compounds also definitively show that oil and gas emissions were present in almost every air mass sampled over a period of more than 4 months

Microscopic Characterization of Carbonaceous Aerosol Particle Aging in the Outflow from Mexico City

This study was part of the Megacities Initiative: Local and Global Research Observations (MILAGRO) field campaign conducted in Mexico City Metropolitan Area during spring 2006. The physical and chemical transformations of particles aged in the outflow from Mexico City were investigated for the transport event of 22 March 2006. A detailed chemical analysis of individual particles was performed using a combination of complementary microscopy and micro-spectroscopy techniques. The applied techniques included scanning transmission X-ray microscopy (STXM) coupled with near edge X-ray absorption fine structure spectroscopy (NEXAFS) and computer controlled scanning electron microscopy with an energy dispersive X-ray analyzer (CCSEM/EDX). As the aerosol plume evolves from the city center, the organic mass per particle increases and the fraction of carbon-carbon double bonds (associated with elemental carbon) decreases. Organic functional groups enhanced with particle age include: carboxylic acids, alkyl groups, and oxygen bonded alkyl groups. At the city center (T0) the most prevalent aerosol type contained inorganic species (composed of sulfur, nitrogen, oxygen, and potassium) coated with organic material. At the T1 and T2 sites, located northeast of T0 (~;;29 km and ~;;65 km, respectively), the fraction of homogenously mixed organic particles increased in both size and number. These observations illustrate the evolution of the physical mixing state and organic bonding in individual particles in a photochemically active environment