Impacts of Combustion Conditions and Photochemical Processing on the Light Absorption of Biomass Combustion Aerosol.

The aim was to identify relationships between combustion conditions, particle characteristics, and optical properties of fresh and photochemically processed emissions from biomass combustion. The combustion conditions included nominal and high burn rate operation and individual combustion phases from a conventional wood stove. Low temperature pyrolysis upon fuel addition resulted in "tar-ball" type particles dominated by organic aerosol with an absorption Ångström exponent (AAE) of 2.5-2.7 and estimated Brown Carbon contributions of 50-70% to absorption at the climate relevant aethalometer-wavelength (520 nm). High temperature combustion during the intermediate (flaming) phase was dominated by soot agglomerates with AAE 1.0-1.2 and 85-100% of absorption at 520 nm attributed to Black Carbon. Intense photochemical processing of high burn rate flaming combustion emissions in an oxidation flow reactor led to strong formation of Secondary Organic Aerosol, with no or weak absorption. PM1 mass emission factors (mg/kg) of fresh emissions were about an order of magnitude higher for low temperature pyrolysis compared to high temperature combustion. However, emission factors describing the absorption cross section emitted per kg of fuel consumed (m(2)/kg) were of similar magnitude at 520 nm for the diverse combustion conditions investigated in this study. These results provide a link between biomass combustion conditions, emitted particle types, and their optical properties in fresh and processed plumes which can be of value for source apportionment and balanced mitigation of biomass combustion emissions from a climate and health perspective.

Particulate PAH emissions from residential biomass combustion: time-resolved analysis with aerosol mass spectrometry.

Time-resolved emissions of particulate polycyclic aromatic hydrocarbons (PAHs) and total organic particulate matter (OA) from a wood log stove and an adjusted pellet stove were investigated with high-resolution time-of-flight aerosol mass spectrometry (AMS). The highest OA emissions were found during the addition of log wood on glowing embers, that is, slow burning pyrolysis conditions. These emissions contained about 1% PAHs (of OA). The highest PAH emissions were found during fast burning under hot air starved combustion conditions, in both stoves. In the latter case, PAHs contributed up to 40% of OA, likely due to thermal degradation of other condensable species. The distribution of PAHs was also shifted toward larger molecules in these emissions. AMS signals attributed to PAHs were found at molecular weights up to 600 Da. The vacuum aerodynamic size distribution was found to be bimodal with a smaller mode (Dva ∼ 200 nm) dominating under hot air starved combustion and a larger sized mode dominating under slow burning pyrolysis (Dva ∼ 600 nm). Simultaneous reduction of PAHs, OA and total particulate matter from residential biomass combustion may prove to be a challenge for environmental legislation efforts as these classes of emissions are elevated at different combustion conditions.

Impact on short-lived climate forcers increases projected warming due to deforestation.

The climate impact of deforestation depends on the relative strength of several biogeochemical and biogeophysical effects. In addition to affecting the exchange of carbon dioxide (CO2) and moisture with the atmosphere and surface albedo, vegetation emits biogenic volatile organic compounds (BVOCs) that alter the formation of short-lived climate forcers (SLCFs), which include aerosol, ozone and methane. Here we show that a scenario of complete global deforestation results in a net positive radiative forcing (RF; 0.12 W m-2) from SLCFs, with the negative RF from decreases in ozone and methane concentrations partially offsetting the positive aerosol RF. Combining RFs due to CO2, surface albedo and SLCFs suggests that global deforestation could cause 0.8 K warming after 100 years, with SLCFs contributing 8% of the effect. However, deforestation as projected by the RCP8.5 scenario leads to zero net RF from SLCF, primarily due to nonlinearities in the aerosol indirect effect.

Novel insights on new particle formation derived from a pan-european observing system.

The formation of new atmospheric particles involves an initial step forming stable clusters less than a nanometre in size (<~1 nm), followed by growth into quasi-stable aerosol particles a few nanometres (~1-10 nm) and larger (>~10 nm). Although at times, the same species can be responsible for both processes, it is thought that more generally each step comprises differing chemical contributors. Here, we present a novel analysis of measurements from a unique multi-station ground-based observing system which reveals new insights into continental-scale patterns associated with new particle formation. Statistical cluster analysis of this unique 2-year multi-station dataset comprising size distribution and chemical composition reveals that across Europe, there are different major seasonal trends depending on geographical location, concomitant with diversity in nucleating species while it seems that the growth phase is dominated by organic aerosol formation. The diversity and seasonality of these events requires an advanced observing system to elucidate the key processes and species driving particle formation, along with detecting continental scale changes in aerosol formation into the future.

Diesel soot aging in urban plumes within hours under cold dark and humid conditions.

Fresh and aged diesel soot particles have different impacts on climate and human health. While fresh diesel soot particles are highly aspherical and non-hygroscopic, aged particles are spherical and hygroscopic. Aging and its effect on water uptake also controls the dispersion of diesel soot in the atmosphere. Understanding the timescales on which diesel soot ages in the atmosphere is thus important, yet knowledge thereof is lacking. We show that under cold, dark and humid conditions the atmospheric transformation from fresh to aged soot occurs on a timescale of less than five hours. Under dry conditions in the laboratory, diesel soot transformation is much less efficient. While photochemistry drives soot aging, our data show it is not always a limiting factor. Field observations together with aerosol process model simulations show that the rapid ambient diesel soot aging in urban plumes is caused by coupled ammonium nitrate formation and water uptake.

Use of isografts to study proliferation and differentiation programs of mouse stomach epithelia.

A new model system has been developed for studying the factors that regulate the proliferation and differentiation programs of the principal cell lineages present in the mouse stomach epithelium. When embryonic day 14 (E14) stomachs from C57Bl/6 mice are implanted under the subcutaneous fascia of young adult male CBY/B6 nude mouse recipients, they are rapidly vascularized and begin to grow at rates comparable to the intact stomach of a similarly aged animal. Single- and multilabel immunohistochemical studies, conducted in the intact stomach of E14 to postnatal day 42 (P42) C57Bl/6 mice and in P7, P14, P28, and P42 C57Bl/6 isografts, suggest that the apparently undifferentiated glandular epithelium of E14 stomach already has encoded positional information that permits it to establish regional differences in cell populations even in the absence of exposure to normal luminal contents. Regional differentiation is manifested by the establishment of distinct zones, each composed of gastric units with zone-specific cell lineages. This axial patterning evolves at a rate similar to that of the intact stomach, even though the E14 isograft is placed in the hormonal environment of an adult host and therefore cannot be programmed by normal developmental changes in endocrine status. Moreover, patterning is maintained in isografts despite continuous renewal of its epithelial cell lineages. Although isografts apparently possess autonomously functioning temporal and spatial programs, perturbations were noted in the proliferation and/or differentiation programs of certain lineages, e.g., the rate of accumulation of endocrine cell subpopulations is reduced in these grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel goblet cell gene related to IgGFcgammaBP is regulated in adapting gut after small bowel resection.

The loss of functional small bowel surface area leads to a well-described adaptive response in the remnant intestine. To elucidate its molecular regulation, a cohort of cDNAs were cloned using a rat gut resection model and subtractive/differential hybridization cloning techniques. This study reports a novel cDNA termed "ileal remnant repressed" (IRR)-219, which shares 80% nucleotide identity with the 3'end of a human intestinal IgG Fc binding protein (IgGFcgammaBP) and is homologous to human and rat mucins. IRR-219 mRNA is expressed in intestine and colon only. At 48 h after 70% intestinal resection, mRNA levels decreased two- to fivefold in the adaptive small bowel but increased two- to threefold in the colon. Expression of IRR-219 was suppressed in adaptive small bowel as late as 1 wk after resection. IRR-219 expression is also regulated during gut ontogeny. In situ hybridization revealed IRR-219 expression in small intestinal and colonic goblet cells only. Its unique patterns of expression during ontogeny and after small bowel resection suggest distinctive roles in small bowel and colonic adaptation.

Regulation of PC4/TIS7 expression in adapting remnant intestine after resection.

The adaptive response of the small intestine to loss of functional surface area includes enhanced crypt cell proliferation and enterocyte differentiation. To better define the underlying molecular and cellular mechanisms, we have cloned rat genes that are specifically regulated in the adaptive gut after 70% small intestinal resection. One of these is the immediate early gene PC4/TIS7. Compared with sham-resected control ileum, PC4/TIS7 mRNA levels in the adaptive remnant ileum were markedly increased at 16 and 48 h but not 1 wk after resection. Greater augmentation of PC4/TIS7 mRNA levels occurred in the ileum compared with the duodenum and proximal jejunum. After resection, the changes in intestinal PC4/TIS7 mRNA levels also exceeded changes in extraintestinal levels. The demonstration by in situ hybridization that villus-associated, but not crypt, cells express PC4/TIS7 mRNA is consistent with a role in regulating cytodifferentiation. The pattern of expression in the Caco-2 cell line is also consistent with such a role. Although the precise function of PC4/TIS7 in adaptation remains unclear, the early and intestine-specific changes in mRNA levels after 70% resection suggest that it might augment the adaptive response by stimulating the production of differentiated enterocytes.

Use of fetal intestinal isografts from normal and transgenic mice to study the programming of positional information along the duodenal-to-colonic axis.

The four principal cellular constituents of the mouse intestinal epithelium are all derived from a multipotent stem cell functionally anchored near the base of its crypts. Differentiation of enterocytes, enteroendocrine, and goblet cells occurs during an orderly upward migration from monoclonal crypts supplied by a single active stem cell to adjacent polyclonal small intestinal villi or to their colonic homologs, the surface epithelial cuffs. Paneth cells differentiate as they descend to the base of crypts. This epithelium undergoes rapid and perpetual renewal yet is able to maintain cephalocaudal (duodenal-to-colonic) differences in the differentiation programs of its four cell types from the time of its initial cytodifferentiation in late fetal life (embryonic (E) days 16-17). Rat liver fatty acid-binding protein/human growth hormone transgenes (Fabpl/hGH) have been used as novel phenotypic markers to describe the biological properties of gut stem cells and the differentiation programs of their enterocytic and enteroendocrine lineages. To determine whether the multipotent stem cell is able to retain a "positional" address in the absence of luminal signals, we prepared isografts from the proximal small intestine or distal small intestine and colon of E15-E16 Fabpl/hGH transgenic mice and their normal littermates and implanted them into the subcutaneous tissues of young, adult male CBY/B6 nude mice. Immunocytochemical and histochemical studies indicate that appropriate position-specific differences in the differentiation programs of each of the four principal cell lineages are present along the cephalocaudal and crypt-to-villus (or crypt-to-epithelial cuff) axes of isografts harvested 4-6 weeks after implantation. This suggests that the gut stem cell can be characterized not only by its multipotency and enormous capacity for self-renewal but also by its ability to be programmed (? imprinted) with positional information. Transgene expression is reduced in a number of enteroendocrine subpopulations in small intestinal and colonic isografts compared to the intact gut. Moreover, the decision to express the Fabpl/hGH transgene appears to be coordinated between adjacent crypts as evidenced by (i) the presence of multicrypt patches of wholly reporter (hGH)-positive or reporter-negative cells in the intact colon and in colonic isografts and (ii) by the presence of coherent bands of reporter-positive or -negative cells that emanate from adjacent monophenotypic crypts and extend to the apical extrusion zone of distal small intestinal villi.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of rat epimorphin/syntaxin 2 expression suggests a role in crypt-villus morphogenesis.

The rodent intestinal mucosa undergoes a remarkable morphogenesis as the crypt-villus axis is formed. Endoderm-mesenchymal interactions play a critical role in this process. Epimorphin is a mesenchymal protein postulated to play a role in lung and skin morphogenesis. The rat homologue, syntaxin 2, belongs to a family of integral membrane proteins that function in vesicle docking and fusion. To clarify its role in fetal gut morphogenesis, epimorphin expression was examined during ontogeny, in an isograft model of ischemic injury and mucosal repair, and during intestinal adaptation after small bowel resection. Epimorphin/syntaxin 2 mRNA levels were increased in fetal gut during lumen formation and villus morphogenesis. mRNA levels remained elevated in the first 2 wk after birth and then declined at weaning. In situ hybridization showed epimorphin/syntaxin 2 mRNA in gestational day 14 (G14) and G15 intestinal mesenchymal cells and in the mucosal lamina propria during villus formation. Epimorphin/syntaxin 2 mRNA expression increased during villus repair in the isograft. In contrast, in the early stages of intestinal adaptation after small bowel resection, epimorphin/syntaxin 2 mRNA expression was suppressed in the adapting gut. We conclude the cell-specific and temporal patterns of epimorphin expression in the models used in this study suggest a role in the morphogenesis of the crypt-villus axis.

Analysis of cloned cDNAs differentially expressed in adapting remnant small intestine after partial resection.

After partial resection, the remnant small intestine undergoes an adaptive response. Little is known about the molecular and cellular basis of intestinal adaptation. To identify genes transcriptionally regulated in response to loss of functional bowel surface area, we have isolated cDNAs differentially expressed in the adaptive ileum 48 h after 70% proximal small intestinal resection. A cDNA library constructed from the remnant ileum of rats subjected to resection was screened using subtractive hybridization techniques. Several groups of cDNA clones that were induced during intestinal adaptation were isolated. The first included liver fatty acid binding protein, apolipoprotein A-IV, cellular retinol binding protein II, and ileal lipid binding protein. These all encode proteins involved in the absorption, metabolism, and trafficking of nutrients. A second group included the catalytic subunit of protein phosphatase 1 delta, a 78-kDa glucose-regulated protein (grp 78; a glucose-regulated member of the 70-kDa heat-shock protein family), and several pancreatitis-associated proteins. A third group of induced genes contained novel cDNAs. To better characterize the adaptive response, the temporal, spatial, and cellular patterns of expression of several of these genes were analyzed with the use of immunohistochemical and in situ hybridization techniques. These studies indicate that during early adaptation, genes involved in nutrient trafficking, protein processing, and cell cycle regulation are transcriptionally regulated in the residual small intestine in distinct temporal and regional patterns consistent with a complex multifaceted response to intestinal resection.

Enterocytic gene expression in intestinal adaptation: evidence for a specific cellular response.

After massive small bowel resection, the remnant gut epithelium undergoes an adaptive response marked by an increase in villus height, crypt depth, and crypt cell production rate. Although morphological features of gut adaptation have been well characterized, the differentiation status and response of epithelial cells populating the adaptive villus is unclear. To address these issues, cell-specific and spatial patterns of expression of a set of enterocytic genes were characterized in rats after 70% small bowel resection. The liver and intestinal (I) fatty acid binding protein (FABP) and apolipoprotein A-I (apo A-I) and apo A-IV genes were studied because they exhibit unique regional and cell-specific patterns of expression in the developing and adult gut. At 48 h after surgery, apo A-IV and I-FABP mRNA levels were increased up to 3.5-fold in adaptive remnant ileum compared with sham-operated or sham-resected control ileum. In situ hybridization and immunohistochemical analyses revealed a marked increase in enterocytic apo A-IV mRNA and protein expression in the adaptive ileum, from villus base to tip but not in crypts. By 1 wk after resection, apo A-IV, but not I-FABP, mRNA levels remained elevated in remnant ileum, although duodenal I-FABP mRNA levels were still increased. In contrast, apo A-I mRNA levels were not significantly induced. These results indicate that the enterocyte can respond acutely to loss of small bowel surface area by increasing expression of several genes. This compensatory enterocytic response is spatially (from duodenum to ileum) and temporally regulated. These results suggest initiation of the adaptive response occurs by way of a complex set of molecular pathways involving villus and crypt cells.