In virtually all published literature wherein closure between gravimetric and chemical measurements is tested, the concentration of particulate organics is estimated by multiplying the measured concentration of organic carbon (micrograms carbon/cubic meter air) by a factor of 1.2 -1.4. This factor, which is an estimate of the average molecular weight per carbon weight for the organic aerosol, stems from very limited theoretical and laboratory studies conducted during the 1970s. This investigation suggests that 1.4 is the lowest reasonable estimate for the organic molecular weight per carbon weight for an urban aerosol and that 1.4 does not accurately represent the average organic molecular weight per carbon weight for a nonurban aerosol. Based on the current evaluation, ratios of 1.6 § 0.2 for urban aerosols and 2.1 § 0.2 for nonurban aerosols appear to be more accurate. Measurements are recommended. Literature values also suggest that 1.2 g/cm 3 is a reasonable estimate for the organic aerosol density. This quantity is needed to convert between geometric and aerodynamic size distributions (e.g., to predict aerosol optical properties and understand cloud nucleating properties).

In virtually all published literature wherein closure between gravimetric and chemical measurements is tested, the concentration of particulate organics is estimated by multiplying the measured concentration of organic carbon (micrograms carbon/cubic meter air) by a factor of 1.2 -1.4. This factor, which is an estimate of the average molecular weight per carbon weight for the organic aerosol, stems from very limited theoretical and laboratory studies conducted during the 1970s. This investigation suggests that 1.4 is the lowest reasonable estimate for the organic molecular weight per carbon weight for an urban aerosol and that 1.4 does not accurately represent the average organic molecular weight per carbon weight for a nonurban aerosol. Based on the current evaluation, ratios of 1.6 § 0.2 for urban aerosols and 2.1 § 0.2 for nonurban aerosols appear to be more accurate. Measurements are recommended. Literature values also suggest that 1.2 g/cm 3 is a reasonable estimate for the organic aerosol density. This quantity is needed to convert between geometric and aerodynamic size distributions (e.g., to predict aerosol optical properties and understand cloud nucleating properties).

Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive experimentation, homogeneous formation of secondary organic aerosol (SOA) from isoprene remains unproven. Herein, an incloud process is identified in which isoprene produces SOA. Interstitial oxidation of isoprene produces water-soluble aldehydes that react in cloud droplets to form organic acids. Upon cloud evaporation new organic particulate matter is formed. Cloud processing of isoprene contributes at least 1.6 Tg yr(-1) to a global biogenic SOA production of 8-40 Tg yr(-1). We conclude that cloud processing of isoprene is an important contributor to SOA production, altering the global distribution of hygroscopic organic aerosol and cloud condensation nuclei.

We provide detailed mechanisms of Ahnak-mediated potentiation of transforming growth factor β (TGFβ) signaling, which leads to a negative regulation of cell growth. We show that Smad3 interacts with Ahnak through MH2 domain and that Ahnak stimulates Smad3 localization into nucleus leading to potentiating TGFβ-induced transcriptional activity of R-Smad. Moreover, overexpression of Ahnak resulted in growth retardation and cell cycle arrest through downregulation of c-Myc and cyclin D1/D2. We describe results from analyses of Ahnak−/− mouse model expressing middle T antigen in a mammary gland-specific manner (MMTVTg/+Ahnak−/−), which showed significantly progressed hyperplasia of mammary glands compared with MMTVTg/+Ahnak+/+. Finally, we screened multiple human breast cancer tissues and showed that the expression of Ahnak in cancer tissues is lower than that in control tissues by 50%. Taken together, these data indicate that Ahnak mediates a negative regulation of cell growth and acts as novel tumor suppressor through potentiation of TGFβ signaling.

During the Pittsburgh Air Quality Study (PAQS) an automated semi-continuous thermal-optical transmittance (TOT) carbon analyzer was used to measure 2-4 h average particulate organic (OC) and elemental carbon (EC) concentrations from July 1, 2001 to August 13, 2002. To minimize the adsorption of vapor-phase organics, the sample air was drawn through a multi-channel parallelplate diffusion denuder placed upstream of the carbon analyzer. Particulate OC and EC in the sample air were then collected on a quartz fiber filter (QFF) mounted inside the carbon analyzer, and analyzed immediately after collection. To account for any remaining organic vapors not retained by the denuder and collected on the sampling filter (positive artifact) a dynamic blank was run every two weeks. An upper-bound estimate of volatilization induced by the presence of the denuder upstream of the sampling filter (negative artifact) was also made. A detailed description of the operating protocol and quality assurance measurements is provided. The contributions of primary and secondary organic aerosol (SOA) to particulate OC were calculated using an "EC tracer method," which is 1995). Examination of concentration dynamics suggests that multi-day formation and regional transport is an important contributor to the higher SOA contributions to OC in Pittsburgh and suggests that SOA is likely to be a particularly important contributor to particulate OC in locations that are recipients of long distance transport, such as the eastern United States.