Molecular Understanding of the Enhancement in Organic Aerosol Mass at High Relative Humidity.

The mechanistic pathway by which high relative humidity (RH) affects gas-particle partitioning remains poorly understood, although many studies report increased secondary organic aerosol (SOA) yields at high RH. Here, we use real-time, molecular measurements of both the gas and particle phase to provide a mechanistic understanding of the effect of RH on the partitioning of biogenic oxidized organic molecules (from α-pinene and isoprene) at low temperatures (243 and 263 K) at the CLOUD chamber at CERN. We observe increases in SOA mass of 45 and 85% with increasing RH from 10-20 to 60-80% at 243 and 263 K, respectively, and attribute it to the increased partitioning of semi-volatile compounds. At 263 K, we measure an increase of a factor 2-4 in the concentration of C10H16O2-3, while the particle-phase concentrations of low-volatility species, such as C10H16O6-8, remain almost constant. This results in a substantial shift in the chemical composition and volatility distribution toward less oxygenated and more volatile species at higher RH (e.g., at 263 K, O/C ratio = 0.55 and 0.40, at RH = 10 and 80%, respectively). By modeling particle growth using an aerosol growth model, which accounts for kinetic limitations, we can explain the enhancement in the semi-volatile fraction through the complementary effect of decreased compound activity and increased bulk-phase diffusivity. Our results highlight the importance of particle water content as a diluting agent and a plasticizer for organic aerosol growth.

Synergistic HNO3-H2SO4-NH3 upper tropospheric particle formation.

New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN)1-4. However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region5,6. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles-comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO3-H2SO4-NH3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.

Major lower extremity amputation in elderly patients with peripheral arterial disease: incidence and survival rates.

BACKGROUND AND AIMS: The methods of treating peripheral arterial disease (PAD) have changed and become more prophylactic. This study describes and analyzes 1) the incidence rates of major lower extremity amputation (LEA) due to PAD, 2) occurrence of re-amputation, and 3) the survival of amputees and factors predicting survival. METHODS: The series consisted of 210 patients (mean age 76.6, SD 10.7 yrs, 45.2% men) who underwent their first, i.e. index, major leg amputation because of PAD, in 1998-2002, in the city of Turku, Finland, population 175,000. RESULTS: The age-and gender-standardized incidence rate of combined above-knee and below-knee amputations was 24.1/100,000 person-years during 1998-2002. Thirty-four per cent of amputees underwent repetitive amputation. One-month mortality was 21% (n=45), one-year mortality 52% (n=109) and overall mortality 80% (n=168). Cardiovascular diseases predicted equally well 31-day, one-year, and overall mortality in age- and gender- adjusted analysis. Multiple co-morbidities (p=0.023) and unilateral above-knee amputations (p=0.047) were significant predictors for overall mortality in age- and gender-adjusted analysis. Cardiovascular diseases remained a significant predictor for 31-day and overall mortality in multivariate analysis (p=0.008 and p=0.015, respectively). Amputated patients' previous vascular procedures did not have any effect on mortality in the Cox model. Most revascularizations were performed less than six months before the index/first major LEA. CONCLUSION: Major LEAs seem to have been done late, and mainly for pain relief in the end-stage of patients with peripheral arterial disease.