ALBERT

Description: Iron-60 (60Fe) is a radioactive isotope in cosmic rays that serves as a clock to infer an upper limit on the time between nucleosynthesis and acceleration. We have used the ACE-CRIS instrument to collect 3.55 105 iron nuclei, with energies 195 to 500 megaelectron volts per nucleon, of which we identify 15 60Fe nuclei. The 60Fe56Fe source ratio is (7.5 2.9) 105. The detection of supernova-produced 60Fe in cosmic rays implies that the time required for acceleration and transport to Earth does not greatly exceed the 60Fe half-life of 2.6 million years and that the 60Fe source distance does not greatly exceed the distance cosmic rays can diffuse over this time, 1 kiloparsec. A natural place for 60Fe origin is in nearby clusters of massive stars.

Description: Air pollution in the Kathmandu valley is influenced by a variety of domestic and industrial sources such as garbage and biomass burning, brick kilns, and vehicular emissions. During non-monsoon seasons, the air quality index is considered hazardous, and consequently, air pollution is a leading cause of death in Nepal. During winter and spring of 2017-18, part two of the Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE-2) involved stationary sampling of gas and aerosol phase species in four locations across Nepal as well as 14 mobile measurement drives throughout the Kathmandu valley, Nepal. This work presents spatially and temporally resolved aerosol mass spectrometry and gas phase measurements from a mobile laboratory capable of high time resolution aerosol composition measurements. Spatially resolved aerosol composition results highlight chemical differences in aerosol due to strong regional sources, topography, and meteorology. For example, aerosol composition in regions with a high concentration of brick kilns had enhanced concentrations of sulfate aerosol, consistent with emission factors measured from brick kilns. Similarly, small towns outside of Kathmandu exhibited strongly elevated concentrations of chloride and organic aerosol due to garbage burning. These results are important for apportionment of the aerosol burden in the valley to their sources, and the consequent reduction of aerosol emissions.

Description: Air pollution is one of the most pressing environmental issues in the Kathmandu Valley, where the capital city of Nepal is located. We estimated emissions from two of the major source types in the valley (vehicles and brick kilns) and analyzed the corresponding impacts on regional air quality. First, we estimated the on-road vehicle emissions in the valley using the International Vehicle Emissions (IVE) model with local emissions factors and the latest available data for vehicle registration. We also identified the locations of the brick kilns in the Kathmandu Valley and developed an emissions inventory for these kilns using emissions factors measured during the Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) field campaign in April 2015. Our results indicate that the commonly used global emissions inventory, the Hemispheric Transport of Air Pollution (HTAP_v2.2), underestimates particulate matter emissions from vehicles in the Kathmandu Valley by a factor greater than 100. HTAP_v2.2 does not include the brick sector and we found that our sulfur dioxide (SO2) emissions estimates from brick kilns are comparable to 70 % of the total SO2 emissions considered in HTAP_v2.2. Next, we simulated air quality using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) for April 2015 based on three different emissions scenarios: HTAP only, HTAP with updated vehicle emissions, and HTAP with both updated vehicle and brick kilns emissions. Comparisons between simulated results and observations indicate that the model underestimates observed surface elemental carbon (EC) and SO2 concentrations under all emissions scenarios. However, our updated estimates of vehicle emissions significantly reduced model bias for EC, while updated emissions from brick kilns improved model performance in simulating SO2. These results highlight the importance of improving local emissions estimates for air quality modeling. We further find that model overestimation of surface wind leads to underestimated air pollutant concentrations in the Kathmandu Valley. Future work should focus on improving local emissions estimates for other major and underrepresented sources (e.g., crop residue burning and garbage burning) with a high spatial resolution, as well as the model's boundary-layer representation, to capture strong spatial gradients of air pollutant concentrations.

Description: Combustion of fuels in the residential sector for cooking and heating results in the emission of aerosol and aerosol precursors impacting air quality, human health, and climate. Residential emissions are dominated by the combustion of solid fuels. We use a global aerosol microphysics model to simulate the impact of residential fuel combustion on atmospheric aerosol for the year 2000. The model underestimates black carbon (BC) and organic carbon (OC) mass concentrations observed over Asia, Eastern Europe, and Africa, with better prediction when carbonaceous emissions from the residential sector are doubled. Observed seasonal variability of BC and OC concentrations are better simulated when residential emissions include a seasonal cycle. The largest contributions of residential emissions to annual surface mean particulate matter (PM2.5) concentrations are simulated for East Asia, South Asia, and Eastern Europe. We use a concentration response function to estimate the human health impact due to long-term exposure to ambient PM2.5 from residential emissions. We estimate global annual excess adult (〉  30 years of age) premature mortality (due to both cardiopulmonary disease and lung cancer) to be 308 000 (113 300–497 000, 5th to 95th percentile uncertainty range) for monthly varying residential emissions and 517 000 (192 000–827 000) when residential carbonaceous emissions are doubled. Mortality due to residential emissions is greatest in Asia, with China and India accounting for 50 % of simulated global excess mortality. Using an offline radiative transfer model we estimate that residential emissions exert a global annual mean direct radiative effect between −66 and +21 mW m−2, with sensitivity to the residential emission flux and the assumed ratio of BC, OC, and SO2 emissions. Residential emissions exert a global annual mean first aerosol indirect effect of between −52 and −16 mW m−2, which is sensitive to the assumed size distribution of carbonaceous emissions. Overall, our results demonstrate that reducing residential combustion emissions would have substantial benefits for human health through reductions in ambient PM2.5 concentrations.

Description: The Kathmandu Valley, an urban basin in Nepal, is subject to extreme air pollution events. Over 10% of Nepali fatalities are from lung disorders, making it the country's most common cause of mortality. The Nepal Ambient Monitoring and Source Testing Experiment [NAMaSTE-1] (2015) campaign establishes aerosol composition backgrounds and diurnal patterns at a suburban site east of Kathmandu. NAMaSTE-2 (2017-2018) builds upon this initial study with high time resolution aerosol and trace gas measurements at four air quality monitoring sites centered on the valley. Spatially resolved mobile AMS measurements taken across Kathmandu exhibit compositional differences due to topography and local sources. Aerosol composition near Kathmandu shows a distinct diurnal pattern, with extremely elevated concentrations overnight and into morning. This pattern is primarily driven by meteorology and strong afternoon westerly winds. Overnight the valley experiences weak easterly wind flows leading to increased concentrations of aerosols through confinement and stagnation from temperature inversions. Brick kilns, trash fires, as well as dung and biomass burning are ubiquitous regional primary emission sources; additional partitioning of secondary species such as ammonium, nitrate, and chlorides increase aerosol concentrations. Traffic remains a major source in Kathmandu; measurements at the Ratnapark urban site indicate, during peak traffic times, a four-fold increase in organic particles, a three-fold increase in chlorides, and large increases in NOx and black carbon. Relative contributions to aerosol composition at the different measurement sites will be discussed and provide integral information for mitigation efforts aimed at reducing exposure to ambient aerosols.