Nitric acid forming potential of five prototype hydrocarbons

The nitric acid formed from trans-2-butene, propene, ethene, toluene, and n-butane in single hydrocarbon/NO₂/purified air systems was examined in smog chamber experiments. The effect of hydrocarbon and NO₂ concentrations on the maximum HNO₃ yield, defined as percentages of initial NO₂ converted to HNO₃, was studied in two sets of experiments. In every hydrocarbon system, we found no effect of hydrocarbon concentration variation on the nitric acid formed. Out of initially added 100 ppb NO₂, in the hydrocarbon-rich systems, ethene formed most HNO₃ (45%), followed by propene, toluene, and n-butane (24%), and trans-2-butene (13%). When the initial NO₂ concentration was varied with a constant hydrocarbon concentration, the amount of HNO₃ formed was found to linearly increase with the added NO₂ down to |HC|/|NO₂| ratios, which depended on the nature of the hydrocarbon studied. The initial rate of HNO₃ formation in hydrocarbon excess experiments varied between 50, 35, 23, 16, and 8 ppb/hr for butene, propene, toluene, ethene, and butane systems, respectively.     

Assessment of the Relative Largest Earthquake Hazard Level in the NW Himalaya and its Adjacent Region

In the present study, the level of the largest earthquake hazard is assessed in 28 seismic zones of the NW Himalaya and its vicinity, which is a highly seismically active region of the world. Gumbel’s third asymptotic distribution (hereafter as GIII) is adopted for the evaluation of the largest earthquake magnitudes in these seismic zones. Instead of taking in account any type of M_max, in the present study we consider the ω value which is the largest earthquake magnitude that a region can experience according to the GIII statistics. A function of the form Θ(ω, RP_6.0) is providing in this way a relatively largest earthquake hazard scale defined by the letter K (K index). The return periods for the ω values (earthquake magnitudes) 6 or larger (RP_6.0) are also calculated. According to this index, the investigated seismic zones are classified into five groups and it is shown that seismic zones 3 (Quetta of Pakistan), 11 (Hindukush), 15 (northern Pamirs), and 23 (Kangra, Himachal Pradesh of India) correspond to a “very high” K index which is 6.     

Resolving the Effects of Aperture and Volume Restriction of the Flow by Semi-Porous Barriers Using Large-Eddy Simulations

The Regional Atmospheric Modelling System (RAMS)-based Forest Large-Eddy Simulation (RAFLES) model is used to simulate the effects of large rectangular prism-shaped semi-porous barriers of varying densities under neutrally buoyant conditions. RAFLES model resolves flows inside and above forested canopies and other semi-porous barriers, and it accounts for barrier-induced drag on the flow and surface flux exchange between the barrier and the air. Unlike most other models, RAFLES model also accounts for the barrier-induced volume and aperture restriction via a modified version of the cut-cell coordinate system. We explicitly tested the effects of the numerical representation of volume restriction, independent of the effects of the drag, by comparing drag-only simulations (where we prescribed neither volume nor aperture restrictions to the flow), restriction-only simulations (where we prescribed no drag), and control simulations where both drag and volume plus aperture restrictions were included. Previous modelling and empirical work have revealed the development of important areas of increased uplift upwind of forward-facing steps, and recirculation zones downwind of backward-facing steps. Our simulations show that representation of the effects of the volume and aperture restriction due to the presence of semi-porous barriers leads to differences in the strengths and locations of increased-updraft and recirculation zones, and the length and strength of impact and adjustment zones when compared to simulation solutions with a drag-only representation. These are mostly driven by differences to the momentum budget of the streamwise wind velocity by resolved turbulence and pressure gradient fields around the front and back edges of the barrier. We propose that volume plus aperture restriction is an important component of the flow system in semi-porous environments such as forests and cities and should be considered by large-eddy simulation (LES).