Atmosphere2015, 6(8), 1032-1044; doi:10.3390/atmos6081032 - published 24 July 2015 Show/Hide Abstract
Abstract: Sensible heat flux (H) plays an important role in characterizations of land surface water and heat balance. There are various types of H measurement methods that depend on observation scale, from local-area-scale eddy covariance (EC) to regional-scale large aperture scintillometer (LAS) and remote sensing (RS) products. However, methods of converting one H scale to another to validate RS products are still open for question. A previous area-to-area regression kriging-based scaling method performed well in converting EC-scale H to LAS-scale H. However, the method does not consider the path-weighting function in the EC- to LAS-scale kriging with the regression residue, which inevitably brought about a bias estimation. In this study, a weighted area-to-area regression kriging (WATA RK) model is proposed to convert EC-scale H to LAS-scale H. It involves path-weighting functions of EC and LAS source areas in both regression and area kriging stages. Results show that WATA RK outperforms traditional methods in most cases, improving estimation accuracy. The method is considered to provide an efficient validation of RS H flux products.
Atmosphere2015, 6(8), 1006-1031; doi:10.3390/atmos6081006 - published 24 July 2015 Show/Hide Abstract
Abstract: The residents of Mexico City face serious problems of air pollution. Identifying the most representative scenarios for the transport and dispersion of air pollutants requires the knowledge of the main wind circulation patterns. In this paper, a simple method to recognize and characterize the wind circulation patterns in a given region is proposed and applied to the Mexico City winds (2001–2006). This method uses a lattice wind approach to model the local wind events at the meso-β scale, and hierarchical cluster analysis to recognize their agglomerations in their phase space. Data of the meteorological network of Mexico City was used as input for the lattice wind model. The Ward’s clustering algorithm with Euclidean distance was applied to organize the model wind events in seasonal clusters for each year of the period. Comparison of the hourly population trends of these clusters permitted the recognition and detailed description of seven circulation patterns. These patterns resemble the qualitative descriptions of the Mexico City wind circulation modes reported by other authors. Our method, however, permitted also their quantitative characterization in terms of the wind attributes of velocity, divergence and vorticity, and an estimation of their seasonal and annual occurrence probabilities, which never before were quantified.
Atmosphere2015, 6(8), 983-1005; doi:10.3390/atmos6080983 - published 24 July 2015 Show/Hide Abstract
Abstract: Topography is a significant factor influencing the spatial distribution of precipitation. This study developed a new methodology to evaluate and calibrate the Tropical Rainfall Measuring Mission Multi-satellite Precipitation Analysis (TMPA) products by merging geographic and topographic information. In the proposed method, firstly, the consistency rule was introduced to evaluate the fitness of satellite rainfall with measurements on the grids with and without ground gauges. Secondly, in order to improve the consistency rate of satellite rainfall, genetic programming was introduced to mine the relationship between the gauge rainfall and location, elevation and TMPA rainfall. The proof experiment and analysis for the mean annual satellite precipitation from 2001–2012, 3B43 (V7) of TMPA rainfall product, was carried out in eight mountainous areas of China. The result shows that the proposed method is significant and efficient both for the assessment and improvement of satellite precipitation. It is found that the satellite rainfall consistency rates in the gauged and ungauged grids are different in the study area. In addition, the mined correlation of location-elevation-TMPA rainfall can noticeably improve the satellite precipitation, both in the context of the new criterion of the consistency rate and the existing criteria such as Bias and RMSD. The proposed method is also efficient for correcting the monthly and mean monthly rainfall of 3B43 and 3B42RT.
Abstract: Due the rapid expansion of frac sand production, local residents, community leaders, and state regulatory authorities have expressed concerns regarding the lack of ambient respirable crystalline silica concentration data for areas near to these facilities. Long-term average data are needed to compare the fence line concentrations against chronic reference exposure guidelines such as the one adopted by the California Office of Environmental Health Hazard Assessment (OEHHA). This paper provides comprehensive sets of 24 h respirable crystalline silica concentration measurements compiled during multi-year sampling programs at the fence lines of four Wisconsin facilities—three frac sand mines and one frac sand processing plant. The authors adapted Environmental Protection Agency (EPA) reference method PM2.5 filter-based samplers to provide respirable (PM4) filter samples. Crystalline silica content of the PM4 particulate matter samples was measured using National Institute of Occupational Safety and Health (NIOSH) Method 7500 X-ray diffraction. The respirable crystalline silica limit of quantification was 0.31 µg/m3. The geometric mean (GM) respirable crystalline silica concentrations at the fence lines of the frac sand-producing facilities were less than 10% of the 3.0 µg/m3 California OEHHA chronic exposure level and were consistent with background concentrations throughout the upper Midwest of the U.S.
Abstract: Concentrations, size distributions and particle number vertical turbulent fluxes were measured by the eddy-covariance method at an urban background site in southeastern Italy during the summer. CO2/H2O concentrations and fluxes were also determined together with meteorological parameters. Time series show that particles could be divided into two size classes with negatively-correlated temporal trends in diurnal hours: nanoparticles (diameter Dp < 50 nm) and larger particles (Dp > 50 nm). Larger particles include part of the Aitken mode and the accumulation mode. Nanoparticles peaked in diurnal hours due to the presence of several days with nucleation events when particles Dp > 50 nm were at minimum concentrations. Nucleation increased diurnal total particle concentration by a factor of 2.5, reducing mean and median diameters from Dmean = 62.3 ± 1.2 nm and Dmedian = 29.1 ± 1.3 nm on non-event days to Dmean = 35.4 ± 0.6 nm and Dmedian = 15.5 ± 0.3 nm on event days. During nucleation events, particle deposition increased markedly (i.e., downward fluxes), but no significant changes in CO2 concentrations and fluxes were observed. This is compatible with new particle formation above the measurement height and a consequent net transport towards the surface. Correlation with meteorology shows that the formation of new particles is correlated with solar radiation and favored at high wind velocity.
Abstract: Ozone concentration has a complex distribution in mountain areas, but the low spatial density of high elevation monitoring stations has limited our understanding of ozone behavior. To achieve high spatial density, mobile measurement was carried out using a portable ozone monitor based on a semiconductor sensor. On the elevation gradient of a relatively low hill (273 m above seal level) in Matsuyama, Japan, 66 walking measurements were conducted in the pre-dawn hours of the winter in 2012 and 2013. The ozone concentration at the top of the hill was positively correlated with the daily maximum concentration on the plain on the previous day. The difference in ozone concentration between the top and bottom of the hill was found to increase with increasing vertical temperature difference. The measurement method established in this study provides a low-cost alternative to grasp the distribution of ozone in mountain areas.