Kundan Lal Shrestha

High-resolution modeling and evaluation of ozone air quality of Osaka using MM5-CMAQ system

High-resolution modeling approach is increasingly being considered as a necessary step for improving the monitoring and predictions of regional air quality. This is especially true for highly urbanized region with complex terrain and land-use. This study uses Community Multiscale Air Quality (CMAQ) model coupled with MM5 mesoscale model for a comprehensive analysis to assess the suitability of such high-resolution modeling system in predicting ozone air quality in the complex terrains of Osaka, Japan. The 1-km and 3-km grid domains were nested inside a 9-km domain and the domain with 1-km grid covered the Osaka region. High-resolution Grid Point Value-Mesoscale Model (GPV-MSM) data were used after suitable validation. The simulated ozone concentrations were validated and evaluated using statistical metrics using performance criteria set for ozone. Daily maxima of ozone were found better simulated by the 1-km grid domain than the coarser 9-km and 3-km domains, with the maximum improvement in the mean absolute gross error about 3 ppbv. In addition, 1-km grid results fared better than other grids at most of the observation stations that showed noticeable differences in gross error as well as correlation. These results amply justify the use of the integrated high-resolution MMS-CMAQ modeling system in the highly urbanized region, such as the Osaka region, which has complex terrain and land-use.

Numerical Evaluation of the Impact of Urbanization on Summertime Precipitation in Osaka, Japan

This study utilized the Weather Research and Forecasting (WRF) model version 3.5.1 to evaluate the impact of urbanization on summertime precipitation in Osaka, Japan. The evaluation was conducted by comparing the WRF simulations with the present land use and no-urban land use (replacing “Urban” with “Paddy”) for August from 2006 to 2010. The urbanization increased mean air temperature by 2.1°C in urban areas because of increased sensible heat flux and decreased mean humidity by 0.8 g kg−1 because of decreased latent heat flux. In addition, the urbanization increased duration of the southwesterly sea breeze. The urbanization increased precipitation in urban areas and decreased in the surrounding areas. The mean precipitation in urban areas was increased by 20 mm month−1 (27% of the total amount without the synoptic-scale precipitation). The precipitation increase was generally due to the enhancement of the formation and development of convective clouds by the increase in sensible heat flux during afternoon and evening time periods. The urbanization in Osaka changes spatial and temporal distribution patterns of precipitation and evaporation, and consequently it substantially affects the water cycle in and around the urban areas of Osaka.

Impact of biogenic volatile organic compound emissions on ozone formation in the Kinki region, Japan

The standard Biogenic Volatile Organic Compound (BVOC) emissions from ten Japanese plant species were measured by using a growth chamber where temperature and light intensity can be controlled. These species were selected due to their abundance in the estimated domain of the Kinki region. The BVOC emissions in Kinki region during July 2002 were estimated by revising the standard BVOC emissions from temperature and light intensity which were calculated by MM5. The two types of the ozone calculation were carried out by CMAQ. One was the calculation with BVOC emissions (BIO). Another was the calculation that assumes BVOC emissions to be zero (NOBIO). The maximum ozone concentrations of BIO reasonably reproduced the observed maximum concentrations in especially the fine days. The hourly differences of monthly average ozone concentrations between BIO and NOBIO had the maximum value of 6ppb at 2 p.m. The explicit difference appeared in urban area, though the place where the maximum of difference occurred changed. It was shown that the BVOC emitted from the forest area strongly affected the ozone generation in the urban area.

High-resolution Air Quality Modelling And TimeScale Analysis Of Ozone And NOx In Osaka,Japan

The ozone pollution in the Osaka region is mainly influenced by the long-range transport of tropospheric ozone or its precursors from outside in winter but nearly 50% of the total ozone is chemically produced by regional emissions in summertime. The effects of the regional transport and the chemical production of ozone by regional emissions in summertime can be analysed by spectral decomposition of the time series and studying the inherent intra-day, diurnal and longer-term time scales in the time series of ozone and NOx. The relative contributions of these time scale components associated with different physical processes are also used to evaluate the performance of air quality models in simulating ozone and NOx. We used the Japanese national emission data with resolution of 10-km and 1-km resolution in the MM5-CMAQ modelling system for the nested simulation in Osaka with the finest domain having 1-km grid size. Among the different time scales, diurnal time scale has the highest correlation for ozone, and longer time scale has the highest correlation for NO and NO2. Spatial variation in the simulation of NOx is evident from the study of correlation of diurnal and longer-term time scales, with higher correlations in the longer-term time scale. Overall, the time scale analysis of ozone and NOx time series has proved useful for detailed quantitative analysis of the air quality modelling in Osaka.