Simulation of Some Air Pollutants and Weather Parameters Using WRF/Chem Model in Cairo and Qena Cities/ Egypt

Weather Research & Forecasting/ Chemistry model (WRF/Chem) has been used for simulat ion of air pollutants and weather parameters in Cairo (urban) and Qena (suburb) regions/ Egypt. Surface ozone (O3), Nitrogen oxides (NOx) and Nitrogen dioxide (NO2) as well as Wind speed (WS), Wind direction (WD) and Temperature (T) have been simulated in Cairo. While in Qena, only (O3), (WS), (WD) and (T) have been simulated. Different predict ion performance measures have been used to assess the accuracy of estimation of these parameters. The study showed that the model can simulate the diurnal variation of ozone in Cairo better than that in Qena, although the best quantitative estimates of ozone were found in Qena. The model failed in quantitative and qualitative estimation of NOx and NO2 in Cairo as these pollutants affected directly by traffic intensity. The model estimated the weather parameters in acceptable accuracy in both Cairo and Qena especially WS and T. It is clear that WRF/Chem model cannot generally simulate the chemical parameters in high polluted regions such as Cairo. This may be resulted from the coarse resolution used for the input meteorological and emission data (1 latitude X 1 longitude). While, it can be used safely in rural and suburban regions such as Qena. Using fine coarse resolution for meteorology and emission data may improve the results.


Introduction
Recently, concentration of gaseous, liquid and solid pollutants has been increased in the atmosphere as a result of urbanization and increasing of population [1,2,3]. This increase may be lead to undesired environmental and climatic effects. Consequently, the need for measuring these pollutants (such as NOx, NO 2 , O 3 and PM 10) as well as the meteorological parameters affecting its concentrations such as WS, WD and T has been increased. Unfortunately, measurement networks cannot be established in all the necessary locations, especially in the development countries. So that, the need for estimating these parameters by using some established models became necessary.
Weather research and forecasting (WRF/ Chem) model has been used in many studies for est imat ing and study ing meteorological and chemical parameters for instance [4,5,6]. It has been developed as a collaborative effort among several research institutes includ ing the NCA R Mesoscale and Microscale Meteo ro logy (MMM ) Div ision , the Nat ional The valley may affect the prevailing northerly wind by channeling it along the north south axis [8]. The meteorological situation of Cairo is largely determined by the vast surrounding desert; the west and the east deserts. Cairo city is highly populated; its inhabitances are more than 15 millions. About 52% of the industries and about 40% of electrical power stations in Egypt are found in Cairo. Consequently, it is considered as one of the most polluted mega cities in the world [9]. It characterized with narrow streets and high buildings, more than 1.5 million cars with the industrial regions represent the main sources of air pollution. In the other hand, Qena (26.20 o N & 32.75 o E) is a small city located about 600 Km south of Cairo. Its area is about 1,800 km², situated on the east bank of the Nile. Its climate is characterized by cold winter, and very hot but non-humid summe r.

Data and Methodology
In Cairo, data have been monitored by Egyptian Environmental Affairs Agency, Environmental Information and Monitoring Program EEAA-EIMP. We used O 3 values measured in El Abbassyia station. Instruments were located in a shelter on the top of 3 floors build ing. Air intake was 1 m fro m the Wall, about 16-m above the street level. The area was considered as regional residential area. It is normally up-wind fro m Cairo city center, but down-wind fro m the Shoubra industrial area and Shoubra urban area. There was no immed iate local sources, but regionally exposed. So, this station was considered as representative for regional urban area. O 3 was measured by UV-Photometric Absorption instrument model TEL M 49 C. Meteorological parameters were measured by Automatic Weather Station (AWS). NO 2 and NO x were measured by Chemilu minescence instrument model TEL M 42 C in Maadi, about 15 Km south of Abbassyia station. Instruments were located in the first floor of EEAA building, Intake about 4m fro m the ground. This area was polluted main ly by traffic and general act ivities of people.
In Qena, O 3 and meteorological parameters have been monitored in South valley university (SVU)-meteorological research station. O 3 measurements were carried out by the Model 49C UV Photometric Ozone Analy zer. The station is located about 6 KM northeast of Qena city in the eastern desert.

WRF/ Che m Configurati on
We used WRF/Chem model version 2.1 [10] for simu lation of the chemical and meteorological parameters in Cairo and Qena. Configuration of the model is illustrated in table 1.  Different prediction performance measures are used to assess the accuracy of estimation of these parameters including Mean Normalized Bias Error (M NBE) often just called the bias, Mean Absolute Normalized Gross Error (MANGE). It quantifies the mean absolute deviation of the residuals and indicates the average unsigned discrepancy between hourly estimates and observations. It is a robust measure o f overall model performance (http://www.tva.gov/ sami/ met/eval/ch5.pdf). The model efficiency (M E) is proposed as the best overall measure of agreement between observed and simu lated values. The following formu las are used for calcu lating these measures: Where, Y e : is the model estimated (modeled) value, Y m : is the measured value, N: is the number of observations.
Where, m Y : is the mean of the measured values.
In all the above statistical tests of accuracy, except M E, The smaller the value, the better the efficiency of the Model, while value of M E closer to 1 ind icates the superior model performance [13].   These findings agree with many studies that have been achieved for using WRF/chem model for simu lation air pollutants and weather parameters. For instance, the model represented the diurnal temperature cycle on the west of the Mexico City well, though surface temperatures were generally underestimated. Overall, the timing and amp litudes of the calculated diurnal variations of NOx, and O3 ag reed well with measurements, especially for O3 [14]. Also, the WRF/Chem model statistically showed better skill in forecasting O 3 than MM5/chem model with no appreciable d ifferences between models in terms of b ias with the observations. Also, the WRF/Chem model consistently exhibited better skill at forecasting the O 3 precursors CO and NOy at all of the surface sites. However, the W RF/ Chem model b iases of these precursors and other gas-phase species were persistently higher than for MM5/ Chem, and were most often biased high compared to observations [15]. Also, the comparison between simulated and observed temperature and wind fields showed that the Weather Research and Forecasting Model succeeded in generation of meteorological inputs required for AERMOD model in Pune, India [16].  It is found that WRF/Chem model can simu late diurnal variation of O 3 values in Cairo better than that in Qena, although, the quantitative estimation in Qena is better than that in Cairo. Simu lation of NO x and NO 2 in Cairo was not good neither quantitative nor qualitative. Th is may be resulted fro m the coarse resolution used for the input meteorological and emission data (1 o lat itude X 1 o Longitude) as well as the fact that these pollutants affected directly by local emissions. The model simulated the weather parameters in acceptable accuracy in both Cairo and Qena especially WS and T. It is clear that WRF/Chem model can not generally simu late the chemical parameters in high polluted regions. While, it can be used safely in rural and suburban regions. Using fine resolution for meteorology and emission data can improve the results. WRF/ Chem model can be used in Egypt for estimation weather and chemical parameters required for pollutant sources and sinks study. Where, in most of the Egyptian Cities there are shortage in direct measurements of these parameters.