Detection of Increasing of Tropospheric NO 2 over some Iraqi Cities by using Satellite Data

This paper focus on study the variations of monthly tropospheric NO2 concentrations over three Iraqi cities Baghdad (33.3° N, 44.4° E), Basrah (30.56° N, 47.8° E) and Erbil (36.3° N, 44.06° E). Monthly NO2 retrievals from the Ozone Monitoring Instrument (OMI) onboard Aura satellite during the period from October 2004 to March 2013 have been used. The results show a high monthly and annual NO2 concentrations at Baghdad than Basra and Erbil may be attribute to high densely populations and a high economic activity. During the whole period, Baghdad, Basrah and Erbil were exhibited an average of NO2 (8.1±2.5), (3.7±1.3) and (3.3±1.7) in unit 10 15 molecules/cm 2 respectively. The maximum concentration of NO2 is found in winter season in all year due to enhancement of atmospheric photochemistry. An elevated trend of NO2 concentration is found in study sites where maximum annual increase in NO2 is found at Erbil (11.53 % per year), Basrah (8.59 % per year) and Baghdad (7.42 % per year). A statistical study is needed to evaluate the economic activity in Iraqi cities to understand the reason of growing the air pollution over Iraqi cities.


Introduction
Environmental pollution is an important subject because of its relationship to climate change, in addition to serious health effects on human.Nitrogen oxides (NOx= NO + NO 2 ) is one of significant segments of air pollution and play a vital role in chemistry of the atmosphere.The main NOx in the troposphere is nitric oxide (NO) and nitrogen dioxide (NO 2 ) and collectively combined as nitrogen oxides [1].The key source of NO 2 producing from human activities is the combustion of fossil fuels (coal, gas and oil).In cities, about 80% of surrounding NO 2 results from motor vehicles.Some other sources include refining of gasoline and metals, commercial and food processing; generation of electricity power using fossil fuels also produces significant portions of this gas [2].The contribution of fossil fuel combustion is regarding around 2/3 of the global source of NOx [1] and is concentrated in urban areas.Nitrogen oxides are important for the distribution of ozone (O3) and hydroxyl (OH) in the atmosphere.The role of nitrogen oxides in the troposphere varies from the role of nitrogen oxides in the stratosphere.Nitrogen oxides in the troposphere lead to ozone production, while in the stratosphere it assumes a part in the destruction of ozone.Several of satellite sensors measured the global tropospheric NO 2 distributions such as: Global Ozone Monitoring Experiment (GOME) at period (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) aboard ERS-2, Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) (from 2002) aboard Envisat platform and Ozone Monitoring Instrument (OMI) aboard EOS-AURA (from 2004) [3, 4, 5& 6].This study is focus on the tropospheric NO 2 concentration measured by the satellite instrument (OMI).OMI is a space borne spectroradiometer measures in three broad spectral regions (UV-1, UV-2, and VIS) with a spectral resolution of 0.5 nm.Of trace gases that can be recovered from OMI,

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Ozone and NO 2 are identified as fundamental measurements, both for monitoring of the stratospheric ozone layer and for tropospheric air quality [7].The global coverage and the pixel size of 24×13 km 2 make OMI is well suited to observe sources of air pollution.It has recently been shown that satellite observations of tropospheric nitrogen dioxide are useful in estimating anthropogenic emissions of nitrogen oxides [8, 9, 10, 11& 12], in observing emissions by soils [13] and in putting constraints on NOx production by lightning [14,15,16].[17] observed a significant increase in nitrogen oxides emissions due to the rising in industry activity and traffic.In rearmost years Iraq start growing in economic activity by increase of industry activity and traffic which led to increased emissions of tropospheric pollutants.Through monitoring satellite images, high concentrations of NO 2 emissions are found on densely populated and industrialized cities centers in Iraq, as illustrated by the Figure 1.This research focus on monthly concentration of NO 2 obtained from OMI to investigate monthly, seasonal, annual variations and annual increase of NO 2 over three Iraqi cities during the period from October 2004 to March 2013.Satellite observations of NO 2 are based on optical absorption spectroscopy principle to scattered sunlight.The NO 2 molecule has strong and structured absorption bands in the ultraviolet and visible spectral range which makes it typical target gas for retrievals using the Differential Optical Absorption Spectroscopy (DOAS).To transform atmospheric NO 2 column to tropospheric NO 2 column, the stratospheric component has to be extracted and the sensitivity of the measurement with altitude has to be taken into account [19].Through the period there is an increasing of NO 2 concentration was observed in three major Iraqi cities.This may be due to enhanced production resulting from increased number of motor vehicles, electric power generators, industrial activities which are used fossil fuels.From the observations, it is show that NO 2 concentrations suffer an increasing tendency during the study period.The annual increase of NO 2 concentrations is shown in Table (1).
The present study uses DOMINO (Derivation of OMI tropospheric NO 2 , version 2) products which provide from Tropospheric Emission Monitoring Internet Service.This paper deal with analysis of the spatial-temporal structure of NO 2 retrieved from OMI sensor over cities in the northern, central and southern region of the Iraq: Erbil (36.313°N, 44.062° E), Baghdad (33.313°N, 44.437° E) and Basrah (30.563 ° N, 47.812° E) respectively.Monthly average concentrations of the NO2 data were used for an examination of the monthly, seasonal and annual variations during the period from October 2004 to March 2013 and calculate the percentage of annual increase (I %) of the NO2 columns over three Iraqi cities by using the equation: I %=( c2-c 1 )/c1*100 ………………………..(1) where c 1 is concentrations of NO 2 in the start year and c 2 is in the follow year 3. Results and Discussion Monthly tropospheric NO 2 during the period October 2004 to March 2013 obtained from OMI to investigate the monthly variations.
Figure 2 shows the monthly average concentrations of NO2 over three sites, Baghdad, Basrah and Erbil.It is obvious that dominant species show considerable seasonal variations.

Figure ( 4 )
Figure (4) Whisker plots of NO2 variations over (a) Baghdad (b) Basrah and (c) Erbil during the period from October 2004 to March 2013.

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Table ( 1
(1)nnual increase of NO 2 concentration From Table(1)it is found increasing in NO 2 concentrations during the study period.The maximum increase in NO 2 is about (11.53 % per year) at Erbil and the minimum is about (7.42% per year) at Baghdad Conclusions Monthly tropospheric NO 2 columns over three major Iraqi cities have been recorded using AURA OMI.It is observed that