Evaluation of NO2 column variations over the atmosphere of Kazakhstan using satellite data Zhuldyz Darynova,a Aigerim Maksot,b Lyazzat Kulmukanova,b Milad Malekipirbazari,c Hamed Sharifi,a Mehdi Amouei Torkmahalleh,b,d,* and Tracey Hollowaye aRizgard Payesh Asman LLP (Sky Aerosol Monitoring LLP), Department of Air Pollution Modelling, Tehran, Iran bNazarbayev University, School of Engineering, Department of Chemical Engineering, Chemical and Aerosol Research Team, Astana, Kazakhstan cBilkent University, Department of Industrial Engineering, Ankara, Turkey dNazarbayev University, Environment and Resource Efficiency Cluster, Astana, Kazakhstan eUniversity of Wisconsin–Madison, Nelson Institute for Environmental Studies and the Department of Atmospheric and Oceanic Sciences, Madison, Wisconsin, United States Abstract. Tropospheric NO2 concentrations obtained from the measurements of the Ozone Monitoring Instrument on board the NASA Aura satellite from 2005 to 2016 were studied to identify major NO2 emission hot spots, trends, and seasonal variations over Kazakhstan. Emission hot spots are observed over the locations of thermal power plants (Ekibastuz) and major urban and industrial regions (Almaty and Shymkent), as well as the capital city (Astana). Some decreasing trends have been observed for NO2 over Ekibastuz, whereas the regions of Almaty and Shymkent showed increasing trends due to industrial growth. The seasonal pattern of the NO2 concentration shows a difference between three industrial cities of Almaty, Shymkent, and Ekibastuz versus the rest of Kazakhstan. In these three cities, a NO2 maximum is found during wintertime, which we attribute to seasonality of emissions associated with elec- tricity production and the longer chemical lifetime of NO2 in winter. In contrast, in Astana and the rest of Kazakhstan, the NO2 concentration reaches a maximum in the summer. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.JRS.12.042610] Keywords: NO2; NASA Aura Satellite; Kazakhstan; Almaty; Astana; power plants. Paper 180367SS received May 28, 2018; accepted for publication Sep. 28, 2018; published on- line Oct. 25, 2018. 1 Introduction Nitrogen dioxide (NO2) and its precursor nitric acid (NO) together are known as nitrogen oxides (NOx), which play a vital role in the tropospheric chemistry. NOx is a precursor of tropospheric 1 ozone and nitrate particulate matter, both of which affect air quality and climate. NOx concen- trations in the troposphere are highly variable in both space and time, reflecting its short chemical 2 lifetime in the atmosphere and its nonuniform distribution. The lifetime of NO2 was reported to be ∼6hin summer, ∼6 to 12 h in spring and fall, and 12 20 h in winter, due to the variability in the photolysis rate and water vapor content in the atmosphere.3 Emissions of NOx come from both anthropogenic and natural sources. Elevated temperatures associated with combustion combine ambient N2 and O2 to form NO, which oxidizes to NO2. Major contributors to global NOx emissions include industrial activities, electricity generation, transportation, and prescribed burnings.4 Natural phenomena, such as lightning, wildfires, and 5 soil microbial activities, contribute to NOx emissions. This study focuses on NOx emissions in Kazakhstan, which is the ninth largest country in the world at 2.72 million km2, one of the top coal and oil producing countries in the world,6 while *Address all correspondence to: Mehdi Amouei Torkmahalleh, E-mail: [email protected] 1931-3195/2018/$25.00 © 2018 SPIE Journal of Applied Remote Sensing 042610-1 Oct–Dec 2018 • Vol. 12(4) Darynova et al.: Evaluation of NO2... maintaining one of the lowest population densities of any country at 7 per km2.7 Over 50% of the Kazakhstan’s energy is supplied by coal, and the oil sector is the largest determinant of the country’s economic growth (ibid). Between 2002 and 2016, the gross domestic product of Kazakhstan has increased sixfold. In 2014, the highest per capita household coal consumption occurred in Poland (165 kgoe/cap), followed by Kazakhstan (157 kgoe/cap), and Mongolia (104 kgoe/cap).8,9 Kazakhstan experiences unique metrological conditions where the tempera- ture in winter time may go down to −40°C in the north. Characterizing NOx emissions in this large, energy-intense country bears relevance to air quality and climate impacts for the region, country, and world. The World Bank found that the air quality monitoring network in Kazakhstan may experience unrepresentative sampling because the number of monitoring sites are low, and the selection of monitored pollutants does not comply with recognized priority 10 pollutants. To address this data need, we apply satellite retrievals of NO2 to assess NOx trends and spatial variability in Kazakhstan. Long-term observations of satellite NO2 columns can constrain NOx emission inventories and significantly reduce model uncertainties in simulations studies.11 Prior studies using satellite data indicate that NO2 levels decreased sharply over the last decade in many countries, such as the United States, Japan, Australia, New Zealand, and those in Western Europe.12–15 This decrease resulted from a combination of the implementation of emission control devices on ther- mal power plants, the shuttering of inefficient plants, and stricter vehicle emission standards.16 17 Liu et al. found that a high NOx concentration does not necessarily correspond to a long life- time, and the correlation between NOx lifetime and NO2 tropospheric vertical column density is 2 rather low (R ¼ 0.22), probably due to the complex NOx chemistry, which is also affected by meteorological and chemical variability, such as variations in UV flux, water vapor, and VOC levels.18 Currently, only a few studies regarding the atmosphere of Central Asia are available. In par- ticular, no studies were found in the literature that investigates NO2 concentrations variability in Kazakhstan. The objective of this study was to examine the temporal evolution of tropospheric NO2 in four major cities of Kazakhstan including Astana, Shymkent, Almaty, and Ekibastuz from 2005 to 2016 using the data from ozone monitoring instrument (OMI) launched on the NASA Aura satellite in July 2004. 2 OMI Tropospheric NO2 Columns Our study uses data from OMI to assess air quality patterns and trends in Kazakhstan. OMI is a nadir-viewing wide-field imaging spectrometer data on the board of NASA Aura satellite. Its ground resolution is 13 km × 25 km, spectral and spatial detection is 780 × 576 pixels, respectively, and can detect UV with wavelength 350 to 500 nm. The instrument observes Earth’s backscattered radiation in the ultraviolet and a visible range of 350 to 500 nm with a wide-telescope feeding two imaging grating spectrometers. Aura was launched on July 14, 2004, into a Sun-synchronous polar orbit at ∼705-km altitude with a local equator crossing time of 13:45 in the ascending node.3,19 The hyperspectral capabilities of the instrument can improve the accuracy and precision of the total ozone concentration. Also, it allows for accurate radiometric and wavelength selfcali- bration over the long term. The Dutch OMI NO2 (DOMINO) retrieval algorithm consists of three steps. First, the slant columns of NO2 are obtained from the OMI reflectance spectra in the 405- to 465-nm window using the DOAS technique.20 Second, the stratospheric and tropospheric contributions to the OMI NO2 slant columns are separated by assimilating the slant columns of a global chemistry and transport model.21,22 We used monthly average level-3 product. Finally, tropospheric slant column is converted to a vertical column with the tropospheric air mass factor. The tropospheric NO2 column retrievals used are from the version-2 DOMINO data product for OMI22 obtained through the TEMIS25 website. The ground pixel size of the OMI retrievals is 13 to 24 km with a daily global coverage. This study employs the monthly average level 3 OMI × NO2 product available at 0.25 deg 0.25 deg because these data are gridded files on a fixed grid. One grid cell (0.25 deg × 0.25 deg) falls in each city. Since cities are not perfectly square Journal of Applied Remote Sensing 042610-2 Oct–Dec 2018 • Vol. 12(4) Darynova et al.: Evaluation of NO2... shaped, at the edges there might be some uncertainties. In the case of Almaty, which is sur- rounded by mountains, the grid cell did not cover mountains. 3 Study Area We focus on the four major cities of Kazakhstan including Astana, Shymkent, Almaty, and Ekibastuz from 2005 to 2016. These four cities are among most populated and largest urban areas where potential NO2 emissions exist. Almaty (43.22°N, 76.85°E) is located in the valley of big and small Almatinka rivers at the foot of Trans-Ili Alatau mountains (Fig. 1). The city is surrounded by mountains and hills, limit- ing horizontal movement of air. Wind generally blows southward during the day, bringing cold and polluted air from the North and northward at night.23 The population of Almaty has 24 increased from 2005 to 2016 by 42% (Fig. 2). Sources of NO2 in Almaty include thermal power plants, motor vehicles, boilers from military garrisons of regional operational units of the Ministry of Defense, boiler companies, and building material manufacturing. Emissions 23 from transportation account for ∼80% of NOx emissions in Almaty. As of 2010, over 500,000 vehicles were registered in Almaty, of which 54.6% were produced from 1996 to 2003, 20.9% from 2003 to 2008, and only 2.4% recently manufactured, suggesting that engines do not comply with modern emission standards.23 Shymkent (42.34°N, 69.69°E) is an industrial city with the population of 902,000 by 2016. The city population has increased from 2005 to 2016 by 68% (Fig. 3).25 The main sources of NO2 come from stationary and mobile sources (Fig. 4). The stationary sources include lead, petrochemical, chemical, thermal power plants, and uranium mining enterprises.