Tropospheric NO 2 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 NO 2 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 NO 2 over Ekibastuz, whereas the regions of Almaty and Shymkent showed increasing trends due to industrial growth. The seasonal pattern of the NO 2 concentration shows a difference between three industrial cities of Almaty, Shymkent, and Ekibastuz versus the rest of Kazakhstan. In these three cities, a NO 2 maximum is found during wintertime, which we attribute to seasonality of emissions associated with electricity production and the longer chemical lifetime of NO 2 in winter. In contrast, in Astana and the rest of Kazakhstan, the NO 2 concentration reaches a maximum in the summer.
Satellite observations of the Ozone Monitoring Instrument (OMI) for tropospheric sulfur dioxide (SO 2) and formaldehyde (HCHO) column mass densities (CMD) are analyzed for the period 2005-2016 over the atmosphere of Kazakhstan. Regarding SO 2 the major hot spots relate to regions with high population and large industrial facilities. Such an example is the city of Ekibastuz that hosts the biggest thermal power plants in the country and exhibits the higher SO 2 CMD at national level. The annual average CMD in Ekibastuz reaches 2.5 × 10 −5 kg/m 2 , whereas for the rest of the country respective values are 6 times lower. Other hotspots, mostly urban conglomerates such as Almaty and Nur-Sultan, experience high CMDs of SO 2 in particular years, such as 2008. One of the main reasons for this behavior is the financial crisis of 2008, forcing the application of alternate heating sources based on cheap low-quality coal. Regarding HCHO, an oxygenated Volatile Organic Compound (VOC), the main hot spot is noticed over the city Atyrau, the oil capital of the country where two massive oil fields are located. The highest HCHO CMD (9 × 10 15 molecules/cm 2) appears in the summertime due to secondary production as a result of the photo-oxidation of VOCs emitted by industrial sectors, oil refinery plants and vehicles. Strongly elevated HCHO amounts are also observed in Nur-Sultan in 2012 that could be due to the residential coal combustion and vehicle exhaust under poor winter dispersion conditions. Significant reductions in HCHO observed between 2012 and 2015 can be attributed to two significant measures implemented in the country in 2013 that aimed at the improvement of air quality: the introduction of the emission trading system (ETS) for greenhouse gases and Euro-4 standards for new vehicles entering the national vehicle fleet. Sulfur dioxide (SO 2) is emitted to the atmosphere from fossil fuel burning, mainly coal and residual oil as well as from volcanic eruptions. The atmospheric residence lifetime of sulfur dioxide is 2-7 days, and its main loss mechanism in the atmosphere is oxidation to form sulfuric acid (H 2 SO 4). Atmospheric formaldehyde (HCHO) is mainly formed through the oxidation of different volatile organic compounds (VOCs) present in the atmosphere 1. Apart from the photochemical oxidation, which contributes to 70-90% of the vertical column density (CMD) of atmospheric HCHO in urban areas 2, combustion, biogenic activities and biomass burning account for the majority of primary emissions. The loss of HCHO occurs by photolysis and reaction with hydroxyl radical (OH) 1. HCHO levels play a significant role in controlling the ozone concentrations in urban areas since formaldehyde photolysis is an important source of hydroperoxy radicals 1. The hydroperoxy radicals contribute to the ozone production cycle. Long term monitoring of the atmospheric formaldehyde and sulfur dioxide by satellites may assist in determining the major sources of these compounds.
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