6dos% of city enterprises produce, supply or support the production of metal step three5 . Interestingly, although Novokuznetsk is not a city with coal-oriented economy, coal is actively used kauniita Nicaraguan naiset as input in its production of metal as conversion of most or all metal ores to usable metal is highly energy intensive. Metal production facilities use coal to provide energy and the metals are being produced by conversion of coal to coke, where both processes emit substantial NO2 emissions in the atmosphere. 2 emissions from a previous study 36 . Notably, NO2 emissions from metal production of West-Siberian Metal Plant (WSMP) account for 8cuatro.2% of all the gaseous pollutants of . Most importantly, we found high correlation (r = 0.76) between inventory-based NO2 emissions from WSMP 36 and our annual NO2 tropospheric estimates from OMI and, where even higher correlation (r = 0.84) was discerned between WSMP NO2 emissions and coal production from Fig. 4 . These findings clearly indicate that metal manufacturing of Novokuznetsk is based on coke-intensive input, thereby pointing on a key role of coal in these emissions.
Dialogue
The sensitivity of tropospheric NO2 (measured by OMI) to the mining, production, and transportation of coal in Russia’s largest coal basin (Kuzbass) was demonstrated for the first time. A major long-term tropospheric NO2 anomaly was revealed over Kuzbass (3.22 ± 0.52 ? 10 15 molecule/cm 2 ) in the period 2005–2018, indicating substantial gaseous pollution over the region. The anomaly was attributed to the Kuzbass coal basin, based on moderate agreement identified between (1) the spatial distributions of NO2 and night lights originating from the cluster of coal mines and cites, as well as by (2) the correlation between inter-annual coal production and annual NO2 levels in Kuzbass (r ? 0.60). Unlike the global trend of NO2 reduction over urban areas (including Siberian cities), NO2 substantially increased over Kuzbass in the 2010–2014 and 2015–2019 periods (7% ± 5% and 15% ± 8%, respectively, relative to a baseline period of 2005–2009). The total coal production in Kuzbass was 888, 993, and 1,151 million tons in the periods 2005–2009, 2010–2014, and 2015–2019, respectively. Production in the two latter periods increased by 11% and 30%, respectively, compared with the baseline period. Remarkably, such increases seem to be strikingly proportional to our reported NO2 increments over the Kuzbass basin during the same period. 2 and coal production, a
0.5%–0.6% increase in the NO2 concentration in the region, where some portion of this increase may have been offset by regulations limiting emissions.
From regional perspective, the demonstrated association between tropospheric NO2 with coal mining and processing activities over the largest coal basin in Russia is valuable, given the limited opportunity to otherwise assess the environmental impacts of coal-related activities in developing/emerging economies such as Russia, where official information is often inaccurate and atmospheric observations are scarce. These first estimates of substantial tropospheric NO2 increases over Kuzbass can encourage national and regional policy makers to formulate new pollution mitigation strategies to assess and to minimize the local population’s exposure to the adverse cardiovascular and respiratory effects of tropospheric NO2 and also O3, as NO2 is a precursor of O3. Moreover, elevated atmospheric NO2 may cause indirect adverse environmental effects such as nitrogen enrichment of water bodies via deposition, which compromises the safety of drinking water as well 37 .
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Our findings are novel at a global level, as most existing spaceborne studies focusing on coal mining have reported increases in atmospheric CH4 6 , 7 , 38 , 39 . Although we demonstrated that spaceborne observations of NO2 can be utilized to attribute NO2 pollution to previously unreported coal mining and processing over large exploited coal basins, the hypothesis that coal mining itself can be a major source of NO2 emissions should be evaluated. The tropospheric NO2 anomaly over Kuzbass could be driven both by direct nitrogenous outgassing from coal mining (e.g., scraping and fracturing) and indirect nitrogenous emissions from coal mining and processing. Such indirect nitrogenous emissions originate from the inefficient compression-ignition diesel engines of coal mining equipment (excavators), coal transportation vehicles (haul trucks) and from nearby facilities for processing coal. Notably, the combustion of heavy fuel by the haul trucks deployed in Kuzbass has already been questioned from an ecological viewpoint 19 . Although new heavy machinery meeting Euro-3 and Euro-4 standards is being delivered to Kuzbass, there remains an abundance of inefficient diesel-fueled equipment prone to emitting NOx 19 . Moreover, as preliminarily indicated, such indirect coal emissions can stem from manufacturing of steel, which uses coke in the production, thereby generating various indirect air pollutants including NO2.