Regulation of open straw burning and residential coal burning around urbanized areas could achieve urban air quality standards in the cold region of northeastern China

Abstract

Air quality issues in Northeast China are concerning due to the significant seasonal atmospheric pollution and typical climatic, geographic and industrial structure characteristics of the area. However, urban air quality managers are having great difficulty achieving targeted pollution control goals in the time allotted due to limited studies in the region. In this study, using the city of Siping in Jilin Province as a case study, we analysed the cause of seasonal atmospheric pollution, developed a high-resolution emissions inventory for major atmospheric pollutants and simulated urban air quality improvements under projected emission control scenarios to select a reasonable source control scheme to inform urban air quality management planning in the region. Years with available air quality data (2014–2020) were divided into three periods, i.e., a weak control period (WCP: 2014–2017), an enhanced control period (ECP: 2018–2019) and the COVID-19 period (CDP: 2020). The annual PM_2.5, PM₁₀, SO₂ and NOx emissions varied by 62∼46 μg·m⁻³, 103∼76 μg·m⁻³, 27∼22 μg·m⁻³ and 46∼41 μg·m⁻³, respectively, during the WCP; the emissions decreased to 37 μg·m⁻³, 69 μg·m⁻³, 11 μg·m⁻³ and 34 μg·m⁻³, respectively, during the ECP and to 33 μg·m⁻³, 61 μg·m⁻³, 11 μg·m⁻³ and 33 μg·m⁻³, respectively, during the CDP, which reached the limits of the Ambient Air Quality Standard of China (level II, 35 μg·m⁻³, 70 μg·m⁻³, 60 μg·m⁻³ and 50 μg·m⁻³). The PM_2.5 and PM₁₀ indices exceeded the standards, mainly in late autumn (October and November) and in the middle of winter (January and February). Based on comprehensive data analysis of the spatiotemporal air quality and the local high-resolution emissions inventory, straw burning, stationary combustion (especially for coal burning) and vehicle emissions were the main pollution sources in late autumn, and continuous adverse weather conditions were the dominant factors in severe pollution days during the middle of winter. In addition, the urban air quality of Siping was also affected by pollutant transport from the northwest (the city of Songyuan in Jilin Province), northeast (the city of Changchun in Jilin Province) and south (the city of Tieling in Liaoning Province) according the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Strict straw-burning policy was implemented in autumn during the ECP and CDP, which significantly improved the air quality from that of the WCP, with an AQI reduction of 31.58 %. However, the planned burning policy was not well-implemented, resulting in more days of moderate or heavy pollution. Using 2017 as the base year, scenarios were simulated in which feasible source control measures were set (namely, straw-burning control, the elimination of small boilers in urbanized areas, staggered peak heating measures and a 50 % reduction in residential bulk coal burning around urbanized areas and suburban areas), and the concentrations of PM_2.5 and PM₁₀ were projected to decline by more than 29.79 %, meeting the urban air quality standards. This study highlights the importance of combining straw burning regulation in no-burning areas, limited burning areas and residential coal-burning substitution around urbanized areas to improving the air quality in cold regions.