Impact of air pollutants on non-accidental mortality and burden of death of residents after air pollution control in main urban districts of Lanzhou

Background Air pollution is a major environmental risk factor that affects human health.

Objective This study evaluates the impact of air pollution on non-accidental mortality and burden of death of residents in the main urban districts of Lanzhou after implementing air pollution control measures.

Methods The monitoring data of air pollutants SO₂, NO₂, and PM₁₀ from 2004 to 2011 (before air pollution control), and the monitoring data of air pollutants SO₂, NO₂, PM_2.5, PM₁₀, CO, and O₃, meteorological variables, and death cause of residents from 2014 to 2018 (after air pollution control) in four main urban districts (Chengguan District, Qilihe District, Xigu District, and Anning District) of Lanzhou City were collected and used to calculate total non-accidental mortality and concentrations of air pollutants. The impact of air pollutants on non-accidental mortality of residents was analyzed by generalized additive models, after controlling time trends, seasonal effects, meteorological factors, day-of-the-week effect, and other factors. The burden of death attributed to air pollution was quantitatively evaluated by Poisson regression proportional risk models.

Results From 2004 to 2011, the annual average concentrations of SO₂, NO₂, and PM₁₀ in the four urban districts of Lanzhou were 61.58, 45.47, and 154.97μg·m^-3, respectively. From 2014 to 2018, the total number of non-accidental mortality was 79 284, with an average of 43 nonaccidental deaths per day, and the average annual concentrations of SO₂, NO₂, PM_2.5, PM₁₀, CO, and O₃ were 21.58μg·m^-3, 54.42μg·m^-3, 52.67μg·m^-3, 124.84 μg·m^-3, 1.41 mg·m^-3, and 87.40 μg·m^-3, respectively. After the air pollution control (2014-2018), the daily average concentrations of SO₂ and PM₁₀ decreased, while the concentration of NO₂ increased. There was a positive correlation between non-accidental mortality and each of the selected six air pollutants, among which the correlation with SO₂ was the strongest (r=0.906) and the correlation with NO₂ was the weakest (r=0.048). The risk of non-accidental mortality attributed to SO₂ and NO₂ reached the highest value with a 2-day lag, and their relative risks were 1.002 13 (95% CI: 1.001 35-1.002 90) and 1.000 59 (95% CI: 1.000 17-1.001 02), respectively. The risk attributed to PM₁₀ and PM_2.5 reached the highest value on the current day, and their relative risks were 1.000 12 (95% CI: 1.000 04- 1.000 20) and 1.000 48 (95%CI: 1.00017-1.000 79), respectively. Each 10 μg·m^-3 increase of SO₂, NO₂, PM₁₀, and PM_2.5 concentrations was associated with an increase in the risk of non-accidental mortality of residents by 2.15%, 0.59%, 0.12%, and 0.49%, respectively. According to the air quality guidelines proposed by the World Health Organization (WHO), the numbers of deaths attributable to SO₂, NO₂, PM₁₀, and PM_2.5 were 263, 683, 827, and 1 674, respectively, and their attributable fractions were 2.56%, 6.65%, 8.06%, and 16.30%, respectively. According to the second-level annual average concentration limits stipulated in the Ambient air quality standard (GB 3095-2012), the numbers of deaths attributable to NO₂, PM₁₀, and PM_2.5 were 683, 434, and 698, respectively, and their attributable fractions were 6.65%, 4.22%, and 6.79%, respectively.

Conclusion After implementing the air pollution control measures in Lanzhou, air pollutants SO₂, NO₂, PM₁₀ and PM_2.5 still have an impact on non-accidental mortality of residents, especially SO₂, and on residents' burden of death, especially PM_2.5.