| Objective: Air pollution control is a complex and systematic project.Energy for the central heating service in main urban areas of Lanzhou has been modified from coal to natural gas since the winter of 2012,and the construction of air quality automatic monitoring system in Lanzhou has been finished and put into service gradually since June 2013.PM2.5 was included in the monitoring range.Therefore,this study intends to i vesti ate the cha e of reside ts' a bie t PM2.5 exposure level in main urban areas of Lanzhou from 2013 to 2016,and estimate premature mortalities due to PM2.5 exposure and mortality benefits for different scenarios.Meanwhile,polycyclic aromatic hydrocarbons(PAHs)concentration from 2015 to 2016 was detected to evaluate the PAHs exposure level and health risk for residents in main urban areas of Lanzhou,and possible sources of PAHs were distinguished and then we want to provide the basis for the next air pollution control measures.Methods:(1)PM2.5 monitoring data in main urban areas of Lanzhou from September 2013 to August 2016 were collected,and ambient PM2.5 population-weighted exposure concentration was calculated to describe the cha e of reside ts' a bie t PM2.5 exposure level after the “coal to gas” project in main urban areas of Lanzhou.According to the secondary limit in Chinese Ambient Air Quality Standard(GB 3095-2012)for PM2.5,reside ts' a bie t PM2.5 exposure level was evaluated.The IER odel was used to evaluate reside ts' health effects associated with PM2.5 exposure,and health economic benefit via reducing PM2.5 exposure level was estimated by WTP.(2)Portable air sampler was used to collect ambient PM2.5 in main urban areas of Lanzhou,and GC-MS was available to analyze the contents of PAHs in PM2.5.Mann-Whitney U test was chose to analyze the significant impact of the central heating on PM2.5-bound PAHs.TEQ was utilized to quantitatively describe health hazard of PAHs through respiratory exposure,and inhalation cancer risk and loss of life expectancy were also estimated.Results:(1)From September 2013 to August 2016,PM2.5 population-weighted exposure level of residents in main urban areas of Lanzhou was 57.5?g/m~3(11~457?g/m~3).According to Chinese Ambient Air Quality Standard(GB 3095-2012)for PM2.5,there were 878 days(80.1%)meeting the secondary limit,Summer > Spring >Autumn > Winter,and the number of days not up to standard in Winter made up to 77.9% of the total days not comfort to the secondary limit.(2)PM2.5 exposure level of residents had a significant decrease after the “coal to gas” project in main urban areas of Lanzhou,but there was still a distance between current exposure level and standard.Taking the annual average PM2.5 exposure concentration in 2016 as an example,the value was 1.38 times of the national standard,4.38 times of WHO target.(3)Taking PM2.5 exposure level in 2014 as a baseline,910 cases and 2266 cases of excess death could have been avoided if PM2.5 concentrations in main urban areas of Lanzhou had met the national standard and WHO target,respectively.Health economic benefit associated will be 82 million RMB and 203 million RMB,accounting for 0.04% and 0.1% of Lanzhou GDP in 2014,respectively.(4)PM2.5-bound PAHs exposure level of residents in main urban areas of Lanzhou currently was 778.3?g/m~3(91.4~1910.9?g/m~3),among which 16 priority control PAHs and 8 carcinogenic PAHs were 772.4?g/m~3(91.2~1892.8?g/m~3)and 495.2?g/m~3(40.8~1156.6?g/m~3),respectively.The impact of the central heating on PAHs had statistical significance(p < 0.05)and the exposure level of residents in the heating period was higher than that in non-heating period.(5)The predominant PAHs in PM2.5 were lower molecular weight compounds(two-and three-ringed PAHs),but only 3.3%~10.4% of higher molecular weight PAHs.The diagnostic ratio method for identifying the PAH source found petroleum,coal and biomass combustion and vehicular traffic were probably the main sources of PAHs in the PM2.5 from main urban areas of Lanzhou.(6)The mean for the whole monitoring period was 19.4?g/m~3(1.97~61.80?g/m~3),and the ILCR for a lifetime of 70 years averaged 1.68 10-3(1.7 10-4~5.4 10-3),hi her tha WHO's reco e ded value(10-6),and then loss of life expectancy by inhalation exposure in main urban areas of Lanzhou was 7.3 days.Conclusion: PM2.5 exposure level of residents has a significant decrease after the Government transformed coal to natural gas for the central heating service in main urban areas of Lanzhou.However,it is still a high exposure level and has significant health risks of PM2.5 and relative PAH currently.Therefore,it is still a very important public health problem needed to solve for the Government to explore air pollution control measures suiting for the new situation in Lanzhou so as to reduce the health risks of exposure. |
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