| There are different types of air pollutants,such as particulate matter(PM)of various sizes,chemical constituents and various gaseous pollutants.Ambient air pollution ranks the fourth leading risk factor for early death worldwide.Increasing evidence of epidemiological studies has shown the associations between air pollutants and morbidity and mortality of respiratory diseases.It has been suggested that children are more sensitive to the effects of air pollutants than adults due to their biological and behavioral characteristics.About 300 million children are exposed to hazardous levels of outdoor air pollution globally.In addition,the burden of respiratory diseases in children is huge.Time-series study is widely used to evaluate the acute health effects of air pollutants internationally,and it provides a lot of information support for the formulation of air quality guidelines and standards.Several multicity studies conducted in all-age population have evaluated the associations between air pollutants and respiratory hospital visits,however,time-series studies focused on hospital visits for respiratory disease among children have been always based on a single city.The inconsistent results in these single-city studies might be due to inherent differences in patient characteristics,pollution levels and compositions,geographical locations and meteorological conditions,etc.Moreover,only very few single-city studies have shown the exposure-response relationships of respiratory outpatients with air pollutants among children.A few previous epidemiological studies have explored the potential association of size-fractionated particle number concentrations(PNCs)and PM constituents with the hospital visits of respiratory diseases among children.There has been no clear evidence to recognize the key size-fractionated PMs and constituents that pose a greater threat to the respiratory health of children.Additionally,although a large amount of literature has reported the independent effects of temperature,relative humidity and air pollutants on health,very few studies have clarified the effects of air pollutants on respiratory outpatient visits among children at different temperature or relative humidity levels and their possible interactions.Therefore,it is important to evaluate the effect of short-term air pollutants exposure on respiratory disease outpatients among children at a multicity level in order to provide systematic scientific information for the evaluation of the hazard effects of air pollutants,formulation of prevention and control measures and policy revision.In summary,this study intends to select five representative cities in China.Firstly,explore the relationship between PM and the respiratory outpatient visits among children,and further determine the key size-fractionated PNCs and constituents in different cities.Moreover,clarify the effect of gaseous pollutants on the respiratory outpatient visits among children.Finally,examine the effect of PM and gaseous pollutants on respiratory outpatient visits among children under different temperature and relative humidity conditions.And in each part of the study,clarify the corresponding exposure-response relationship and the effect difference between the subgroups.Part 1 Association between ambient particulate matter and respiratory outpatient visits among children: A multi-city time-series study1.1 Effects of fine,inhalable and coarse particulate matters on respiratory outpatient visits among childrenObjective: To investigate the association between short-term exposure to ambient PM and respiratory outpatient visits among children at a multicity level.Methods: Five representative cities in China were included in this study,including Guangzhou,Shanghai,Wuhan,Beijing and Xining.A time-series study was conducted among children aged 0-14 years in five Chinese cities from 2013 to 2018.City-specific effects of fine particles(aerodynamic diameter ? 2.5 ?m,PM2.5),inhalable particles(aerodynamic diameter ? 10 ?m,PM10)and coarse particles(between 2.5 and 10 ?m in diameter,PM10-2.5)were estimated for time lags of zero up to seven previous days using the overdispersed generalized additive models after adjusting for time trends,meteorological variables,day of the week and holidays.The exposure-response curves were evaluated using a cubic regression spline.Meta-analyses were applied to pool the overall effects.Results: A total of 3,005,793 respiratory outpatients(ICD-10: J00-J99)among children from 2013 to 2018 were included in the study.The moving average lag effects of PM showed higher estimates than that of single-day exposure,and PM2.5,PM10 and PM10-2.5 at lag 07 produced the largest estimates.Each 10 ?g/m3 increment in PM2.5,PM10 and PM10-2.5 at lag 07 was associated with a 1.39%(95% CI: 0.38%,2.40%),1.10%(95% CI: 0.38%,1.83%)and 2.93%(95% CI: 1.05%,4.84%)increase in total respiratory outpatients,respectively.An exposure-response relationship was observed except for PM2.5 in Beijing and PM10 and PM10-2.5 in Shanghai.The overall effects of PM were significantly associated with respiratory outpatients among children,even at PM2.5 and PM10 levels below the Chinese Ambient Air Quality Standards(CAAQS)(GB3095-2012)Grade II.Compared with the warm season,the PM effect was significantly higher in the transition and cold seasons(P<0.05),and showed differences in the seasonal effects between northern and southern cities.The effects of PM were stronger in the cold season in 3 southern cities,while it was stronger in the transition season in 2 northern cities.There were no significant differences in age,sex and specific respiratory subgroups.The effects of PM2.5 and PM10 on respiratory outpatients remained significant after adjustment for gaseous pollutants with a correlation coefficient <0.6 at the same lag.Conclusions: Short-term PM exposures were dose-responsive associated with increased respiratory outpatient visits among children,even for PM2.5 and PM10 levels below CAAQS Grade II in certain cities.1.2 Effects of size-fractionated fine particle matter and its constituents on respiratory outpatient visits among childrenObjective: To investigate the association between short-term exposure to fine PM with different sizes and its constituents and respiratory outpatient visits among children.Methods: We obtained size-fractionated PNCs and constituents in Guangzhou,Wuhan and Shanghai,respectively.A time-series study was conducted among children aged 0-14 years.We used overdispersed generalized additive models to estimate the associations of size-fractionated PNCs and constituents of fine particulate matter with the daily respiratory outpatients for time lags of zero up to seven previous days after adjusting for time trends,meteorological variables,day of the week and holidays.A cubic regression spline was applied to evaluate the exposure-response curves.Except for the single-constituent model,the constituent-PM2.5 adjustment model and constituentresidual model were built to control for the potential confounding effect of PM2.5 and its collinearity with the remaining constituents,respectively.Results: All the size-fractionated particles with a diameter ? 2.5 ?m in Guangzhou and Wuhan were significantly associated with the respiratory outpatients among children,and no significant differences were observed.While the size-fractionated particles with a diameter ? 0.1 ?m in Shanghai exhibited the strongest risk effects.All the above effects of size-fractionated particles on outpatients were dose-responsive.Moreover,the effect of constituents in each city varied greatly.In Guangzhou,except for the effects of ammonium and magnesium,other constituents' estimates were statistically significant.Among them,lithium,iron and manganese had stronger effects.The black carbon at 370 nm,manganese,zinc,scandium,titanium and calcium had significant effects in Wuhan,while the estimates of organic carbon,elemental carbon,chloride ion,manganese,and selenium were stronger in Shanghai.All the statistically significant constituents had a dose-response relationship with respiratory outpatient visits among children.Conclusions: All the size-fractionated particles with diameter ? 2.5 ?m in Guangzhou and Wuhan and size-fractionated particles with diameter ? 0.1 ?m in Shanghai were dose-responsive associated with increased respiratory outpatient visits among children.The effect of constituents in each city varied greatly and a variety of constituents showed adverse health effects on the respiratory outpatient visits among children in a dose-responsive manner.Part 2 Association between ambient gaseous pollutants and respiratory outpatient visits among children: A multi-city time-series studyObjective: To investigate the association between short-term exposure to gaseous pollutants and respiratory outpatient visits among children at a multicity level.Methods: Consistent with the research subjects contained in Part 1,section 1.1.A time-series study was conducted among children aged 0-14 years in five Chinese cities(Guangzhou,Shanghai,Wuhan,Beijing and Xining)from 2013 to 2018.City-specific effects of gaseous pollutants(NO2,SO2,CO and O3)were estimated for time lags of zero up to seven previous days using the overdispersed generalized additive models after adjusting for time trends,meteorological variables,day of the week and holidays.Cubic regression splines were used to evaluate the exposure-response relationships.We further conducted stratified analysis by gender,age,season and disease subtype.Meta-analyses were applied to pool the overall effects.Results: The moving average lag effects of 4 gaseous pollutants showed higher estimates than that of single-day exposure,and NO2,SO2 and CO at lag 07,and O3 at lag 04 produced the largest estimates.Each 10 ?g/m3 increment in NO2 and SO2 at lag 07 and O3 at lag 04,and per 0.1 mg/m3 increase in CO at lag 07 corresponded to increments of 4.61%(95% CI: 3.29%,5.94%),6.73%(95% CI: 1.79%,11.91%),0.94%(95% CI: 0.11%,1.77%)and 0.87%(95% CI: 0.52%,1.22%)in total respiratory outpatients,respectively.An exposure-response relationship was observed except for SO2 and O3 in Xining.The overall effects of all 4 gaseous pollutants were significantly associated with total respiratory outpatients among children,even at their levels below the CAAQS Grade II.NO2 had a stronger impact on children aged ? 4 years,which was significantly higher than that on children aged < 1 year(P<0.05).In addition,NO2 and SO2 had a stronger effect in the cold season,while CO had a stronger effect in the cold and transition seasons compared with that in the warm season(P<0.05).Moreover,the effect of O3 had a stronger effect in the transition and warm seasons compared with that in the cold season(P<0.05),and showed different seasonal effects between northern and southern cities.The effects of O3 were stronger in the transition season in 3 southern cities,while it was stronger in the warm season in 2 northern cities.There were no significant differences in sex and specific respiratory subgroups.The effects of NO2 and O3 on respiratory outpatients remained significant after adjustment for other pollutants(P<0.05).Conclusions: Short-term gaseous pollution exposures were dose-responsive associated with increased respiratory outpatient visits among children,even for their levels below CAAQS Grade II in certain cities.Part 3 Interactive effects of ambient temperature,relative humidity and air pollutants on respiratory outpatient visits among childrenObjective: To explore the effects of air pollutants on respiratory outpatient visits among children at different temperature or relative humidity levels and their possible interactions.Methods: The research subjects were the same as those in Part 1,Section 1.1.We used the overdispersed distributed lag non-linear models to analyze the city-specific effects of temperature and relative humidity on respiratory outpatient visits among children.The relative risk(RR)was calculated for respiratory outpatient visits among children at low temperature/relative humidity(P5 and P25)and high temperature/relative humidity(P75 and P95),compared with the medium temperature/relative humidity(P50).Moreover,exposure-response relationships were also evaluated.Response surfaces and stratification methods were performed to obtain the interactive effect of temperature or relative humidity and air pollutants.The temperature/relative humidity was categorized into low,medium,and high levels using the 25 th and 75 th percentiles of the city-specific daily mean temperature/relative humidity data as cutoffs.The effects of air pollutants at low(<P25),medium(P25-P75),and high(>P75)temperature/humidity and possible interactions between them were calculated.Subgroup analyses were conducted by age,gender,and subgroups of diseases.We applied meta-analyses to pool the overall effects.Results: Compared with the medium temperature(P50),high temperature(P75)was generally associated with a significant increase in the number of outpatients among children,while low temperature(P5)was associated with a significant decrease in the number of respiratory outpatients among children.In addition,there were significant nonlinear exposure-response relationships in all cities.There was no significant difference in the effect of PM at low temperature(<P25),medium temperature(P25-P75)and high temperature(>P75)on the respiratory outpatients among children.Compared with medium temperature,NO2 at low and high temperatures and CO at low temperature showed a greater effect and had a significant interactive effect(Pinteraction<0.05).Compared with low temperature,O3 had a more significant effect at medium temperature and high temperature and had a significant interactive effect(Pinteraction<0.05).Children aged 4-<14 years were more sensitive to NO2 exposure at both low and high temperatures than the children aged < 1 year(P<0.05).The influence of relative humidity on respiratory outpatients among children was less than that of temperature.Compared with moderate humidity,low relative humidity was associated with an increase in the number of respiratory outpatient visits among children,while high relative humidity was associated with a decrease in the number of respiratory outpatient visits among children,but the effect was not statistically significant.Moreover,there was no significant difference in the effects of PM and gaseous pollutants at different humidity levels.Conclusions: High temperature was associated with a significant increase in respiratory outpatient visits among children,while the impact of different humidity levels had no significant difference.NO2,CO and O3 had an interactive association with the effect of temperature on the respiratory outpatients among children,while the impact of conventional air pollutants on the respiratory outpatients among children at different relative humidity levels had no significant difference. |
PDF Full Text Request