深圳市大气PM10与呼吸系统疾病日门诊量的时间序列分析

目的探讨大气可吸入颗粒污染物（PM10）对医院呼吸系统疾病门诊量的影响。方法2012年1月1日至12月31日疾病资料来源于深圳市2家三级甲等综合性医院逐日门诊病例资料,空气污染物资料来自深圳市环境监测站,气象资料来自气象局。采用广义相加Poisson回归模型的时间序列分析,在控制长期趋势、星期几效应和气象等影响因素后,对大气PM10日均浓度与呼吸系统疾病日门诊量的关系和滞后效应进行分析。结果深圳市2012年全年日均大气PM10浓度为0．052mg／m^3,符合国家二级标准,2家医院全年呼吸系统门诊量为562174人次,平均1535．99人次／d。广义相加模型分析结果发现PM10日均浓度与呼吸系统疾病门诊量存在正相关关系。滞后6d时PM10日均浓度对呼吸系统疾病门诊量的影响最强[相对危险度（RR）为1．0047,95％CI：1．0036—1．0058]。引入CO、O3、NO2、SO2进行多污染物模型分析发现,多污染物模型的RR值相对单污染物模型有升有降（均P〈0．05）,其中以双污染物模型PM10＋SO2和三污染物模型PM10＋CO＋SO2中的PM10的RR值最高,分别为1．0059、1．0067。结论深圳市大气PM10污染与医院呼吸系统疾病日门诊量呈正相关关系,且存在滞后效应。     

Association of Respiratory Diseases Outpatient Visits and Air Pollution in a District, Guangzhou: a Time-series Study

目的 分析大气污染急性暴露对医院每日门诊人数的影响.方法 采用时间序列的半参数广义相加模型,在控制门诊人数的长期趋势、气象因素、星期几效应等混杂因素的基础上,分析广州市某区2009年1月1日—201l年12月31日大气污染与医院每日门诊人数的关系.结果 大气污染物PM10-2.5、PM2.5、NO2和SO2日平均浓度每增加10μ g/m3,医院呼吸系统疾病日门诊量的相对危险度分别为1.002 5(95％CI:0.998 9～1.018 2),1.003 5(95％CI:1.001 2～1.0164),1.0024 (95％CI:1.001 6～1.0056)和1.002 8(95％CI:0.977 8～1.0078).结论 广州市某区PM2.5和NO2日均浓度的短期升高可能会导致医院每日门诊人数的增加.     

长沙市大气污染物与脑卒中急诊关系的病例交叉研究

目的探讨长沙市大气污染物日均浓度与脑卒中急诊的相关性。方法收集2008—2009年中南大学湘雅三医院每日脑出血和脑梗死急诊数据,及长沙市同期大气二氧化硫(SO2)、二氧化氮(NO2)、可吸入颗粒物(PM10)和相关气象数据,采用季节分层的单向回顾性1∶4配对病例交叉设计建立单污染物和多污染物模型并进行分析。结果在调整气象因素(气温和相对湿度)的单污染物滞后模型中,秋季SO2、NO2、PM10日均浓度每增加10μg/m3,滞后0~3 d的脑出血与脑梗死OR值均大于1,且关联有统计学意义(P0.05)。多污染物模型中,控制PM10+NO2后秋季SO2浓度每增加10μg/m3时,脑梗死急诊的OR值(95%CI)为1.446(1.130~1.850);控制PM10+SO2后秋季NO2浓度每增加10μg/m3时,脑出血急诊的OR值(95%CI)为1.615(1.131~2.305);控制其他污染物后冬季NO2、PM10浓度每增加10μg/m3,脑出血急诊的OR值(95%CI)分别为1.325(1.019~1.724)和1.117(1.024~1.218),关联均有统计学意义(P0.05)。结论长沙市秋季SO2、NO2、PM10浓度与脑出血和脑梗死急诊均呈正向关联,其中SO2对脑梗死急诊影响更明显,NO2对脑出血急诊影响更明显;冬季NO2、PM10浓度与脑出血急诊亦呈正向关联。     

上海市闵行区大气污染与居民日死亡关系的时间序列研究

[目的]分析大气污染对居民每日死亡的急性效应。[方法]采用时间序列的广义相加模型(GAM),在控制了时间的长期趋势、季节趋势、周效应、气象因素等混杂因素的基础上,研究上海市闵行区2001年1月1日~2004年12月31日大气污染与居民日死亡的关系。[结果]大气中可吸入颗粒物(PM10)、二氧化硫(SO2)以及二氧化氮(NO2)的日均浓度每增加10μg/m3,对应居民死亡相对危险度分别为1.0030(95%CI:1.0005~1.0055)、1.0123(95%CI:1.0051~1.0195)和1.0126(95%CI:1.0059~1.0194)。[结论]上海市闵行区大气污染物PM10、NO2、SO2的浓度变化对居民日死亡人数有影响。     

上海市气温变化对医院急诊人次的影响

目的 研究上海市日均气温与三级医院医保急诊人次的关系.方法 应用广义相加模型分析时间序列资料,并在模型中加入自回归模型AR(P)处理时间序列资料自相关的问题,在控制了与时间有关的中长期趋势、星期效应、节假日效应、SARS事件、大气污染等混杂因素的基础上,拟合二次函数结合导数原理分析上海市2002-2004年间日均气温与三级医院医保急诊人次的关系.结果 当气温低于14.71℃时,气温每升高1℃对应急诊人次增加艘值的95%C/均小于1;当气温高于19.59℃时,气温每升高1℃对应急诊人次增加RR值的95%CI均大于1;而在温度段为14.71～19.59%,气温每升高1℃对应急诊人次增加RR值的95%CI包含1,称之为"最适温度段".结论 目前上海市日均气温偏离最适温度段时,气温变化对三级医院医保急诊人次有影响.     

广州地区空气污染对儿童呼吸系统疾病就诊人次的影响研究

目的探讨广州地区主要的大气污染物(NO2、PM10和SO2)与儿童呼吸系统疾病门诊人次的关系。方法通过广州市环境保护局和广州某医院分别获得2005年1月1日—2011年12月31日大气污染物(NO2、PM10、SO2)的日均浓度资料和儿科呼吸系统疾病日门诊人次资料,采用分布滞后线性模型分析大气NO2、PM10、SO2对儿科呼吸系统疾病门诊人次的影响。结果大气NO2、PM10和SO2浓度对儿科呼吸系统疾病门诊人次的滞后效应可持续至15 d。大气NO2、PM10、SO2浓度每升高10μg/m3对儿科呼吸系统疾病门诊人次影响的累积效应在0~30 d时均有统计学意义(P0.05),且均于15 d达到最大值(NO2:RR=1.029 2,95%CI:1.024 6~1.033 8;PM10:RR=1.020 4,95%CI:1.016 4~1.024 5;SO2:RR=1.040 8,95%CI:1.032 5~1.049 1)。结论广州大气NO2、PM10、SO2浓度的升高可能会造成15 d内儿童呼吸系统疾病门诊就诊人次的增加。     

2002-2005年上海市两监测点大气污染物变化规律

为了解上海市两监测点大气污染物SO2、NO2和PM10的时空变化规律。研究人员收集2002-2005年上海市A、B两环境监测点（A监测点位于市区，B监测点位于郊区）SO2、NO2和PM10的日均浓度。     

大气污染对变应性疾病及花粉症就诊人次的影响

目的 研究大气污染物浓度对医院变应性疾病和花粉症日就诊人次的影响.方法 收集2004年4-9月北京市8个国家监测点大气污染物[SO2、NO2、可吸入颗粒物(PM10)]浓度、4个观测点花粉日监测数据、气象资料及北京世纪坛医院变态反应科同时段变应性疾病和花粉症日就诊人次资料,应用时间序列分析的广义相加泊松回归模型进行定量分析,并考虑滞后效应和多种空气污染物的影响.结果 研究期间大气SO2、NO2、PM10日均浓度分别为(20.9±12.9)、(58.6±13.6)、(126.8 ±64.1)μg/m3,花粉日均浓度为(163.8±209.0)粒/1000 mm2,变应性疾病日就诊(16.3±5.3)人次,花粉症日就诊(3.5±5.0)人次.时间序列分析显示,花粉浓度每升高100粒/1000 mm2,第2天的变应性疾病日就诊人次增加2.44%(95%CI:0.75%～4.13%),当天的花粉症日就诊人次增加6.58%(95%CI:3.82%～9.34%).而大气污染物(NO2、SO2和PM10)对变应性疾病和花粉症日就诊人次的影响呈现明显的滞后效应:NO2每升高10 μg/m3,滞后6 d的变应性疾病日就诊人次增加3.14%(95%CI:0.42%～5.85%);S02滞后1 d、NO2滞后6 d、PM10滞后3 d对花粉症日就诊人次影响较大,但差异均无统计学意义[RR值(95%CI值)分别为1.0460(0.9640～1.1280)、1.0325(0.9633～1.1017)、1.0079(0.9942～1.0217)].将4种大气污染物同时引入模型分析时,其效应稍微增强:花粉浓度每升高100粒/1000 mm2,变应性疾病日就诊人次增加2.56%(95%CI:0.80%～4.31%),花粉症日就诊人次增加6.81%(95%CI:3.91%～9.71%).结论 影响变应性疾病和花粉症日就诊人次的环境因素主要为空气花粉浓度,大气污染物的作用不大.     

气象因素与心脑血管疾病急诊人次的时间序列分析

目的 探讨日均气温、相对湿度和风速与医院日心脑血管疾病急诊就诊人次的相关性.方法 收集北京市某三级甲等医院日心脑血管疾病急诊就诊人次和该地区日均气温、相对湿度和风速的时间序列数据.收集北京市该城区PM10、SO2和NO2日均浓度的时间序列数据.利用立方平滑样条函数将日均气温、相对湿度和风速以及作为潜在混杂因素的PM10、SO2和NO2日均浓度引入,同医院日心脑血管疾病急诊就诊人次间建立Poisson广义相加模型.根据AIC最小的原则,选择最终进入模型的变量,并确定其立方平滑样条函数自由度取值.结果 医院日心脑血管疾病急诊就诊人次与日均气温和相对湿度表现出一定的非线性相关趋势,但无统计学意义(P>0.1);与日均风速表现出负相关趋势,但无统计学意义(P>0.1).结论 北京市某城区气温、相对湿度和风速与医院心脑血管疾病急诊人次的相关性不明显.     

天津市空气污染物对脑卒中死亡影响的时间序列分析

目的 探讨天津市大气污染对居民脑卒中死亡率的影响,为脑卒中的预防控制提供依据.方法 采用天津市疾病预防控制中心收集的居民全死因监测数据,气象资料和大气污染资料来源于天津市气象局和天津市环境监测中心.采用时间序列的泊松回归广义可加模型进行天津市每日大气污染与居民脑卒中死亡危险度分析,同时控制气象因素、长期趋势、星期几效应以及人口数等混杂因素的影响,进行单污染物和多污染物分析.结果 2001至2009年天津市脑卒中粗死亡率为136.67～160.01/10万,有逐年上升趋势(P=0.000),但天津市脑卒中世界标化死亡率为138.36～99.14/10万,呈逐年下降趋势(P=0.000);大气中SO2、NO2、PM10日均浓度每升高10μg/m3,脑卒中死亡的风险RR值分别为1.0105(95％CI:1.0060～1.0153),1.0197(95％CI:1.0149～1.0246)和1.0064(95％CI:1.0052～1.0077).SO2效应在1日后达到最大,NO2、PM10效应在当日达到最大.结论 天津市大气污染能增加人群脑卒中死亡风险,可能对脑卒中急性发作起到诱导作用.     

上海市气温变化对医院儿科日门诊人次的影响

目的研究上海市气温变化与医院儿科日门诊人次的关系。方法选用广义相加模型分析时间序列资料,在控制与时间有关的中长期趋势、星期效应、气象因素等混杂因素的基础上,分析上海市2001-2009年日均气温变化与儿科门诊人次的关系。结果当气温小于15℃时,每升高1℃,儿科门诊就诊的相对危险度为1．0235,95％CI为1．0252～1．0218;当气温在15％和20℃之间时,每升高1℃,儿科门诊就诊的相对危险度为0．9951,95％CI为：0．9972～0．9929;当气温大于20％时,每升高1℃,儿科门诊就诊的相对危险度为1．0345,95％CI为1．0368～1．0323。结论上海市日均气温对医院儿科门诊人次有影响。     

Association between hospital emergency visits for asthma and air pollution in Valencia,Spain

OBJECTIVE: To assess the short term effect of concentrations of black smoke, sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) in ambient air on emergency room visits for asthma in the city of Valencia, Spain during the period 1994-5. METHODS: Ecological study with time series data and application of Poisson regression. Associations between number of daily emergency visits in a city''s hospital and concentrations of air pollutants were analysed taking into account potential confounding factors by the standardised protocol of the air pollution and health: a European approach (APHEA) project. RESULTS: Mean (range) daily number of emergency room visits for asthma was 1 (0-5). Concentrations of all pollutants studied remained within current air quality standards. The association between an increase of 10 micrograms/m3 in ambient air pollution and asthma, measured as a relative risk (RR) of emergency visits, was significant for NO2 24 hour mean (lag 0, RR 1.076, 95% confidence interval (95% CI) 1.020 to 1.134), NO2 hour maximum (lag 0, RR 1.037, 95% CI 1.008 to 1.066), and O3 hour maximum (lag 1, RR 1.063, CI 95% 1.014 to 1.114). The association was not significant for SO2 or for black smoke during the period analysed. The effects were not significantly different for the time of year, cold months (November to April), or warm months (May to October). CONCLUSIONS: Current concentrations of ambient air pollution in Valencia are significantly associated with emergency room visits for asthma. This association is high and more consistent for NO2 and O3 than for particulate matter and SO2 (classic pollutants).       

上海市大气污染与某医院呼吸系统疾病门诊量关系的时间序列研究

[目的]探讨上海市大气污染物对人群呼吸系统疾病门诊量的短期影响。[方法]收集2010年1月1日—2012年10月31日上海市某三级甲等医院呼吸系统疾病每日门诊量统计资料和同期上海市大气及气象监测资料,采用时间序列的半参数广义相加模型,在控制了长期趋势、星期几效应、假期效应及气象因素等混杂因素的基础上,分析大气污染物与呼吸系统疾病日门诊量的关系。[结果]研究期间,呼吸系统疾病日门诊量为76~382人次。单污染模型中,二氧化硫（SO2）滞后4 d对呼吸系统疾病的影响最明显,二氧化氮（NO2）、可吸入颗粒物（PM10）滞后6 d的影响最明显;SO2、NO2、PM10浓度每增加10μg/m3,呼吸系统疾病日门诊量上升0.69%（RR=1.006 9,95%CI：1.003 5~1.010 3）、0.54%（RR=1.005 4,95%CI：1.002 8~1.007 9）和0.20%（RR=1.002 0,95%CI：1.001 1~1.002 8）。多污染模型中,调整其他污染物后,所有污染物健康效应估计值均较单污染模型降低,并不改变各污染物浓度与呼吸系统疾病日门诊量的正相关关系。[结论]大气污染物SO2、NO2、PM10与人群呼吸系统疾病门诊量存在正相关。     

1,3-丁二烯作业工人的DNA修复能力

[目的]探讨DNA修复能力与1,3-丁二烯（BD）职业暴露致外周血淋巴细胞遗传学损伤的关联性。[方法]收集个人职业史、年龄、性别、吸烟和饮酒状况等信息,气相色谱法检测作业环境的BD浓度,利用染色体断裂试验评价60名职业BD暴露工人和60名非暴露工人的外周血淋巴细胞对诱变剂博莱霉素所致DNA损伤的修复能力。[结果]作业区空气中BD浓度为1.8（0.59~2.76）mg/m3。职业BD暴露组染色体断裂率[（1.06±0.41）%]高于对照组[（0.85±0.36）%,P〈0.01]。职业BD暴露人群中饮酒者的b/c值高于不饮酒者（P〈0.05）。[结论]DNA修复能力的下降可能是BD致癌过程中的重要生物学事件。     

大气SO2暴露与医院每日急诊和门诊人次关系的多中心时间序列研究

  目的  分析大气二氧化硫(sulfur dioxide, SO₂)暴露对北京、西安、武汉和广州市等地医院每日急诊和门诊人次的影响。  方法  收集2013年1月1日至2015年12月31日上述城市5家医院的急诊和门诊资料、大气污染物资料和气象资料。采用广义相加模型分析SO₂浓度与医院每日急诊和门诊人次的关系,采用Meta随机效应模型分析得到合并效应值。  结果  纳入总急诊和门诊人次分别为411 277和4 935 282人次。北京、西安、武汉和广州市等地的SO₂年平均浓度分别为16.5、30.1、30.5和15.0 μg/m3。SO₂对急诊和门诊的影响存在滞后效应,单日滞后效应逐日递减,且在滞后3 d失去统计学意义。滞后0~2 d影响最大,SO₂平均浓度每升高10 μg/m3,每日急诊和门诊分别增加3.44%(95% CI:1.65%~5.26%)和1.32%(95% CI:0.45%~2.20%)。SO₂对每日急诊和门诊影响的暴露-反应关系曲线均呈近似线性,但在高浓度段有变平缓的趋势。此外,SO₂引起的急诊和门诊人群归因分值分别为6.80%(95% CI:2.20%~11.10%)和2.84%(95% CI:0.98%~4.64%)。  结论  中国城市SO₂短期暴露可增加医院急诊和门诊的就诊风险,应加强SO₂污染防治并修订相应标准。     

Association between air pollution and ischemic cardiovascular emergency room visits

This study observed the relationship between air pollutants and ischemic cardiac diseases such as angina and acute myocardial infarction in a representative cardiovascular center emergency room in São Paulo, Brazil. Daily emergency room admissions to the Institute of the Heart of the University of São Paulo, as well as data concerning daily air pollutant levels and meteorological variables, were collected from January 1994 to August 1995. Generalized additive Poisson regressions were fitted to the logarithm of the expected values of total emergency room visits due to angina or acute myocardial infarction, controlling for smooth functions of season and weather and indicators for days of the week. All investigated pollutants were positively associated with ischemic cardiovascular disease emergency room visits, and the time lags were relatively short, but only CO presented an effect that was statistically significant. An interquartile range increase in CO was associated with an increase of 6.4% (95% CI: 0.7-12.1) in daily angina or acute myocardial infarction emergency room visits. This result did not change when estimates were done using linear models and natural cubic splines. This study showed that air pollution has a role in cardiovascular morbidity in São Paulo, reinforcing the necessity for air pollutant emission-controlling polices in urban areas.     

Air pollution and emergency room visits for asthma in Santa Clara County, California.

During the winters of 1986-1987 through 1991-1992, rainfall throughout much of Northern California was subnormal, resulting in intermittent accumulation of air pollution, much of which was attributable to residential wood combustion (RWC). This investigation examined whether there was a relationship between ambient air pollution in Santa Clara County, California and emergency room visits for asthma during the winters of 1988-1989 through 1991-1992. Emergency room (ER) records from three acute-care hospitals were abstracted to compile daily visits for asthma and a control diagnosis (gastroenteritis) for 3-month periods during each winter. Air monitoring data included daily coefficient of haze (COH) and every-other-day particulate matter with aerodynamic diameter equal to or less than 10 microns (PM10, 24-hr average), as well as hourly nitrogen dioxide and ozone concentrations. Daily COH measurements were used to predict values for missing days of PM10 to develop a complete PM10 time series. Daily data were also obtained for temperature, precipitation, and relative humidity. In time-series analyses using Poisson regression, consistent relationships were found between ER visits for asthma and PM10. Same-day nitrogen dioxide concentrations were also associated with asthma ER visits, while ozone was not. Because there was a significant interaction between PM10 and minimum temperature in this data set, estimates of relative risks (RRs) for PM10-associated asthma ER visits were temperature-dependent. A 60 micrograms/m3 change in PM10 (2-day lag) corresponded to RRs of 1.43 (95% CI = 1.18-1.69) at 20 degrees F, representing the low end of the temperature distribution, 1.27 (95% CI = 1.13-1.42) at 30 degrees F, and 1.11 (95% CI = 1.03-1.19) at 41 degrees F, the mean of the observed minimum temperature. ER visits for gastroenteritis were not significantly associated with any pollutant variable. Several sensitivity analyses, including the use of robust regressions and of nonparametric methods for fitting time trends and temperature effects in the data, supported these findings. These results demonstrate an association between ambient wintertime PM10 and exacerbations of asthma in an area where one of the principal sources of PM10 is RWC.     

2004-2006年北京夏季最低气温对心脑血管疾病急诊数的影响

目的 探讨北京市夏季最低气温对心脑血管疾病(ICD10:100～199)急诊的影响.方法 收集2004-2006年北京大学某医院急诊科心脑血管疾病急诊资料、北京市环境监测中心大气污染物数据和中国气象科学数据共享服务网的气象资料,应用时间分层的病例交叉设计研究方法进行数据分析.结果 在控制大气污染物SO_2、NO_2、可吸入颗粒物(PM10)影响的情况下,无滞后夏季最低气温对心脑血管疾病总急诊、冠心病急诊、心律失常急诊、心衰急诊和脑血管疾病急诊的影响最大,气温每升高1℃,OR值分别为1.039(95%CI:1.008～1.071),1.077(95%CI:0.987～1.174),1.037(95%CI:0.963～1.116).1.103(95%CI:0.909～1.339)和 1.030(95%CI:0.985～1.077),其中最低气温与总心脑血管疾病急诊的关联有统计学意义(P<0.05).在多因素模型中,考虑到相对湿度因素时,气温每升高1℃对冠心病急诊和脑血管病急诊的OR值分别为1.095(95%CI:1.001～1.075)和1.050(95%CI:1.002～1.100),关联具有统计学意义(P<0.05).结论 夏季最低气温升高可以导致心脑血管疾病总急诊增加,同时相对湿度可能与气温有协同作用,可导致冠心病急诊,脑血管病急诊增加.

Abstract：

Objective To explore the association between the minimum temperature in different seasons and the hospital emergency room visits for cardiocerebrovascular diseases(International Classification of Diseases,tenth vision ICD-10：100-199)in Beijing.China.Methods The data of the daily hospital emergency room visits for cardiocerebrevascular diseases(ICD-10：100-199)from one of Peking university hospitals,the data of relevant ambient air pollution from the Beijing Municipal Environmental Monitoring Center and the data of meteorological index from China meteorological data sharing service system between 2004—2006 were collected The time-stratified case-crossover design was used to analyze the data.Results After adjusting SO_2,NO_2,and PM10.The results showed that each 1℃ increase in the daily minimum temperature in summer was associated with the intraday hospital emergency room visits(OR=1.039,P<0.05)for the total cardiocerebrovascular diseases.In multi-factor model,considering relative humidity,1℃ increase in the daily minimum temperature was associated with the coronary heart disease(OR=1.095,95％CI:1.001—1.075)and the cerebrovascular diseases(OR=1.050,95％CI：1.002—1.100)(P<0.05).Conclusion These outcomes suggest that elevated level of minimum temperature in summer will increase the hospital emergency room visits for the total circulatory diseases,and the relative humidity may enhance the effects of minimum temperature on the hospital emergency room visits of coronary heart disease and cerebrovaseular diseases.     

Association between maternal exposure to ambient air pollutants during pregnancy and fetal growth restriction

Previous research demonstrated consistent associations between ambient air pollution and emergency room visits, hospitalizations, and mortality. Effect of air pollution on perinatal outcomes has recently drawn more attention. We examined the association between intrauterine growth restriction (IUGR) among singleton term live births and sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), ozone (O3), and fine particles (PM2.5) present in ambient air in the Canadian cities of Calgary, Edmonton, and Montreal for the period 1985-2000. Multiple logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for IUGR, based on average daily levels of individual pollutants over each month and trimester of pregnancy after adjustment for maternal age, parity, infant gender, season, and city of residence. A 1 ppm increase in CO was associated with an increased risk of IUGR in the first (OR=1.18; 95% CI 1.14-1.23), second (OR=1.15; 95% CI 1.10-1.19) and third (OR=1.19; 95% CI 1.14-1.24) trimesters of pregnancy, respectively. A 20 ppb increase in NO2 (OR=1.16; 95% CI 1.09-1.24; OR=1.14; 95% CI 1.06--1.21; and OR=1.16; 95% CI 1.09-1.24 in the first, second, and third trimesters) and a 10 mug/m3 increase in PM2.5 (OR=1.07; 95% CI 1.03-1.10; OR=1.06; 95% CI 1.03-1.10; and OR=1.06; 95% CI 1.03-1.10) were also associated with an increased risk of IUGR. Consistent results were found when ORs were calculated by month rather than trimester of pregnancy. Our findings add to the emerging body of evidence that exposure to relatively low levels of ambient air pollutants in urban areas during pregnancy is associated with adverse effects on fetal growth.