PM2.5 in Beijing – temporal pattern and its association with influenza
© Liang et al.; licensee BioMed Central Ltd. 2014
Received: 30 September 2014
Accepted: 30 November 2014
Published: 4 December 2014
Air pollution in Beijing, especially PM2.5, has received increasing attention in the past years. Despite Beijing being one of the most polluted cities in the world, there has still been a lack of quantitative research regarding the health impact of PM2.5 on the impact of diseases in Beijing. In this study, we aimed to characterize temporal pattern of PM2.5 and its potential association with human influenza in Beijing.
Based on the data collected on hourly ambient PM2.5 from year 2008 to 2013 and on monthly human influenza cases from 2008 and 2011, we investigated temporal patterns of PM2.5 over the five-year period and utilized the wavelet approach to exploring the potential association between PM2.5 and influenza.
Our results found that ambient PM2.5 pollution was severe in Beijing with PM2.5 concentrations being significantly higher than the standards of the World Health Organization, the US EPA, and the Chinese EPA in the majority of days during the study period. Furthermore, PM2.5 concentrations in the winter heating seasons were higher than those in non-heating seasons despite high variations. We also found significant association between ambient PM2.5 peak and human influenza case increase with a delayed effect (e.g. delayed effect of PM2.5 on influenza).
Ambient PM2.5 concentrations were significantly associated with human influenza cases in Beijing, which have important implications for public health and environmental actions.
KeywordsAir pollution PM2.5 Temporal pattern Association Influenza Beijing
Characteristics of PM 2.5 measurements and days exceeding the standards by the SEPA, EPA, and the WHO from 2008 to 2013
Range (lowest, highest)
PM2.5, particles with an aerodynamic diameter of less than 2.5 μm, has some important chemical and physical characteristics, varying from place to place . Many chemical constituents, such as sulfates, nitrates, ammonium, inorganic ions, organic elemental carbon, particle-bound water, polycyclic aromatic hydrocarbons (PAH), and among other, can be part of the composition of PM2.5. In Beijing, carbonaceous aerosols and major ions (sulfate, nitrate and ammonium) constituted more than 69% of PM2.5 with the major sources coming from dust, secondary sulfate and nitrate, coal combustion, and diesel and gasoline exhaust . Exposure to PM2.5 has already been linked to many health issues, such as arrhythmia , and systemic vascular dysfunction , among others. For the millions living and moving to Beijing, daily inhalation of polluted air could become a major health issue, with the government already advising citizens to stay inside on high concentration days . Therefore, the potential risk for increased mortality rates merits increased research in PM2.5 pollution itself, but despite PM2.5 pollution becoming a prevalent problem, the public, especially the ordinary residents in China lack of access to the quality and quantity of air quality data. Occasionally, the data come in small intervals, with one study only obtaining access to 37 days . Unfortunately, small sample sizes do not allow for thorough understanding of the problem at hand. Moreover, air pollution has become a long-term problem as well; many health effects are chronic due to long-term exposure. As such, it becomes important to analyze longer trends of air pollution in order to establish a clearer understanding of what the future might bring.
In addition to these health effects associated with PM2.5 exposure, there is increasing concern over its association with infectious diseases, some of which have caused major global health issues. Of particular note is influenza, which is a major global health problem, especially in China [17, 18]. Geographic variations in influenza in China are prevalent throughout the nation, creating complex problems regarding vaccination programs . Special strains of influenza outbreaks in China have presented challenges of adequately addressing influenza health crises . Influenza complications can lead to severe respiratory diseases, a health issue that has also been linked with PM2.5 exposure . Though ostensibly different health issues, exposure to PM2.5 can potentially exacerbate flu symptoms, yet no study has explored the relationship between PM2.5 exposure and influenza cases. To address this, we studied the measurements collected from Embassy of the United States in Beijing, ranging from 2008 to 2013, obtaining detailed information regarding PM2.5 concentrations on an hourly basis, and influenza case data from Beijing in an attempt to establish such a relationship, which may contribute to the future changes in environmental regulation and public health policies.
Materials and methods
Sources of data
Hourly measurements of PM2.5 from April 2008 to October 2013 were collected from an air quality monitoring site at the US Embassy in Beijing. The Embassy used two US EPA approved air quality monitors [MetOne BAM 1020] to measure PM2.5 particulates at hourly intervals in the Chaoyang district, where the Embassy compound is located (39.953°N 116.459°E). We chose the Embassy’s air pollution data because it recorded detailed measurements of PM2.5 over a long period of time, despite originating from only one source. Other sources of PM2.5 data include Chinese government agencies, but their released data are sporadic (short-term and discontinuous), limiting proper characterization of PM2.5. The hourly measurements (Chr) were converted to daily average and monthly average for subsequent analyses described below. From December 2008 to February 2009, the Embassy air quality monitor had malfunctions, leading to missing measurements for this three-month period. In addition to describing characteristics of PM2.5 concentrations over the five-year period, we were also interested in potential relationships between air quality and health impacts, specifically respiratory infections. In this study, we explored the association between PM2.5 concentrations and human influenza in urban area of Beijing. In China, influenza has been on the list of Class C notifiable diseases as part of China’s national infectious diseases surveillance (now called National Infectious Diseases Reporting Systems, or NIDR) since 1970 and individual cases were reported by hospitals and clinics required by law . At participating surveillance hospitals, each influenza-like case (defined as the one with body temperature ≥38°C and cough or sore throat) is recruited, sample (nasal or throat swab) is taken and sent for laboratory confirmation. Sample handling and processing follow national standard protocol by Ministry of Health . Both influenza-like case and confirmed case information are then reported to the NIDR system . Nevertheless, under-reporting does exist, as elaborated further in discussion section. In this study, reported influenza case data from January 2008 to December 2011 for all 17 districts in Beijing were retrieved from the National Infectious Disease Reporting system (NIDR). The reported cases from the NIDR system were aggregated for each district at the monthly interval. Since the US Embassy is located in Chaoyang district, reflecting a typical downtown setting of Beijing, we assume that the PM2.5 measurements from the US Embassy were likely representative of downtown environment. To explore the possible association between the PM2.5 and human influenza, we aggregated human influenza cases for the following eight districts which include and/or surround downtown areas: Haidian, Dongcheng, Xicheng, Chaoyang, Fengtai, Shijingshan, Chongwen, and Xuanwu districts. The aggregated data and PM2.5 measurements were then explored using the Wavelet analysis described below.
Descriptive and wavelet analyses
Descriptive statistical analyses were performed to characterize the following aspects of air quality in Beijing: daily and monthly averages, minimum and maximum concentrations of PM2.5, peak days/seasons of PM2.5, days of exceeding the standard for PM2.5 by the World Health Organization , the US EPA and the Chinese EPA ,, monthly variations in PM2.5 concentrations by overlaying the six years’ monthly averages.
Like many environmental and epidemiological time-series data, the PM2.5 and influenza time-series data are subject to non-stationary properties which are usually complex . To account for these factors, we used wavelet analysis to characterize the temporal patterns of monthly PM2.5 concentrations, following the general approach described by Cazelles et al. Wavelet analysis was used to decompose a time-series from a time domain to time-frequency (or time-period) domain and detect localized intermittent periods of a time-series . Following the general approach described by Grinsted et al. we used cross wavelet coherence approach to explore the possible association between the two time-series, PM2.5concentrations and human influenza cases. The cross wavelet angle was used to assess the phase difference between components of the two time series (for technical details, please refer to (Grinsted et al., 2004)). A Matlab package for performing cross wavelet coherence analysis was downloaded for the analysis (http://noc.ac.uk/using-science/crosswavelet-wavelet-coherence).
Many studies, in particular epidemiological studies, have demonstrated strong evidence for the association between particulate air pollution (from both PM10 and PM2.5) and human illness, in particular cardiovascular and respiratory disease. Both short- and long-term exposures to ambient particulate matters have implications for different health impacts [13, 27–31]. In China, much attention on air pollution has been focused on PM10, and the studies about PM2.5 exposure on health impact in China have just started. In this study, we report a five-year period of PM2.5 measurements from an urban site of Beijing and its possible association with human influenza. To our knowledge, this is the first study reporting comprehensive measurements of PM2.5 related to influenza in Beijing, China.
Although the present study only used data from one monitoring site in Beijing, it certainly reflects the unacceptably high air pollution occurring in one of the most populated cities in the world. From the monitoring records, on average, more than 81% of days each year, people live in the environment with polluted air exceeding US EPA and Chinese health standards. PM2.5 has increasingly been shown to be more harmful to human health than bigger particles since the smaller particles have more potential to be deposited in the alveoli and even penetrate the blood-gas barrier . However, China has only been recently releasing PM2.5 concentrations to the public in major cities. We all recognize that significant efforts have been made, but record-breaking pollution levels were recorded in the winter of 2013 in Beijing, China . This indicates that more comprehensive efforts still are needed so that the air quality improvements during the Beijing Olympic Games in 2008 could be sustainable [34, 35].
Air pollution has been implicated in respiratory illness infections . Moreover, many reports are related to indoor air pollution (e.g. combustion) which has been related to acute lower respiratory infections [37–40] and this has been a concern in many developing countries. There are not many studies related to ambient air pollution and infections, although there are reports on association between air pollution and pneumococcal disease related to respiratory viruses . In this study, we chose to explore the potential linkage between exposure to PM2.5 and human influenza, given the consideration of nature of the disease, biological plausibility, and availability of the influenza data. Using three-year’s data, our study suggested that human influenza cases were correlated to PM2.5 concentrations in Beijing and the finding is in general agreement with other studies . This seems to have a time lag while peaks of PM2.5 levels were followed by peaks of influenza in 2009 and 2010. Interestingly, the peak of PM2.5 levels were not obvious in 2008, so was relatively moderate for influenza cases during the same year, which further strengthens the correlation between PM2.5 exposure and influenza occurrence. The underlying possible mechanisms related to this are complex. There are some reports about ambient air pollution on respiratory infections in humans [43, 44] and it is likely that air pollution exposure causes host defense disorders, including both innate and cell-mediated immune responses against bacterial and viral infections [45, 46]. Various experimental studies have suggested that the deposition of particulates on epithelial cells that line the airways activates inflammatory signaling cascades [47, 48]. In addition, high PM2.5 levels could precipitate inflammatory and tissue remodeling changes in the lungs .
The study is also subject to some limitations. First, we only used one measurement source from the US Embassy, limiting spatial representativeness of the present work. Second, our data suffer from under-reporting of influenza cases; however, the under-reporting tends to occur in consistent pattern throughout the country and we believe that the relative pattern (e.g. seasonal variations in influenza) still holds. Third, the observational time periods of five years for PM2.5 levels and three years for influenza cases are relatively short, especially when a definite, strong correlation is concluded. Fourth, one kind of infectious disease, such as influenza in our study, may not be ideal, and more similar respiratory infectious diseases should be included in the future to demonstrate strong and broad correlation between PM2.5 and infectious diseases. Nevertheless, this study demonstrates a temporal correlation between PM2.5 pollution and influenza peak occurrence in Beijing, which provides significant impact on both environmental policy-making and public health preparedness.
In conclusion, despite the limitations, our study has indicated severity of PM2.5 pollution in urban Beijing and health implications associated with human influenza. Further studies are in urgent need to understand the mechanisms underlying the potential association as well as public health and environmental policy implications.
- PM2.5 :
Fine particulate matters
The United States of America
- US EPA:
United States Environmental Protection Agency.
We greatly appreciate The United States Embassy in Beijing for graciously providing PM2.5 concentration data and China NIDR System for influenza case data.
- Mehta S, Shin H, Burnett R, North T, Cohen AJ: Ambient particulate air pollution and acute lower respiratory infections: a systematic review and implications for estimating the global burden of disease. Air Qual Atmos Health. 2013, 6 (1): 69-83. 10.1007/s11869-011-0146-3.View ArticleGoogle Scholar
- Cohen AJ, Ross Anderson H, Ostro B, Pandey KD, Krzyzanowski M, Kunzli N, Gutschmidt K, Pope A, Romieu I, Samet JM, Smith K: The global burden of disease due to outdoor air pollution. J Toxic Environ Health A. 2005, 68 (13–14): 1301-1307.View ArticleGoogle Scholar
- Cohen AJ: Outdoor air pollution and lung cancer. Environ Health Perspect. 2000, 108 (Suppl 4): 743-750.View ArticleGoogle Scholar
- Cohen AJ, Pope CA: Lung cancer and air pollution. Environ Health Perspect. 1995, 103 (Suppl 8): 219-224. 10.1289/ehp.95103s8219.View ArticleGoogle Scholar
- Tuo Y, Li X, Wang JC: Negative effects of Beijing’s air pollution caused by urbanization on residents’ health. 2013, 2nd International Conference on Science and Social Research (ICSSR 2013). Atlantis Press, 732-735.http://www.atlantis-press.com/php/pub.php?publication=icssr-13&frame=http%3A//www.atlantis-press.com/php/paper-details.php%3Fid%3D7819,Google Scholar
- Cao JJ, Chow JC, Lee FSC, Watson JG: Evolution of PM2.5 measurements and standards in the US and future perspectives for China. Aerosol Air Qual Res. 2013, 13 (4): 1197-1211.Google Scholar
- Han LH, Zhuang GS, Cheng SY, Wang HY: Characteristics of re-suspended road dust and its significant effect on the airborne particulate pollution in Beijing. Huan Jing Ke Xue = Huanjing Kexue / [Bian Ji, Zhongguo Ke Xue Yuan Huan Jing Ke Xue Wei Yuan Hui "Huan Jing Ke Xue" Bian Ji Wei Yuan Hui]. 2009, 30 (1): 1-8.Google Scholar
- Liu Z, Hu B, Wang L, Wu F, Gao W, Wang Y: Seasonal and diurnal variation in particulate matter (PM and PM) at an urban site of Beijing: analyses from a 9-year study. Environ Sci Pollut Res Int. 2014, Epub ahead of printGoogle Scholar
- Zhang M, Song Y, Cai X: A health-based assessment of particulate air pollution in urban areas of Beijing in 2000-2004. Sci Total Environ. 2007, 376 (1–3): 100-108.View ArticleGoogle Scholar
- Gong P, Liang S, Carlton EJ, Jiang Q, Wu J, Wang L, Remais JV: Urbanisation and health in China. Lancet. 2012, 379 (9818): 843-852. 10.1016/S0140-6736(11)61878-3.View ArticleGoogle Scholar
- Schlesinger RB: The health impact of common inorganic components of fine particulate matter (PM2.5) in ambient air: a critical review. Inhal Toxicol. 2007, 19 (10): 811-832. 10.1080/08958370701402382.View ArticleGoogle Scholar
- WHO: Health effects of particulate matter: policy implications for countries in Eastern Europe, Caucasus and Central Asia. 2013, Denmark: Edited by Organization TWH, 20-Google Scholar
- Brunekreef B, Holgate ST: Air pollution and health. Lancet. 2002, 360 (9341): 1233-1242. 10.1016/S0140-6736(02)11274-8.View ArticleGoogle Scholar
- Kampfrath T, Maiseyeu A, Ying Z, Shah Z, Deiuliis JA, Xu X, Kherada N, Brook RD, Reddy KM, Padture NP, Parthasarathy S, Chen LC, Moffatt-Bruce S, Sun Q, Morawietz H, Rajagopalan S: Chronic fine particulate matter exposure induces systemic vascular dysfunction via NADPH oxidase and TLR4 pathways. Circ Res. 2011, 108 (6): 716-726. 10.1161/CIRCRESAHA.110.237560.View ArticleGoogle Scholar
- Contigency plans of severe air pollution of Beijing City. (2012) #34. 2013, China,http://www.bjmemc.com.cn/g327/s921/t1866.aspx,
- Zhang A, Qi Q, Jiang L, Zhou F, Wang J: Population exposure to PM2.5 in the urban area of Beijing. PLoS One. 2013, 8 (5): e63486-10.1371/journal.pone.0063486.View ArticleGoogle Scholar
- Jiang W, Liu S, Hou G, Li J, Zhuang Q, Wang S, Zhang P, Chen J: Chinese and global distribution of H9 subtype avian influenza viruses. PLoS One. 2012, 7 (12): e52671-10.1371/journal.pone.0052671.View ArticleGoogle Scholar
- Moscona A: Global transmission of oseltamivir-resistant influenza. N Engl J Med. 2009, 360 (10): 953-956. 10.1056/NEJMp0900648.View ArticleGoogle Scholar
- Yu H, Alonso WJ, Feng L, Tan Y, Shu Y, Yang W, Viboud C: Characterization of regional influenza seasonality patterns in China and implications for vaccination strategies: spatio-temporal modeling of surveillance data. PLoS Med. 2013, 10 (11): e1001552-10.1371/journal.pmed.1001552.View ArticleGoogle Scholar
- Wang L, Wang Y, Jin S, Wu Z, Chin DP, Koplan JP, Wilson ME: Emergence and control of infectious diseases in China. Lancet. 2008, 372 (9649): 1598-1605. 10.1016/S0140-6736(08)61365-3.View ArticleGoogle Scholar
- Qiu H, Yu IT, Tian L, Wang X, Tse LA, Tam W, Wong TW: Effects of coarse particulate matter on emergency hospital admissions for respiratory diseases: a time-series analysis in Hong Kong. Environ Health Perspect. 2012, 120 (4): 572-576. 10.1289/ehp.1104002.View ArticleGoogle Scholar
- MoH: Protocol for national influenza surveillance. 2010, Beijing: Ministry of HealthGoogle Scholar
- WHO: Health effects of particulate matter. 2013, The World Health Organization, 1-20.Google Scholar
- Cazelles B, Chavez M, Magny GC, Guegan JF, Hales S: Time-dependent spectral analysis of epidemiological time-series with wavelets. J R Soc Interface. 2007, 4 (15): 625-636. 10.1098/rsif.2007.0212.View ArticleGoogle Scholar
- Torrence C, Compo GP: A practical guide to wavelet analysis. Bull Am Meteorol Soc. 1998, 79 (1): 61-78. 10.1175/1520-0477(1998)079<0061:APGTWA>2.0.CO;2.View ArticleGoogle Scholar
- Grinsted A, Moore JC, Jevrejeva S: Application of the cross wavelet transform and wavelet coherence to geophysical time series. Nonlinear Process Geophys. 2004, 11 (5–6): 561-566.View ArticleGoogle Scholar
- Brunekreef B: Health effects of air pollution observed in cohort studies in Europe. J Expo Sci Environ Epidemiol. 2007, 17 (Suppl 2): S61-S65.View ArticleGoogle Scholar
- Brunekreef B: Air pollution and health–air quality standards. Verh K Acad Geneeskd Belg. 2011, 73 (5–6): 331-337.Google Scholar
- Roemer W, Hoek G, Brunekreef B: Effect of ambient winter air pollution on respiratory health of children with chronic respiratory symptoms. Am Rev Respir Dis. 1993, 147 (1): 118-124. 10.1164/ajrccm/147.1.118.View ArticleGoogle Scholar
- van der Zee S, Hoek G, Boezen HM, Schouten JP, van Wijnen JH, Brunekreef B: Acute effects of urban air pollution on respiratory health of children with and without chronic respiratory symptoms. Occup Environ Med. 1999, 56 (12): 802-812. 10.1136/oem.56.12.802.View ArticleGoogle Scholar
- van der Zee SC, Hoek G, Boezen MH, Schouten JP, van Wijnen JH, Brunekreef B: Acute effects of air pollution on respiratory health of 50-70 yr old adults. Eur Respir J. 2000, 15 (4): 700-709. 10.1034/j.1399-3003.2000.15d13.x.View ArticleGoogle Scholar
- Sun Q, Hong X, Wold LE: Cardiovascular effects of ambient particulate air pollution exposure. Circulation. 2010, 121 (25): 2755-2765. 10.1161/CIRCULATIONAHA.109.893461.View ArticleGoogle Scholar
- Steins R: China’s air pollution linked to millions of early deaths. 2013, National Public Radio online (http://www.npr.org/blogs/health/2013/04/02/176017887/chinas-air-pollution-linked-to-millions-of-early-deaths)Google Scholar
- Rich DQ, Kipen HM, Huang W, Wang GF, Wang YD, Zhu P, Ohman-Strickland P, Hu M, Philipp C, Diehl SR, Lu SE, Tong J, Gong J, Thomas D, Zhu T, Zhang JJ: Association between changes in air pollution levels during the Beijing olympics and biomarkers of inflammation and thrombosis in healthy young adults. Jama J Am Med Assoc. 2012, 307 (19): 2068-2078.View ArticleGoogle Scholar
- Xu X, Deng F, Guo X, Lv P, Zhong M, Liu C, Wang A, Tzan K, Jiang SY, Lippmann M, Rajagopalan S, Qu Q, Chen LC, Sun Q: Association of systemic inflammation with marked changes in particulate air pollution in Beijing in 2008. Toxicol Lett. 2012, 212 (2): 147-156. 10.1016/j.toxlet.2012.05.014.View ArticleGoogle Scholar
- Chauhan AJ, Johnston SL: Air pollution and infection in respiratory illness. Br Med Bull. 2003, 68: 95-112. 10.1093/bmb/ldg022.View ArticleGoogle Scholar
- Ezzati M, Kammen D: Indoor air pollution from biomass combustion and acute respiratory infections in Kenya: an exposure-response study. Lancet. 2001, 358 (9282): 619-624. 10.1016/S0140-6736(01)05777-4.View ArticleGoogle Scholar
- Pandey MR, Boleij JS, Smith KR, Wafula EM: Indoor air pollution in developing countries and acute respiratory infection in children. Lancet. 1989, 1 (8635): 427-429.View ArticleGoogle Scholar
- Smith KR: National burden of disease in India from indoor air pollution. Proc Natl Acad Sci U S A. 2000, 97 (24): 13286-13293. 10.1073/pnas.97.24.13286.View ArticleGoogle Scholar
- Smith KR, Samet JM, Romieu I, Bruce N: Indoor air pollution in developing countries and acute lower respiratory infections in children. Thorax. 2000, 55 (6): 518-532. 10.1136/thorax.55.6.518.View ArticleGoogle Scholar
- Kim PE, Musher DM, Glezen WP, Rodriguez-Barradas MC, Nahm WK, Wright CE: Association of invasive pneumococcal disease with season, atmospheric conditions, air pollution, and the isolation of respiratory viruses. Clin Infect Dis. 1996, 22 (1): 100-106. 10.1093/clinids/22.1.100.View ArticleGoogle Scholar
- Wong CM, Yang L, Thach TQ, Chau PY, Chan KP, Thomas GN, Lam TH, Wong TW, Hedley AJ, Peiris JS: Modification by influenza on health effects of air pollution in Hong Kong. Environ Health Perspect. 2009, 117 (2): 248-253. 10.1289/ehp.11605.View ArticleGoogle Scholar
- Arbex MA, Pereira LA, Carvalho-Oliveira R, Saldiva PH, Braga AL: The effect of air pollution on pneumonia-related emergency department visits in a region of extensive sugar cane plantations: a 30-month time-series study. J Epidemiol Community Health. 2014, 68 (7): 669-674. 10.1136/jech-2013-203709.View ArticleGoogle Scholar
- Brugha R, Grigg J: Urban air pollution and respiratory infections. Paediatr Respir Rev. 2014, 15 (2): 194-199.Google Scholar
- Xie Y, Zhang X, Tian Z, Jiang R, Chen R, Song W, Zhao J: Preexposure to PM2.5 exacerbates acute viral myocarditis associated with Th17 cell. Int J Cardiol. 2013, 168 (4): 3837-3845. 10.1016/j.ijcard.2013.06.025.View ArticleGoogle Scholar
- Yin XJ, Dong CC, Ma JY, Antonini JM, Roberts JR, Barger MW, Ma JK: Sustained effect of inhaled diesel exhaust particles on T-lymphocyte-mediated immune responses against Listeria monocytogenes. Toxicol Sci. 2005, 88 (1): 73-81. 10.1093/toxsci/kfi279.View ArticleGoogle Scholar
- Jin C, Shelburne CP, Li GJ, Potts EN, Riebe KJ, Sempowski GD, Foster WM, Abraham SN: Particulate allergens potentiate allergic asthma in mice through sustained IgE-mediated mast cell activation. J Clin Investig. 2011, 121 (3): 941-955. 10.1172/JCI43584.View ArticleGoogle Scholar
- Li N, Harkema JR, Lewandowski RP, Wang MY, Bramble LA, Gookin GR, Ning Z, Kleinman MT, Sioutas C, Nel AE: Ambient ultrafine particles provide a strong adjuvant effect in the secondary immune response: implication for traffic-related asthma flares. Am J Physiol Lung C. 2010, 299 (3): L374-L383. 10.1152/ajplung.00115.2010.View ArticleGoogle Scholar
- Pinkerton KE, Green FH, Saiki C, Vallyathan V, Plopper CG, Gopal V, Hung D, Bahne EB, Lin SS, Menache MG, Schenker MB: Distribution of particulate matter and tissue remodeling in the human lung. Environ Health Perspect. 2000, 108 (11): 1063-1069. 10.1289/ehp.001081063.View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.