Table 1 Descriptive information for all included studies, categorized by the combination of risk factor exposures
Study | Type | Location | Duration | Outcome | Population | Pollutants Measured | Pollen Measured | Temperature Measurement |
|---|---|---|---|---|---|---|---|---|
Air pollution, heat, and pollen (n = 6) | ||||||||
 Respiratory | ||||||||
  Hebbern 2015 [47] | Time series | 10 Canadian cities | Apr 1994- Mar 2007 | Asthma hospital admissions | Not reported | CO, O3, NO2, SO2, PM10, PM2.5 | Weed, tree, grass | Daily Mean |
  Makra 2015 [48] | Time series | Szeged, Hungary | 1999–2007 | Asthma emergency room visits | 0–14 years; 15–64 years; 65+ years (n = 936 asthma ER visits) | CO, NO, NO2, SO2, O3, PM10 | Ambrosia, maple, alder, mugwort, birch, hemp, hornbeam, goosefoot, hazel, ash, walnut, mulberry, pine, plantain, platan, grasses, poplar, oak, dock, willow, yew, linden, elm, nettle | Daily Mean, daily maximum, daily minimum, daily range |
  Matyasovszky 2011 [49] | Time series | Szeged, Hungary | 1999–2007 | Respiratory hospital admissions | All ages; 15–64 years; 65+ years (n = 133,464 hospital admission) | CO, NO, NO2, SO2, O3, PM10 | Ambrosia, maple, alder, mugwort, birch, hemp, hornbeam, goosefoot, hazel, ash, walnut, mulberry, pine, plantain, platan, grasses, poplar, oak, dock, willow, yew, linden, elm, nettle | Daily mean, maximum, minimum, range |
  Mazenq 2017 [50] | Nested case control | Southeastern France | Jan 2013-Dec 2013 | Asthma emergency room visits | 3–18 years (n = 1182 asthma ER visits) | PM10, PM2.5 | cypress, birch, ash, grass, urticaceae | Daily average |
  Mireku 2009 [51] | Retrospective time series | Detroit, MI | Jan 2004- Dec 2005 | Asthma emergency room visits | 1–18 years (n = 25,401 asthma ER visits) | PM2.5, PM10, SO2, O3 | Total | Daily average |
  Witonsky 2019 [52] | Retrospective cohort | Bronx, NY | Jan 2001- Dec 2008 | Asthma emergency room visits and hospitalizations | All ages (n = 42,065 asthma ER visits; n = 1664 asthma-related hospitalizations) | NOx, O3, SO2 | Grass, weed, tree, | Daily average |
Air pollution and temperature (n = 39) | ||||||||
 Multiple health endpoints | ||||||||
  Analitis 2014 [53] | Ecological time series | 9 European cities | 1990–2004 | All natural, cardiovascular, and respiratory mortality | 0–64, 65–74, 75–84, and 85+ years (n not reported) | SO2, PM10, NO2, O3, CO |  | 3-h average |
  Analitis 2018 [54] | Ecological time series | 9 European cities | 2004–2010 | All natural, cardiovascular, and respiratory mortality | All ages; 15–64, 65–74, 75+ years (n not reported) | PM10, O3, NO2 |  | Daily mean |
  Breitner 2014 [55] | Time series | Bavaria, Germany | 1990–2006 | Non accidental, cardiovascular, respiratory mortality | < 85, 85+ years (n = 338,631 deaths) | PM10, O3 |  | Daily mean |
  Cheng 2012 [56] | Time series | Shanghai, China | 2001–2004 | Non-accidental, cardiovascular, respiratory mortality | All ages (n = 173,911 deaths) | PM10, O3, SO2, NO2 |  | Daily minimum, maximum, mean |
  Li 2011 [57] | Time Series | Tianjin, China | 2007–2009 | Cardiovascular, respiratory, cardiopulmonary, stroke and IDH, Non accidental mortality | All ages; < 65, 65+ years (n = 111,087 deaths) | PM10, SO2, NO2 |  | Daily mean |
  Li 2015 [58] | Time Series | Guangzhou, China | 2003–2011 | Non accidental mortality, cardiovascular mortality, respiratory mortality | < 65, 65+ years (n = 213,737 deaths) | PM10 |  | Daily mean |
  Lokys 2018 [59] | Time series | 28 districts, Germany | 2001–2011 | Cardiovascular and respiratory hospital admissions | Not reported | NO2, SO2, O3, PM10 |  | Daily mean |
 All-cause or non-accidental only | ||||||||
  Burkart 2013 [60] | Time Series | Berlin and Lisbon | 1998–2010 | All cause mortality | Age not reported (n = 698,586 deaths) | PM10, O3 |  | Hourly mean |
  Chen 2018a [61] | Time series | 8 European cities | 1999–2013 | Non accidental mortality | 0–74, 75+ years (n = 742,526 deaths) | PM2.5, PM10, O3 |  | Daily mean |
  Chen 2018b [62] | Time Series | 8 European cities; 86 US Cities | 1999–2013; 1987–2000 | Non accidental mortality | All ages (n not reported) | PM10, NO2, O3 |  | Daily mean |
  Dear 2005 [63] | Time series | 12 French cities | Aug-03 | All cause mortality | All ages (n not reported) | O3 |  | 24 h Minimum, maximum |
  Filleul 2006 [64] | Time series | 9 French cities | Aug-03 | All cause mortality | All ages (n not reported) | O3 |  | Daily maximum |
  Jhun 2014 [65] | Time series | 97 cities | 1987–2000 | Non accidental mortality | 0–99 years (n not reported) | O3 |  | Daily high |
  Kim 2015 [66] | Time series | 7 South Korean cities | Jan 2000-Dec 2009 | Daily non accidental deaths | < 65, 65+ years (n = 828,787 deaths) | PM10 |  | Daily mean |
  Liu 2016 [67] | Time Series | 20 US communities | 1987–2000 | Non accidental mortality | Not reported | O3 |  | Daily mean |
  Meng 2012 [68] | Time series | 8 Chinese cities | 2001–2008 | Non accidental mortality | Not reported | PM10 |  | Daily mean |
  Moolgavkar 2003 [69] | Time Series | Cook County, IL & LA County, CA | 1987–1995 | Non accidental mortality | All ages; 65+ years (n not reported) | O3, SO2, NO2, CO, PM |  | Daily minimum, median, maximum |
  Park 2011 [70] | Time series | Seoul, South Korea | Jun 1999- Dec 2007 | Non accidental mortality | All ages; 65–74, 75–84, 85+ years (n = 291,665 deaths) | PM10, NO2, SO2, CO, O3 |  | Daily mean, minimum, maximum |
  Pattenden 2010 [71] | Time series | 15 conurbations in England and Wales | 1993–2003 | All cause mortality | 0–64, 65–74, 75–84, 85+ years (n not reported) | O3, PM10 |  | Two day Mean |
  Peng 2013 [72] | Time series | 23 European Cities; 12 Canadian Cities; 86 US cities | Canada 1987–1996; Europe 1990–1997; US 1987–1996 | Non accidental mortality | All ages; < 75, 75+ years (n not reported) | NO2, SO2, O3, PM10 |  | Daily mean |
  Rainham 2005 [73] | Time series | Toronto, Canada | 1981–1999 | Non Trauma mortality | Not reported | CO, NO2, SO2, O3, PM2.5 |  | Daily mean |
Scortichini 2018 [74] | Time series | 25 Italian cities | 2006–2010 | Mortality from natural causes | 35+ years (n = 187,743 deaths) | O3, PM10 |  | Daily mean |
  Shaposhnikov 2014 [75] | Time series | Moscow, Russia | 2006–2009, 2010 | Non accidental mortality | All ages; < 65, 65+ years (n = 10,860 deaths) | O3, PM10 |  | Daily mean |
  Stafoggia 2008 [76] | Case crossover | 9 Italian cities | 1997–2004 | Mortality from natural causes | 35+ years (n = 321,024 deaths) | PM10 |  | Daily mean, apparent |
  Sun 2015 [77] | Time Series | Hong Kong | 1999–2011 | Mortality from natural causes | Age not reported (n = 456,317 deaths) | PM2.5, NO2, SO2, O3 |  | Daily mean |
  Vanos 2015 [78] | Time series | 12 Canadian cities | 1981–2008 | Non accidental mortality | Not reported | O3, NO2, PM2.5, SO2 |  | Daily mean |
  Wilson 2014 [79] | Time Series | 95 US cities | 1987–2000 | Mortality | Not reported | O3 |  | Daily mean |
  Zhang 2006 [80] | Time series | Shanghai, China | Jan 2001- Dec 2004 | Non accidental mortality | All ages; 0–4, 5–44, 45–64, 65+ years (n = 173,911 deaths) | O3, PM10, SO2, NO2 |  | Daily mean |
 Respiratory only | ||||||||
  Ding 2017 [81] | Case crossover | Taiwan | 2000–2013 | COPD mortality | 40–64, 65–79, 80+ years (n not reported) | PM2.5, O3, SO2 |  | Daily mean, maximum, minimum |
  Jo 2017 [82] | Time series | Busan, South Korea | 2007–2010 | Hospital admissions for respiratory disease | 0–15,16–64, 65+ years (n not reported) | PM2.5, PM10 |  | Daily average, minimum, maximum, range |
  Kunikullaya 2017 [83] | Retrospective ecological time series | Bangalore, India | One year | Asthma-related emergency room visits and hospitalizations | > 18 years (n not reported) | SO2, NO2, PM10, PM2.5 |  | Daily mean |
  Lam 2016 [84] | Time series | Hong Kong | 2004–2011 | Asthma hospitalizations | < 5, 5–14, 15–59, 60+ years (n = 56,112 asthma admission) | PM10, SO2, NO2, O3 |  | Daily mean |
  Mirabelli 2016 [85] | Retrospective cross sectional | United States | 2006–2010 | Asthma symptoms | 18+ years (n = 50,356 respondents) | PM2.5, O3 |  | Average daily mean |
  Qiu 2018 [86] | Time series | Chengdu, China | Jan 2015- Dec 2016 | COPD hospital admissions | All ages; < 60, 60–70, 70–80, 80+ years (n = 54,966 COPD admission) | PM10, PM2.5, NO2, SO2, CO, O3 |  | Daily mean |
  Winquist 2014 [87] | Time Series | Atlanta, GA | 16 years | Asthma emergency department visits | 5–17 years (n not reported) | CO, NO2, SO2, O3, PM2.5 |  | Daily minimum, maximum, |
 Cardiovascular only | ||||||||
  Lee 2018 [88] | Case crossover | Seoul, South Korea | 2008–2014 | Migraine emergency room visits | All ages; < 40, 40–64, 65+ years (n = 18,921 ER visits) | PM2.5, PM10, NO2, SO2, O3, CO |  | Hourly mean |
  Luo 2017 [89] | Time series | 3 Chinese cities | 2008–2011 | Cardiovascular mortality | All ages; < 65, 65+ years (n = 290,593 deaths) | PM10, NO2, SO2 |  | Daily minimum, maximum, mean |
  Ren 2008 [90] | Time Series | 95 US cities | 1987–2000 | Cardiovascular mortality | < 65, 65–74, 75+ years (n = nearly 4 million cardiovascular deaths) | O3 |  | Daily maximum |
  Ren 2009 [91] | Time series | 95 US cities | 1987–2000 | Cardiovascular mortality | < 65, 65–74, 74+ years (n= > 4.3 million cardiovascular deaths) | O3 |  | Daily maximum |
Air pollution and pollen (n = 10) | ||||||||
 Respiratory | ||||||||
  Anderson 1998 [92] | Time series | London | Apr 1987- Feb 1992 | Asthma emergency admissions | All ages; 0–14, 15–64, 65+ years (n not reported) | O3, NO2, Black smoke, SO2 | Birch, Grass, Oak | Mean 24 h |
  Cakmak 2012 [93] | Time series | 11 Canadian cities | Apr 1994-Mar 2007 | Asthma hospital admissions | Not reported | CO, PM2.5, PM10, NO2, SO2 | Tree, Weed | Mean 24 h |
  Chen 2016 [94] | Time-series case-crossover | Adelaide, South Australia | Jul 2003- Jun 2013 | Asthma hospital admissions | 0–17, 18+ years (n = 36,024admissions) | PM2.5, NO2, PM10 | Ash tree, birch, cypress, eucalyptus, fruit tree, olive tree, pinus, plane tree, she-oak, wattle, chenopodiaceae, compositae, plantain, polygonaceae, salvation jane, grass | Daily average |
  Cirera 2012 [95] | Time series | Cartagena, Spain | Jan 1995- Dec 1998 | COPD and asthma emergency room visits, | Age not reported (n = 1617 asthma and 2322 COPD ER visits) | SO2, NO2, TSP, O3 | Poaceae, Urticaceae | Hourly mean |
  Galan 2003 [96] | Time series | Madrid, Spain | 1995–1998 | Asthma emergency department visits | Age not reported (n = 4827 asthma attacks) | SO2, PM10, NO2, O3, CO | Olea europaea, Plantago sp., Poaceae, Urticaceae | Daily mean |
  Gleason 2014 [97] | Time-stratified case-crossover | New Jersey | April - Sept 2004–2007 | Asthma emergency department visits | 3–17 years (n = 21,854 asthma ED visits) | O3, PM | Tree, grass, weed, ragweed | Daily mean |
  Goodman 2017 [98] | Time series | New York City | 1999–2009 | Asthma hospital Admissions | < 6, 6–18, 19–49, 50+ years (n = 295,497 asthma admission) | O3, PM | Tree, weed, total | Daily average, maximum, minimum |
  Krmpotic 2011 [99] | Time series | Zagreb, Croatia | Jan 2004- Dec 2006 | Asthma hospital admissions | > 18 years (n = 4125 asthma admissions) | NO2, CO, PM10 | Alder, Hazel, Birch, Hornbeam, Oak, Grasses, Ragweed | Daily minimum, maximum, mean |
  Ross 2002 [100] | Prospective Cohort | East Moline, IL | 7 months | Peak Expiratory flow rates, respiratory symptoms, frequency of asthma attacks, asthma medication use | 5–49 years (n = 59 people) | O3, PM, SO2 | Grass, Ragweed, Total | Daily mean, Maximum |
 Cardiovascular | ||||||||
  Stieb 2000 [101] | Time series | Saint John, Canada | Jul 1992- Jun 1994, Jul 1994- Mar 1996 | Cardiorespiratory emergency department visits | Age not reported (n = 19,821) | CO, H2S, NO2, O3, SO2, TRS | Ascomycetes, basidiomycetes, deuteromycetes, ferns, grass, tree, weed | Daily average |
Heat and pollen (n = 1) | ||||||||
 Silverberg 2015 [102] | Cohort Study | United States | 2006 | Pediatric hay fever | 0–17 years (n = 91,642) | – | Total | Monthly mean |