Interventions to reduce ambient particulate matter air pollution and their effect on health

Background Ambient air pollution is associated with a large burden of disease in both high‐income countries (HICs) and low‐ and middle‐income countries (LMICs). To date, no systematic review has assessed the effectiveness of interventions aiming to reduce ambient air pollution. Objectives To assess the effectiveness of interventions to reduce ambient particulate matter air pollution in reducing pollutant concentrations and improving associated health outcomes. Search methods We searched a range of electronic databases with diverse focuses, including health and biomedical research (CENTRAL, Cochrane Public Health Group Specialised Register, MEDLINE, Embase, PsycINFO), multidisciplinary research (Scopus, Science Citation Index), social sciences (Social Science Citation Index), urban planning and environment (Greenfile), and LMICs (Global Health Library regional indexes, WHOLIS). Additionally, we searched grey literature databases, multiple online trial registries, references of included studies and the contents of relevant journals in an attempt to identify unpublished and ongoing studies, and studies not identified by our search strategy. The final search date for all databases was 31 August 2016. Selection criteria Eligible for inclusion were randomized and cluster randomized controlled trials, as well as several non‐randomized study designs, including controlled interrupted time‐series studies (cITS‐EPOC), interrupted time‐series studies adhering to EPOC standards (ITS‐EPOC), interrupted time‐series studies not adhering to EPOC standards (ITS), controlled before‐after studies adhering to EPOC standards (CBA‐EPOC), and controlled before‐after studies not adhering to EPOC standards (CBA); these were classified as main studies. Additionally, we included uncontrolled before‐after studies (UBA) as supporting studies. We included studies that evaluated interventions to reduce ambient air pollution from industrial, residential, vehicular and multiple sources, with respect to their effect on mortality, morbidity and several air pollutant concentrations. We did not restrict studies based on the population, setting or comparison. Data collection and analysis After a calibration exercise among the author team, two authors independently assessed studies for inclusion, extracted data and assessed risk of bias. We conducted data extraction, risk of bias assessment and evidence synthesis only for main studies; we mapped supporting studies with regard to the types of int