A new comprehensive study revealed that construction activities and vehicular traffic contribute significantly to the Delhi and National Capital Region's high concentrations of harmful air pollutants and gases. According to the World Health Organisation, air pollution was estimated to cause nearly 4.2 million premature deaths worldwide in 2016. In India, around 600,000 deaths annually are attributed to air pollution, and some of the world's highest levels can be found in Delhi city. In a study published in Sustainable Cities and Society, a team led by Surrey's Global Centre for Clean Air Research (GCARE) gathered and analysed four years of pollution data from 12 sites across Delhi, Haryana, and Uttar Pradesh, with the aim of understanding how particulate matter (PM2.5 and PM10) and gases (oxides of nitrogen, sulphur dioxide, carbon monoxide, and ozone) impact this area of India. The GCARE results show a clear trend with significantly higher levels of air pollutants in winter months than in summer or monsoon periods, with the exception of ozone levels. The high levels of fine and coarse particulate matter (PM2.5 and PM2.5-10) in winter months were attributed to fumes from crop burning upwind of Delhi and a likely increase in biomass burning for residential heating because most parts of the region do not have central heating systems. The weather during winter months - particularly reduced precipitation and low wind speeds - is also thought to play a significant role in raising pollutant levels.