Due to Beijing's high level of air pollution, there are various readings by different sources on the subject. Daily pollution readings at 27 monitoring stations around the city are reported on the website of the Beijing Environmental Protection Bureau (BJEPB). The American Embassy of Beijing also reports hourly fine particulate (PM2.5) and ozone levels on Twitter. Since the BJEPB and US Embassy measure different pollutants according to different criteria, the pollution levels and the impact to human health reported by the BJEPB are often lower than that reported by the US Embassy.