Two cities, two instruments
Long records, taken from the instruments themselves rather than from a forecast: sixty-six years of temperature at London Heathrow, and Beijing's air measured hour by hour by the city's own network. Rebuilt every morning.
So far in 2026, to 5 Sep — 1st of 67 years on record for the same window.
Open the recordPM2.5 24 µg/m³ over the last 24 hours, averaged across 23 stations. 6 Sep, 12:00
Open air qualityOfficial Met Office daily figures for Heathrow via ECA&D (KNMI) through 31 Jul 2026; the days after that are derived from the airport's own METAR reports via the Iowa Environmental Mesonet, current to 5 Sep 2026. METAR-derived maxima run a little below the official figures on the hottest days — half-hourly sampling misses a brief afternoon peak — so this year's tail is a close estimate, not the final count.
Beijing Capital Airport, station 54511. NOAA's official daily series is complete to 2012 and then falls apart, so the gaps and everything after are filled from the same airport's METAR reports. Thresholds are five degrees above London's, and 35 °C is the China Meteorological Administration's own high-temperature warning line rather than a round number.
PM2.5 measured hourly by Beijing's municipal monitoring network and published through the China National Environmental Monitoring Centre. The historical series is the city mean across its stations, excluding the designated clean-air control site at Dingling and the regional background site, both of which measure something other than the city's air. Concentrations are in µg/m³ and every index on this page is computed from them here, so the two scales are judging identical numbers.
A GitHub Action rebuilds every page each morning and commits the result, so the site is never more than a day behind its sources. The Beijing air-quality tile goes further and asks the monitoring network directly each time the page is opened.