On the roof of one of the science buildings at Boston University, scientific instruments have been measuring the amount of carbon dioxide (CO2) in the air eight times per second since 2007. Carbon dioxide is the primary greenhouse gas that, because it absorbs infrared radiation emitted by the Earth, contributes to man-made climate change. Other important greenhouse gases include methane, nitrous oxide, and sulfur hexaflouride. The direct continous measurement of carbon dioxide in the atmosphere started in the 1950s at Mauna Loa, Hawaii. In that time, the global CO2 level has risen from about 316 ppm (parts per million) in 1959 to over 390 ppm today.
Daily median CO2 concentration at Boston University
|The first graph shows the daily median carbon dioxide level measured at the BU site from February 2010 through February 2012. The CO2 concentration level in Boston is almost always several ppm higher than the global average, because cities, with their buildings and vehicles burning natural gas, gasoline, and oil, are relatively large sources of CO2. For example, in May 2011 the monthly average CO2 level at Mauna Loa was 394 ppm; at BU, it was 405. The Boston data--like the data from Mauna Loa--show a dip in mid-summer, when plant photosynthesis, which removes CO2 from the atmosphere, is at a peak.|
Half-Hourly average CO2 concentration at Boston University, May 2011
|The BU equipment is part of the Boston ULTRA-EX project, a multi-disciplinary, multi-university research project seeking to understand the detailed "metabolism" of the Boston metro area from the center of Boston out to Harvard Forest. The sensitivity of the equipment allows project members to detect when wind direction is changing, traffic is backing up on the Mass Pike, or a drop in temperature triggers the lighting of furnaces, simply by the way the CO2 signal changes. The second graph, average CO2 concentration at half-hour intervals, illustrates these types of short-term variations.|