Temporal Variations of Elemental Carbon in Beijing

Concentrations of elemental carbon (EC) in fine mode (PM2.5) were measured at Peking University in Beijing, China in four seasons from November 2005 to October 2007. The EC concentrations were measured every one- hour with a semi-continuous thermal-optical analyzer. Carbon monoxide (CO) and carbon dioxide (CO2) concentrations were measured using non-dispersive infrared absorption (NDIR) instruments with a time resolution of 1 minute. The EC and CO concentrations decreased with the increase in the wind speed (WS). The correlations of EC with CO and CO2 were generally compact throughout the measurement period and the slopes of the EC-CO and EC-CO2 correlations (¢EC/¢CO and ¢EC/¢CO2) are therefore useful parameters in investigating EC sources. The average EC concentrations for each season ranged between about 6 and 8 Êg/m3. CO showed minimum values of about 1.1 ppmv in spring-summer and maximum of about 2.1 ppmv in winter. On calm days (WS < 2m/s), the average EC concentrations started to increase at around 1800 LT and continued to increase until around 0200 LT. The ¢EC/¢CO ratios also showed similar diurnal patterns except for winter, when they showed little diurnal variation. These results suggest that there are strong EC source in Beijing during the nighttime, possibly from diesel vehicles. The high CO in winter indicates strong source of CO due to domestic heating and this lowered the ¢EC/¢CO ratios.