Short-term secondary organic carbon estimations with a modified OC/EC primary ratio method at a suburban site in Madrid (Spain)

A time series of more than two years of continuous measurements of EC, OC and TC obtained with a Rupprecht and Patashnick (R&P) thermal analyzer at a suburban site in Madrid has been evaluated in this work. Correction factors obtained from intercomparison exercises with thermo-optical methods were applied to the original measurements. Corrected OC and EC mean values are 3.7 and 1.3 μg m−3 respectively. The highest individual values have been recorded in winter. No seasonal variation has been observed in OC, whereas a slight decrease of EC is observed in summer, leading to higher OC/EC ratios. The mean value of the OC/EC ratio is 4.9. Daily patterns show maximum EC and OC associated to traffic rush hours, with a delay of the OC peak related to the formation of SOC. Daily oscillation is more pronounced in winter. Hourly estimations of SOC production have been obtained by the primary OC/EC ratio approach, after discounting the OC, EC background contamination. A mean primary ratio value of 0.59 has been used for SOC short-term estimations throughout the entire time period. As expected, the highest SOC production is observed in summer, related to the increasing in photochemical activity, which also influences daily patterns and the time of the daily SOC maximum. In summer the daily SOC production ranges from 80 to 92%, whereas in the winter months it varies from 70 to 84%. These SOC estimations do not discount primary biogenic or natural contributions to OC and are therefore maximum values.