Submicron organic aerosol in Tijuana, Mexico, from local and Southern California sources during the CalMex campaign

• Published in: Atmospheric environment (1994) Vol. 70; pp. 500 - 512
• Main Authors: Takahama, S., Johnson, A., Guzman Morales, J., Russell, L.M., Duran, R., Rodriguez, G., Zheng, J., Zhang, R., Toom-Sauntry, D., Leaitch, W.R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2013
• Subjects: ACSM; Air pollution; Border region; FTIR; NEXAFS; Organic aerosol; STXM; ISE, Mexico; Mexico, Baja California, Tijuana; INE, USA, California; STXM; ACSM; NEXAFS; Border region; FTIR; Organic aerosol; Air pollution
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2012.07.057

The CalMex campaign was conducted from May 15 to June 30 of 2010 to study the properties and sources of air pollution in Tijuana, Mexico. In this study, submicron organic aerosol mass (OM) composition measured by Fourier Transform Infrared Spectroscopy (FTIR), Aerosol Chemical Speciation Monitor (ACSM), and X-ray spectromicroscopy are combined with statistical analysis and measurements of other atmospheric constituents. The average (±one standard deviation) OM concentration was 3.3 ± 1.7 μg m−3. A large source of submicron aerosol mass at this location was determined to be vehicular sources, which contributed approximately 40% to the submicron OM; largely during weekday mornings. The O/C ratio estimated from ACSM measurements was 0.64 ± 0.19; diurnal variations in this value and the more oxygenated fraction of OM as determined from Positive Matrix Factorization and classification analyses suggest the high degree of oxygenation originates from aged OM, rather than locally-produced secondary organic aerosol. A large contribution of this oxygenated aerosol to Tijuana from various source classes was observed; some fraction of this aerosol mass may be associated with non-refractory components, such as dust or BC. Backtrajectory simulations using the HYSPLIT model suggest that the mean wind vector consistently originated from the northwest region, over the Pacific Ocean and near the Southern California coast, which suggests that the origin of much of the oxygenated organic aerosol observed in Tijuana (as much as 60% of OM) may have been the Southern California Air Basin. The marine aerosol contribution to OM during the period was on average 23 ± 24%, though its contribution varied over synoptic rather than diurnal timescales. BB aerosol contributed 20 ± 20% of the OM during the campaign period, with notable BB events occurring during several weekend evenings. ► Submicron OM composition was measured by FTIR, ACSM, and STXM during CalMex. ► The average OM concentration was 3.3 μg m−3 in Tijuana. ► Vehicular sources contributed approximately 40% to the submicron OM. ► OM measured in Tijuana was highly oxygenated (average O/C = 0.6). ► The Southern California Air Basin was a large source of oxygenated OM in Tijuana.