Diurnal Chemical Characterization of Aerosols at Downtown Mexico City During the Cold dry Seasons of 2003 and 2005. Part I. Data Validation

Data of size-differentiated (0.18-10 μm) and bulk (1, 2.5 μm) inorganic aerosols collected during February-March of 2003 and 2005 at a site near downtown Mexico City are analyzed and discussed in the present work. Physico-chemical consistency tests applied on the data base showed a reliability of 85%. Highest concentrations of PM occurred mainly in fine size ranges, i.e., accumulation mode (size-differentiated) and fine (PM1), specifically during the morning sampling periods. Sulfate, nitrate and ammonium were the dominant species though higher concentrations of NaCl were observed during the 2003 field campaign. Concentration of this species is explained in terms of the potential influence of the nearby dry salt-lake of Texcoco. Electroneutrality balances are achieved for all size ranges: PM10 (size-differentiated), PM2.5 and PM1 indicating the significant presence of gas-phase NH3 (> 40 ppb) observed consistently during the morning sampling periods in the Valley of Mexico was of importance in providing enough NH4+ to neutralize observed sulfate concentrations. Measured PM2.5 during the 2005 field campaign was exceeding several times the recent issued (November 2005) PM2.5 Mexican standard of 65 μg/m3.