Seasonal and diurnal trends in black carbon properties and co-pollutants in Mexico City

Abstract

Abstract. The Mexico City metropolitan area (MCMA) is a region that continues to grow in population and vehicular traffic as well as being the largest source of short-lived climate pollutants (SLCP) in Latin America. The local city government has made significant progress in controlling some of these pollutants, i.e., ozone (O 3) and carbon monoxide (CO), but particulate matter (PM 2.5 and PM 10 ) and black carbon (BC) have shown a less positive response to mitigation strategies that have been in place for almost 3 decades. For the first time, extended measurements of equivalent black carbon (eBC), derived from light absorption measurements, have been made using a Photoacoustic Extinctiometer (PAX) over a 13 month period from March 2013 through March 2014. The daily trends in workdays (Monday through Saturday) and Sunday eBC, PM 2.5 and the co-pollutants CO, O 3 and NO x are evaluated with respect to the three primary seasons in the MCMA: rainy, cold and dry and warm and dry.The maximum values in all of the particle and gas concentrations were significantly larger (Student's t test, P <0.05) during the dry periods than in the rainy season. The changes from rainy to dry seasons for eBC, PM 2.5 , CO, O 3 and NO x were 8.8 to 13.1 µg m −3 (40 %), 49 to 73 µg m −3 (40 %), 2.5 to 3.8 ppm (40 %), 73 to 100 ppb (30 %) and 144 to 252 ppb (53 %), respectively.The primary factors that lead to these large changes between the wet and dry seasons are the accelerated vertical mixing of boundary layer and free tropospheric air by the formation of clouds that dilutes the concentration of the SLCPs, the decreased actinic flux that reduces the production of ozone by photochemical reactions and the heavy, almost daily rain that removes particulate matter.A significant "weekend effect" was also identified, particularly the decrease in BC due to fewer large transport vehicles that are fueled by diesel, which produces a large fraction of the BC. The other co-pollutant concentrations are also significantly less on weekends except for O 3 that shows no change in maximum values from workdays to Sundays. This lack of change is a result of the balancing effects of lower precursor gases, i.e., VOCs, offset by lower concentrations of NO x , that is an O 3 inhibitor.A comparison of the average maximum value of eBC measured during the 1 year period of the current study, with maximum values measured in shorter field campaigns in 2000 and 2006, shows no significant change in the eBC emissions over a 14 year period. This suggests that new methods may need to be developed that can decrease potentially toxic levels of this particulate pollutant. BackgroundShort-lived climate pollutants (SLCP) are those gases and particles whose atmospheric lifetimes range from less than a day to a few years (Shindell et al., 2012;Bowerman et al., 2013) and exert a positive radiative forcing to the global climate. These pollutants, black carbon (BC), methane (CH 4 ), tropospheric ozone (O 3 ) and selected hydrofluorocarbons (HFCs), also impact the environment and ...

Experience from Integrated Air Quality Management in the Mexico City Metropolitan Area and Singapore

“…More recently, Paredes-Miranda et al [106] compared the daily variation of BC absorption and scattering coefficients in five cities around the world and found that Mexico City has the highest values. Retama et al [107] analyzed one-year equivalent BC data (from March 2013 to March 2014) collected at SEDEMA's laboratory, which is not too far from the urban supersite during MILAGRO, and found a strong seasonal variation. The observed concentrations did not differ substantially from those of previous field campaigns, suggesting no major changes in the BC emissions.…”

Combustion-Derived Nanoparticles in Key Brain Target Cells and Organelles in Young Urbanites: Culprit Hidden in Plain Sight in Alzheimer’s Disease Development

“…The control cities have <75,000 inhabitants and, because of their small size, their levels for the main criteria air pollutants (ozone, particulate matter as PM 10 and PM 2.5 , sulfur dioxide, nitrogen dioxide, and carbon monoxide) are expected to be lower than the current US EPA standards. MC is an example of extreme urban growth and accompanying environmental pollution [65]. The metropolitan area of over 2,000 km 2 lies in an elevated basin 2,200 m above sea level surrounded on three sides by mountain ridges.…”

“…For this study, we included MC residents from the northern-industrialized and southern-residential zones. Northern residents have been exposed to higher concentrations of volatile and toxic organic compounds, PM 10 and PM 2.5 including high levels of its constituents: organic and elemental carbon, nitro-and polycyclic aromatic hydrocarbons, and metals (Zn, Cu, Pb, Ti, Mn, Sn, V, Ba), while southern residents have been exposed continuously to significant and prolonged concentrations of ozone, secondary aerosols (NO 3 − ), and PM associated with lipopolysaccharide [17,51,57,60,65]. The highest concentrations occur in the NE sector where industrial and traffic activities are prevalent, and decreased toward the SW residential area.…”

PM1 Chemical Characterization during the ACU15 Campaign, South of Mexico City

“…In general, this season is followed by a warm-dry period until May, when the rainy season starts and extends until October with an average annual rainfall of more than 1000 mm [21].…”