Abstract
Abstract. This work presents ground based differential optical absorption spectroscopy (DOAS) measurements of nitrogen dioxide (NO2) during the MILAGRO field campaign in March 2006 at the Tenango del Aire research site located to the southeast of Mexico City. The DOAS NO2 column density measurements are used in conjunction with ceilometer, meteorological and surface nitric oxide (NO), nitrogen oxides (NOx) and total reactive nitrogen (NOy) measurements to analyze pollution transport events to the southeast of Mexico City during the MILARGO field campaign. The study divides the data set into three case study pollution transport events that occurred at the Tenango del Aire research site. The unique data set is then used to provide an in depth analysis of example days of each of the pollution transport events. An in depth analysis of 13 March 2006, a Case One day, shows the transport of several air pollution plumes during the morning through the Tenango del Aire research site when southerly winds are present and demonstrates how DOAS tropospheric NO2 vertical column densities (VCD), surface NO2 mixing ratios and ceilometer data are used to determine the vertical homogeneity of the pollution layer. The analysis of 18 March 2006, a Case Two day, shows that when northerly winds are present for the entire day, the air at the Tenango del Aire research site is relatively clean and no major pollution plumes are detected. Case 3 days are characterized by relatively clean air throughout the morning with large DOAS NO2 enhancements detected in the afternoon. The analysis of 28 March 2006 show the DOAS NO2 enhancements are likely due to lightning activity and demonstrate how suitable ground-based DOAS measruements are for monitoring anthropogenic and natural pollution sources that reside above the mixing layer.
Highlights
Megacities play a critical role in local, regional and global air pollution
Using the unique data set at the Tenango del Aire research site, we present a new method to study the vertical homogeneity of the mixing layer (ML) using differential optical absorption spectroscopy (DOAS) tropospheric NO2 vertical column densities (VCD) and ceilometer mixing layer heights (MLH) data in conjunction with surface NO2 mixing ratios
Since the research site is located to the southeast of the city center, the surface mixing ratio and DOAS measurements detect various pollution plumes being transported through the research site when northerly winds exist
Summary
Megacities (cities with a population greater than 10 million) play a critical role in local, regional and global air pollution. The primary sources of pollution in Mexico City are transportation, industrial processes and domestic related activities. The high-density population, the unique geographical setting and multiple emission sources lead to high pollution episodes on a regular basis in Mexico City. These episodes have serious immediate and longer-term impacts on human health and the environment. Recent research has begun to unravel the complexity of the air pollution problem in Mexico City and its effects on a local but on a regional and global scales as well.
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