Today we review research on the impact vehicle emissions have on cloud formation in the largest city in South America with a 20M population and 7 M vehicles. Such a concentration of emissions may have global impacts on precipitation. Cloud condensation nuclei in this city originate from three sources: vehicle emissions, biomass burning in the vast tropical forests and from sea-salt. Careful direct and indirect (lidart) measurements over a four month period revealed that vehicles were predominant in producing these nuclei with two diurnal maxima during rush hours.
Key Quotes:
“Atmospheric aerosol is the primary source of cloud condensation nuclei (CCN). The microphysics and chemical composition of aerosols can affect cloud development and the precipitation process.”
“The high concentrations of CCN in the air favor the formation of clouds with small droplets, which can lead to suppression of precipitation in shallow and short-lived clouds”
“Primary aerosols are emitted into the atmosphere directly by anthropogenic and natural sources. In contrast, secondary aerosols are formed in the atmosphere through the nucleation of no- or low-volatile gases containing inorganic and organic compounds, followed by growth to larger particles”
“With over 20 million inhabitants, the MASP [Metropolitan Area of São Paulo] is the biggest megacity in South America. Therefore, the MASP represents an important city for global-scale atmospheric studies. The MASP fleet comprises more than 7 million vehicles, which constitute one of the main sources of particles, together with a variety of industries and construction activities “
“The PNCs [particle number concentration]were highest between 07:00 and 19:00 LT, whereas they were lowest between 19:00 and 07:00 LT (Fig. 2b), hereafter referred to as the daytime and nighttime periods, respectively. During the daytime period, PNCs were elevated, especially during the rush hours, which are primarily associated with vehicular emissions. However, CCN peaks showed the opposite behavior, CCN concentrations being higher during the afternoon and the nighttime period. “
“in the MASP, the morning rush occurs between 07:00 and 10:00 LT, whereas the afternoon rush occurs between 17:00 to 20:00 LT. The decrease began, and the lower values of AR [Mean activation ratio] occurred, during the morning rush and formation of a secondary aerosol. Vehicular traffic and secondary aerosol formation constitute the main sources of particles in megacities such as the MASP”
“The regional atmosphere is highly affected by vehicular traffic emissions, and lower by remote sources such as biomass burning and sea-salt transport.”
“Our results show the influence that vehicular traffic, long-range transport of sea salt, biomass-burning plumes and NPF events have on CCN properties”
No comments:
Post a Comment