Understanding ozone formation at two islands of Rio de Janeiro, Brazil

Özet

This study was to evaluate the influence of vehicular emissions on two islands located in the Guanabara Bay,Metropolitan Area of Rio de Janeiro city, one of them without the presence of vehicles (Paquetá Island - PI) andanother with a considerable fleet (Governador Island - GI). The data used correspond to the hourly averages ofthe years 2012 and 2013 for nitrogen oxides (NOx, NO2 and NO), ozone (O3), carbon monoxide (CO), totalhydrocarbons (THC), aromatic hydrocarbons (BTEX), as well as meteorological data. To interpret the results, amultivariate statistic was used in order to characterize the impact of the vehicle fleet on air quality. The resultsshowed that CO and NOx levels were 2–6 times higher in GI than PI. On the other hand, THC levels were similarat both sites. Surprisingly, O3 levels were up to 1.5 times greater in PI than in GI. The possible explanation forthese higher levels is related to the formation process from THC and NOx in the presence of sunlight. The THC/NOx and NOx/NO ratios for PI are much higher than those found for GI, thus explaining the high ozone valuesfor a location with virtually no vehicle fleet and industrial activities. The benzene, toluene and xylene levels atboth sites were of the same magnitude order, however, ethyl benzene was about 7-fold higher in PI.