Measurements of Heavy Metals in Dry and Wet Deposition in São Paulo City - Highway and Urban Environment - page 98

Site Sampling
São Paulo City, with a territorial area over 1,528 km 2 , is located in the southeastern
region of São Paulo state, Brazil, ~45 km from the coast and 780 m above sea level.
With almost 11 million inhabitants, it is the largest part of the Metropolitan Area of
the São Paulo (MASP) with more than 17 million inhabitants. The main sources of
pollution in the city are vehicular and industrial emissions. Diesel, hydrated ethanol,
natural gas and gasohol (a mix of 22-25% in ethanol + gasoline) are the most
common fuels used in more than 7 million heavy and light vehicles. The vehicular
fleet was responsible for 40% of the 67,000 t PM 10 emitted in the MASP in 2003.
From this, 10% is released by industrial processes, 25% by secondary aerosol formation
and the remaining by resuspended road dust [1] . The site sampling was located in
the center of São Paulo City (23°32¢ SE 46°39¢ W) surrounded by large avenues
with intense flux of vehicles.
Experimental
Rainwater samples were collected on the top of a building (15 m above ground)
within the campus of Mackenzie University, by an automatic wet-only rainwater
collector G.K. Walter model 211. After collection, the rainwater samples were
filtered through a 0.22 mm cellulose acetate membrane and then acidified with HNO 3
(pH = 2) and stored in 50 mL high-density polyethylene flasks at 4°C until the
analysis. The aerosol particles were sampled by a portable sampler called “Mini-Vol”
(Airmetrics, USA) during the winter season; July 7 to September 5, 2003. The particle
sampler separates the aerosol particles as coarse (2.5-10 mm equivalent aerodynamic
diameter, EAD) and fine (<2.5 mm EAD) using Nuclepore filters with 8 and 0.4 mm
pore size, respectively. The particle mass loading on the filters was determined
gravimetrically. The soluble metals were extracted under mechanical shaking in 25 mL
ultra-pure water for 1 h, followed of acidification with 0.1% HNO 3 .
Reagents and Solutions
All reagents were of analytical grade. The ultrapure nitric acid used for conditioning
the samples was prepared by sub-boiling distillation using Marconi system
(Piracicaba, Brazil). The solutions were prepared by using ultrapure water obtained
from a Nanopure ® system (resistivity >18 MW cm). Copper, lead, cadmium and
zinc stock solutions (0.010 mol/L) were prepared by dissolution of its nitrate salts
in 10 mmol/L HNO 3 solutions. The solutions with lower metal ion concentration
were diluted daily from the stock solution in 10 mmol/L HNO 3 , which was also
used as carrier electrolyte for copper, lead and cadmium. A 10 mmol/L acetate
buffer solution (pH 4.5) was used as electrolyte for zinc determinations. Mercury
was chemically purified and bi-distilled under vacuum.