Heat island simulations in Londrina city, Brazil

This work aims to study the urban heat island on North region of Parana state, Brazil and the influence of land use and urban settlements on the intensity and frequency of occurrence of these events. Through atmospheric modeling whith WRF/Chem model two simulations were made with different land and use files, one with the original land use another obtained from a composition of MODIS-Landsat imagery. The simulations showed good skills compared to observed data. Urban areas presented higher temperatures. Landsat land use has represented better urban heat islands (UHI), the gradient between urban and rural areas was well demonstrated and the correlation coefficient was above 0.92. The model underestimated the maximum values and overestimated the minimum compared with observed data in both simulations.

Radiation balance at the surface in the city of So Paulo, Brazil: diurnal and seasonal variations

The main goal of this work is to describe the diurnal and seasonal variations of the radiation balance components at the surface in the city of So Paulo based on observations carried out during 2004. Monthly average hourly values indicate that the amplitudes of the diurnal cycles of net radiation (Q*), downwelling and upwelling shortwave radiation (SW(DW), SW(UP)), and longwave radiations (LW(DW), LW(UP)) in February were, respectively, 37%, 14%, 19%, 11%, and 5% larger than they were in August. The monthly average daily values indicate a variation of 60% for Q*, with a minimum in June and a maximum in December; 45% for SW(DW), with a minimum in May and a maximum in September; 50% for SW(UP), with a minimum in June and a maximum in September; 13% for LW(DW), with a minimum in July and a maximum in January; and 9% for LW(UP), with a minimum in July and a maximum in February. It was verified that the atmospheric broadband transmissivity varied from 0.36 to 0.57; the effective albedo of the surface varied from 0.08 to 0.10; and the atmospheric effective emissivity varied from 0.79 to 0.92. The surface effective emissivity remained approximately constant and equal to 0.96. The albedo and surface effective emissivity for So Paulo agreed with those reported for urban areas in Europe and North America cities. This indicates that material and geometric effects on albedo and surface emissivity in So Paulo are similar to ones observed in typical middle latitudes cities. On the other hand, it was found that So Paulo city induces an urban heat island with daytime maximum intensity varying from 2.6A degrees C in July (16:00 LT) to 5.5A degrees C in September (15:00 LT). The analysis of the radiometric properties carried out here indicate that this daytime maximum is a primary response to the seasonal variation of daily values of net solar radiation at the surface.

On the diurnal cycle of urban aerosols, black carbon and the occurrence of new particle formation events in springtime Sao Paulo, Brazil

Large conurbations are a significant source of the anthropogenic pollution and demographic differences between cities that result in a different pollution burden. The metropolitan area of Sao Paulo (MASP, population 20 million) accounts for one fifth of the Brazilian vehicular fleet. A feature of MASP is the amount of ethanol used by the vehicular fleet, known to exacerbate air quality. The study describes the diurnal behaviour of the submicron aerosol and relies on total particle number concentration, particle number size distribution, light scattering and light absorption measurements. Modelled planetary boundary layer (PBL) depth and air mass movement data were used to aid the interpretation. During morning rush-hour, stagnant air and a shallow PBL height favour the accumulation of aerosol pollution. During clear-sky conditions, there was a wind shift towards the edge of the city indicating a heat island effect with implications on particulate pollution levels at the site. The median total particle number concentration for the submicron aerosol typically varied in the range 1.6 x 10(4)-3.2 x 10(4) cm(-3) frequently exceeding 4 x 10(4) cm-3 during the day. During weekdays, nucleation-mode particles are responsible for most of the particles by numbers. The highest concentrations of total particle number concentrations and black carbon (BC) were observed on Fridays. Median diurnal values for light absorption and light scattering (at 637 nm wavelength) varied in the range 12-33 Mm(-1) and 21-64 Mm(-1), respectively. The former one is equal to 1.8-5.0 mu g m(-3) of BC. The growth of the PBL, from the morning rush-hour until noon, is consistent with the diurnal cycle of BC mass concentrations. Weekday hourly median single-scattering albedo (omega(0)) varied in the range 0.59-0.76. Overall, this suggests a top of atmosphere (TOA) warming effect. However, considering the low surface reflectance of urban areas, for the given range of omega(0), the TOA radiative forcing can be either positive or negative for the sources within the MASP. On the average, weekend omega(0) values were 0.074 higher than during weekdays. During 11% of the days, new particle formation (NPF) events occurred. The analysed events growth rates ranged between 9 and 25 nm h(-1). Sulphuric acid proxy concentrations calculated for the site were less than 5% of the concentration needed to explain the observed growth. Thus, other vapours are likely contributors to the observed growth.