Hourly isoprene concentrations in an urban forest, São Paulo megacity

Isoprene is the most abundant HC produced by vegetation, but is also produced by anthropogenic processes, as fuel burning. Their biogenic emissions are controlled by photossynthetically active radiation (PAR) and air temperature (Guenther et al., 1995; Finlayson-Pitts and Pitts, 1999). São Paulo megacity (MASP) has presented serious air pollution problems, mainly ozone and fine particulate matter. This study aims to evaluate the isoprene in an urban forest in MASP. The sampling site was located inside the University of São Paulo (USP), in the western region of MASP, it is a little green-park (~7.5 km2), with traffic along the day, and surrounded by important roads with intense traffic of vehicles. Isoprene was measured by an on-line TD-CG-FID Perkin Elmer system from 2012 to 2015, reaching 5789 samples hourly. The isoprene maximum mixing ratios was observed in summer (average 1.19 ppbv), presenting the hourly variability characteristic from biogenic emissions with maximums from 9 am to 4 pm, but not in the other seasons (Fig. 1a). The isoprene decreasing in the presence of ozone (Fig. 1b), is explained by the reactions between them. It was also possible to observe that isoprene presented different profile from NOx and NO, being the isoprene concentrations increasing continuously after 10 am (Fig. 1 b), indicating different sources. These results showed the conditions complexity controlling the atmospheric isoprene concentrations in the urban forest, including seasonality, sources, meteorological conditions and pollutants.