Ozone concentrations are expected to rise in developing countries, potentially reducing crop yield and causing great economic losses. Therefore, an ozone biomonitoring system based on the ratio of the biomass of ozone‐resistant (NC‐R) and ozone‐sensitive (NC‐S) biotypes of white clover (Trifolium repens cv. Regal) is tested over 2 years (2012 and 2013) at four sites with neighboring crop production in the Metropolitan Region of Campinas (MRC), Brazil. The biomass production of both clones is similar at the four sites studied in the MRC, but significant differences are observed between the monthly harvests during the experimental period. Linear regression analyses show contrasting results from the experimental years. During 2012, the biomass of both clones correlated positively with precipitation and relative humidity, and negatively with vapor pressure deficit, particulate matter, nitrogen dioxide, and ozone. During 2013, the biomass production of both clones did not significantly correlate with oscillating environmental conditions. No significant linear regression between the NC‐S/NC‐R biomass ratio and ozone is found in either year. A stepwise backward multilinear method identified nitrogen dioxide and accumulated dose over a threshold of 40 ppb (AOT40) as the main parameters negatively affecting the biomasses of both clones; particulate matter affected only the sensitive clone. This field experiment shows that the current concentrations of ozone may affect sensitive Brazilian crops.