This article seeks to determine the levels of carbon monoxide (CO) in the air in the busiest streets of modern Lima to which pedestrians are exposed. To measure the concentration of CO, measurements were taken five days a week at three different times of the day, considering the hours with the highest traffic congestion. Also, several factors were considered, such as traffic level, time of day, day of the week, and type of transport. The measurements were taken with a Cheffort portable CO detector, and the results were recorded continuously and in real time to identify if there is a correlation between the factors and the level of this pollutant. As a result, it was determined that there is a direct and statistically significant relationship between the level of traffic and the level of carbon monoxide. In addition, the days with the highest concentration are Fridays with an average of 3...