Carbon monoxide trend in the city of Rio de Janeiro via mann-kendall and cusum tests

Abstract

Hourly mean concentrations of carbon monoxide trend (CO) in the city of Rio de Janeiro (CRJ) was evaluated based on statistical tests. Air quality stations used were: Central, Copacabana, São Cristóvão and Tijuca from 2010 to 2014. The results of the CO trend based on the Mann-Kendall (MK) test showed an inverse correlation with time, with significant decrease in all seasons. Significant increase trend (Z > 0) and p-value < 0.05 were recorded in Centro and Tijuca in 2010 and 2012 with magnitude between 0.0224 and 0.0067 ppm/year. Insignificant increase occurred only in São Cristóvão (2011) for positive values (Z > 0) and p-value > 0.05. CUSUM test showed that  magnitude did not exceed the critical value at 1% and 5% probability levels. Cumulative Sum Test (CUSUM) showed homogeneous and significant CO concentrations. Significant abrupt changes occurred in the months of May, June, July, August and September and insignificant in January, February, June, August and November at 1% and 5% probability. CO concentrations occurred in the predominant directions North-Northwest (NNW), South-Southwest (SSW) and South-west (SW). Both sectors are influenced by the main synoptic systems (Frontal System and South Atlantic Subtropical High) that act on CRJ. MK and CUSUM tests proved to be efficient in evaluating trends and abrupt changes in CO concentrations and air quality stations in the CRJ.