ASSESSMENT OF URBAN TROPOSPHERIC OZONE FORMATION POTENTIAL THROUGH VOLATILE ORGANIC COMPOUNDS

Abstract

A generalized additive model (GAM) was applied to investigate the potential impacts of VOCs towards ozone concentration levels in Bangkok and vicinity areas, based on the Indices of Photochemical Ozone Creation Potential (POCP). Hydrocarbons (HCs) were found to be the group with the highest contribution to ozone production (OPC; 59.51%), whereas oxygenated HCs and halogenated HCs yielded OPC at medium (39.39%) and low (1.05%) levels. However, according to the percent change for the coefficient of determination (R2; 9.39%) and the overall mean of response (µ; 40.21%), halogenated HCs were the principal agents that affected the concentrations of urban ozone by comparison with HCs (-2.63% and 6.01%) and oxygenated HCs (-2.02% and 1.57%). In decreasing order, as validated by GAM (p < 0.05, alpha = 0.05), the model parameters that significantly increased the tropospheric ozone in Bangkok and surrounding area were 1,3-butadiene, wind direction, bromomethane, 1,2-dichloropropane, global radiation, carbon monoxide, m-xylene, 1,1,1-trichloroethane, chloromethane, trichloroethylene, 1,3,5-trimethylbenzene, o-xylene, 1,2,4-trimethylbenzene, chloroethane, 1,2-dichlorobenzene, 1,1,2-trichloroethane, oxides of nitrogen, styrene, formaldehyde, 1,4-dichlorobenzene, wind speed, 3-chloropropene, and relative humidity.

The obtained GAM regressions of the trained and estimating models were in accordance with each other with R2 = 81.24% and 82.56% coupled with noticeable performance indicators in terms of root mean squared error (RMSE) of 5.13 micrograms per cubic meter, normalized standard deviation (NSD) of 0.87, normalized absolute error (NAE) of 0.14 normalized root mean squared error (NRMSE) of 0.08, degree of agreement (d) 0.95 and normalized bias (NB) of -7.49%.