Global impact of monocyclic aromatics on tropospheric composition

Abstract. Aromatic compounds are reactive species influencing ozone formation, OH concentrations and organic aerosol formation. An assessment of their impacts on the gas-phase composition at a global scale has been performed using a general circulation atmospheric-chemistry model.

Globally, we found a small annual average net decrease (less than 3 %) in global OH, ozone, and NO_x mixing ratios when aromatic compounds are included in the chemical mechanism. This inclusion of aromatics also results in CO mixing ratio increases, which cause a general decrease in OH concentrations. The largest changes are found in glyoxal and NO₃, with increases in the atmospheric burden of 10 % and 6 %, respectively.

Regionally, significant differences were found particularly in high NO_x regime areas, with an increase of up to 4 % in O₃ mixing ratios and 8 % in OH concentrations. NO₃ increased by more than 30 % in several regions of the northern hemisphere, and glyoxal increased up to 40 % in Europe and Asia. Large increases in formaldehyde were found in urban areas.

Although the relative impact of aromatics at the global scale is limited, at a regional level they are important in atmospheric chemistry.