Identifying Long-range Sources of Ozone Utilizing an Adjoint Method

It has been observed that local ozone concentrations can be impacted by both local emissions and by emissions that were transported from distant source regions. Thus, changes in ozone concentration in a particular region can only be understood by analyzing the precursor emission sources, such as nitrogen oxides (NOx), carbon monoxide (CO), and volatile organic compounds (VOC), over multiple regions. In this study, the primary sources of ozone concentration in seven receptor regions within North and Central America were quantitatively described by employing the GEOS-Chem model and its adjoint. The model results across all regions show that the mean contribution of natural emissions to ozone concentration is 57% less than the contribution of anthropogenic emissions. It is also observed that local emissions have a larger contribution (at least 60%) to ozone concentrations than long-range transport in all observed regions except for eastern Canada. Further results show that peak ozone concentration and transport between regions in the model mostly occur during the spring and summer months. The exception to this trend is seen in Mexico, which has its largest ozone concentration and intake of transported emissions during Northern Hemisphere winter. Overall, this study concludes that ozone concentration and transport depend on a number of factors including emission type, season and geographical location.