When it comes to reducing ozone, and thus smog, focusing on NOx emissions may do no good or even hurt efforts for improving air quality. Studies have been done looking at ozone (O3) precursors (nitric oxide [NO], nitrogen oxides [NOx], carbon monoxide [CO], and volatile organic compounds [VOCs])concentrations on weekdays and weekends. Despite reductions in the precursors, mostly NOx, on the weekend, ozone levels remained unchanged. Journal Abstract VOCs are the least changed between weekdays and weekends. Decreasing NOx without decreasing them may lead to increases in ozone.