Lifetimes and timescales of tropospheric ozone

It is vital and informative to understand the lifetime and timescales of tropospheric O3 so that we can predict the impact of changing O3 sources on its abundance throughout the troposphere, and thence its climate and pollution damage.  As an example, current model intercomparison projects (MIPs) diagnose the impact of stratosphere-troposphere exchange (STE) flux of O3 into the troposphere by assuming that loss of this added O3 occurs through 3 specific reactions (O(1D)+H2O, HO2+O3, OH+O3) and is linear in O3, and that production through XO2+NO reactions is a constant.  A linearization of the full chemistry with respect to O3 clearly shows these assumptions are wrong (see ATom data, shown here).  Another example is the effort made to define odd-oxygen by a chemical family grouping (e.g., O3+O+NO2+…) to better understand the timescales for O3 loss, yet the true pattern of the odd-oxygen family should be apparent from the eigenvectors of the system. 

 

Here we define and test a new protocol for model experiments designed to understand how the coupling of O3 with the full chemistry can change the accumulation and the pattern of decay depending on the O3 source (stratosphere, surface pollution, aviation).  We take a full chemistry-transport model (UCI CTM) and generate a control run for the present day, then add direct O3 emissions (not in the control run) from (i) a large industrial region, (ii) aviation, and (iii) the mid-latitude tropopause where most STE occurs. These perturbation runs produce a seasonally varying additional O3 burden – which gives us the seasonally varying lifetime for such sources – and then we cut emissions and watch the decay pattern in terms of e-fold timescale and patterns of key species to derive the odd-oxygen family pattern.   Due to the large latitudinal and seasonal variation in reactivity rates (see ATom data: Guo et al. ACP, 23, 99–117, 2023), we expect lifetimes and timescale to vary with location and timing of O3 emissions.