.. _ozone:

Ground-level ozone
===================

The UNECE/WHO Task Force on Health recommended the use of the SOMO35 as a relevant ozone indicator for health impact assessments (UNECE/WHO 2003). SOMO35 is calculated as the sum over the year of the daily 8-h maximum ozone concentrations in excess of a 35 ppb threshold. Based on a comprehensive meta-analysis of time series studies conducted for the World Health Organization :cite:`anderson04` and on advices received from the UNECE/ WHO Task Force on Health, the `GAINS`_ model quantifies premature mortality through an association with the SOMO35 indicator. Contrary to :math:`PM_{2.5}` `GAINS`_` does not quantify the loss of life expectancy or Years of Life Lost from exposure to ground-level ozone but only mortality impacts.

The GAINS calculation estimates the full-year daily changes in mortality as a function of daily 8-h maximum ozone concentrations, employing the concentration-response curves derived in the above-mentioned meta-analysis. The annual cases of premature mortality attributable to ozone in receptor region k are then calculated as follows: 

.. math:: 
   :nowrap:
   :label: ozone
   
   \begin{align}
   pd(k)= \frac{1}{365} d_{BL}(k) \cdot (RR_{O3}(k)-1) = \frac{1}{365} d_{BL}(k) \cdot SOMO35(k) \cdot \beta_{O_3}
   \end{align}

where:

====================    ====================================================================================================================
:math:`d_{BL}(k)`       Natural-cause baseline annual total deaths in region k
*SOMO35(k)*             Population-weighted mean SOMO35 exposure in region k expressed in :math:`\mu g ^{-3}.d`
:math:`\beta_{O_3}`           Risk coefficient corresponding to changes in relative risk for 1 :math:`\mu g ^{-3}.d` increase in exposure
====================    ====================================================================================================================

Note that, in GAINS v4.0.3, the relative risk devised by Orellano et al. :cite:`orellano20` has been implemented and will be updated pending advice from the World Health Organization in the upcoming HRAPIE2 assessment. 

.. _`GAINS`: http://gains.iiasa.ac.at/models/