Assessment of rice yield and economic losses caused by ground-level O exposure in the Mekong delta region, Vietnam.

The Lower Mekong Delta region (LMD) accounts for 90% of Vietnam's rice exports; however, the air quality in the LMD is remarkably reduced by ground-level ozone (O) pollution. This study aimed to quantify the relative yield and economic value losses in rice-growing crop seasons affected by ground-level O concentrations across the LMD. The results of this study can serve as a basis for extensive assessments for the following years and support environmental managers to propose control measures of O precursor emissions (NO and VOCs) from man-made sectors, as well as build protective solutions for rice farming in LMD. Two ground-level O exposure metrics of M7 and AOT40 reflecting ground-level O pollution impacts, combined with the model of exposure-relative yield relationship (or surface O-crop models), were used to assess losses of crop production (CPL) and economic cost losses (ECL) caused by rice crop yield reductions. For the M7 metric of ground-level O exposure, the average value was 14.746 ppbV, with levels ranging from 13.959 ppbV to 15.502 ppbV, and the affected area was spread across 1309.39 thousand hectares. The AOT40 exposure metric reached an average value of 11.490 ppbV, with a range of 0.000-31.665 ppbV. The highest exposure level was 17.503-31.653 ppbV, covering an area of 747.01 thousand hectares. The total CPL of the three rice crops over the LMD was 9593.52 tonnes (accounting for 0.039% of the total value of rice production in the region), with a total corresponding EPL of 62.405 billion VND (equivalent to 2761.01 thousand USD). The results are considered a baseline study to serve as a basis for extensive assessments for the following years and support for the environmental managers to propose control measures of O precursor emissions (NO and VOCs) from man-made sectors as well as build protective solutions in rice farming in LMD shortly.