Observational Studies and a Statistical Early Warning of Surface Ozone Pollution in Tangshan, the Largest Heavy Industry City of North China

Continuous measurements of surface ozone (O3) and nitrogen oxides (NOX) at an urban site (39°37'N, 118°09'E) in Tangshan, the largest heavy industry city of North China during summertime from 2008 to 2011 are presented. The pollution of O3 was serious in the city. The daily maximum 1 h means (O3_1-hr max) reached 157 ± 55, 161 ± 54, 120 ± 50, and 178 ± 75 μg/m3 corresponding to an excess over the standard rates of 21%, 27%, 10%, and 40% in 2008-2011, respectively. The total oxidant level (OX = O3 + NO2) was high, with seasonal average concentrations up to 100 μg/m3 in summer. The level of OX at a given location was made up of NOX-independent and NOX-dependent contributions. The independent part can be considered as a regional contribution and was about 100 μg/m3 in Tangshan. Statistical early warning analysis revealed that the O3 levels would exceed the standard rate by 50% on the day following a day when the daily average ozone concentration (O3_mean) exceeded 87 μg/m3 and the daily maximum temperature (T_max) exceeded 29 °C. The exceed-standard rate would reach 80% when O3_mean and T_max exceeded 113 μg/m3 and 31 °C. Similarly, the exceed-standard rate would reach 100% when O3_mean and T_max exceeded 127 μg/m3 and 33 °C, respectively.