Continuous measurements of surface ozone (O₃) and nitrogen oxides (NO_X) 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 (O_{3_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 (O_X = O₃ + NO₂) was high, with seasonal average concentrations up to 100 μg/m³ in summer. The level of O_X at a given location was made up of NO_X-independent and NO_X-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 (O_{3_mean}) exceeded 87 μg/m³ and the daily maximum temperature (T_{_max}) exceeded 29 °C. The exceed-standard rate would reach 80% when O_{3_mean} and T_{_max} exceeded 113 μg/m³ and 31 °C. Similarly, the exceed-standard rate would reach 100% when O_{3_mean} and T_{_max} exceeded 127 μg/m³ and 33 °C, respectively.