Continuous measurements of surface ozone (O 3) 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 O 3 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/m 3 corresponding to an excess over the standard rates of 21%, 27%, 10%, and 40% in 2008–2011, respectively. The total oxidant level (O X = O 3 + NO 2) was high, with seasonal average concentrations up to 100 μg/m 3 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/m 3 in Tangshan. Statistical early warning analysis revealed that the O 3 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/m 3 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/m 3 and 31 °C. Similarly, the exceed-standard rate would reach 100% when O 3_mean and T _max exceeded 127 μg/m 3 and 33 °C, respectively.