Zion National Park

Normalized Total Residence Time Starting at 500 m in January 2000-2002	Normalized Total Residence Time Starting at 500 m in April 2000-2002
Normalized Total Residence Time Starting at 500 m in August 2000-2002	Normalized Total Residence Time Starting at 500 m in December 2000-2002

Monthly normalized total residence time suggests that air usually transported from south along the Colorado river and from northwest along the California coast from Spring to Fall, especially during the summer. Significant frequencies of northerly air flow patterns were also observed in the early and later fall. During the winter, air may be transported from all directions. Stagnation periods occur frequently during the winter season, resulting in relatively short distance air transports.

Normalized Total Residence Time Starting at 500 m in 20% worst days 2000-2002	Normalized Total Residence Time Starting at 500 m in 20% worst nitrate days 2000-2002

Most of the 20% worst days at Zion happened in the summer and winter, with OMC and Nitrate as the largest aerosol contributor to haze, respectively. Air flows are mainly from south along the Arizona, California and Nevada border in the 20% worst days. Northerly flow from the northern Utah and Nevada is also significantly associated with the 20% worst days, especially 20% worst nitrate days. Winter high nitrate days are more likely due to local / regional stagnation than due to nitrate transported from relatively long distance.