The aims of this study were to investigate the impact of meteorological parameters and trace gas concentrations on daily hospital walk-ins and admissions in Chiang-Mai province, Thailand, during 2007–2013. Advanced statistical models, including t-tests, Analysis of Variance (ANOVA), Multiple Linear Regression Analysis (MLRA) and Incremental Lifetime Particulate Matter Exposure (ILPE), were constructed using meteorological data from the Pollution Control Department (PCD), Ministry of Natural Resources and Environment (MNRE), Thailand, and the Thai Meteorological Department at Chiang-Mai Province Air Quality Observatory Site (TMCS) as well as the number of walk-in and admitted patients at Nakornping Hospital, Chiang-Mai (NHCM). The results showed that all trace gaseous species and PM10 were significantly higher during the “haze episode” than during the “non-haze period.” The FTIR spectra highlight the relatively homogeneous organic functional compositions of PM2.5 collected from urban, suburban and rural observatory sites, indicating that agricultural waste burning plays an important role in air quality during the “haze episode.” The effect of age on susceptibility to respiratory diseases was investigated by separating the dataset into four groups (i.e., < 15 years, 15–59 years, 60–74 years and ≥ 75 years). The ANOVA results revealed a significant increase in hospital walk-ins and admissions for both genders in the < 15 years group (p < 0.005). MLRA revealed the significantly highest impacts of CO on hospital walk-ins for both genders. The predicted ILPE of PM10 showed the highest values for both genders during the “haze-episode” in 2007, with average values of 3.338 ± 0.576 g and 1.838 ± 0.317 g for male and female outdoor workers, respectively, over an exposure duration of 25 years.