Background: Air pollution is associated with asthma mortality and hospital admissions, yet few studies have focused on exacerbations managed in the community or which subgroups of asthma patients are most vulnerable. Identifying these groups is crucial for targeted public health interventions and clinical guidance. Methods: We developed Poisson generalised regression models examining associations between short-term exposure to air pollutants (NO2, PM2.5 and PM10, and O3) and courses of oral corticosteroids (OCS) prescribed in primary care for exacerbations in a cohort of asthma-registered adults (18–80 years) in East London, between March 2019-February 2023. We analysed three time frames: pre-, during, and post-COVID-19 pandemic, and performed stratified analyses by gender, age, asthma management step, and blood eosinophil levels. Results: For every interquartile range (IQR) increase in the preceding week’s average exposure, the risk of OCS prescription increased by 5% for NO2, 2% for PM10, and 2% for PM2.5. Risk for OCS prescriptions were 2% lower during the COVID-19 period and 28% higher post-COVID-19 compared to pre-COVID-19. Stratified analyses showed that male and older adults had higher risks for NO2 associated exacerbations with same-day exposure but lower risks for one-week exposure, compared to females and younger adults. Risks were also slightly higher in patients on step 4/5 asthma medications and in those with eosinophilia, with similar patterns observed for PM10 and PM2.5. Conclusion: Short-term exposure to NO2, PM10, and PM2.5 increases the risk of mild asthma exacerbations, however risk and lag were affected by age, gender, and patient subgroups, emphasizing the need for tailored public health strategies.