Abstract: Since 2013, the annual average mass concentration of PM_2.5 in Beijing’s urban area has been decreasing annually, but heavy PM_2.5 pollution incidents have continued to occur frequently. Moreover, there exist many uncertainties regarding the causes as well as the physical and the chemical mechanisms of the rapid or even the explosive growth of the pollution. This study analyzes the thresholds of conventional meteorological elements, PM_2.5, and its chemical components under the three growth mechanisms, slow, rapid, and explosive, as well as the correlation between the changes in meteorological elements and increase in the pollutant concentration from 2013 to 2020 in Beijing’s urban area. The results showed that from 2013 to 2020, the average accumulation rate of PM_2.5 had a slowing trend, and the proportion of slow growth in the accumulation phase of PM_2.5 increased annually in Beijing. Under the premise that the criterion is gradually strict, the proportion of explosive growth has not shown a drastic change yearly (4%–7%). The PM_2.5 concentration threshold for an explosive increase from 2013 to 2016 was 62 µg m⁻³. After 2017, the threshold was strict to 45 µg m⁻³, which has become 82 µg m⁻³ since 2018. After this value, the probability of explosive growth will increase significantly. Organic aerosol (Org) played a vital role in the explosive growth. In the same time interval, the order of the contribution of Org to the growth concentration of submicron aerosol species (PM₁) is slow growth < fast growth < explosive growth. The contribution of primary OA (POA) in the rapid and burst growth to the Org growth concentration on average exceeds 50%, which is higher than the average proportion of 40% during the study period. Among the inorganic components, the contribution of SO₄²⁻ in the increasing concentration of PM₁ shows the order of explosive growth (13%) > fast growth (11.8%) > slow growth (11.1%). Meanwhile, the opposite is observed for the contribution of NO₃⁻. The contribution of secondary particulate matter (SPM) in the cumulative phase is higher than that of the primary particulate matter (PPM). However, the contribution of PPM to the pollution increase (up to 45%) in the explosive growth is significantly higher than 33% in the average period, indicating that the contribution of PPM to the explosive growth cannot be underestimated. After the explosive growth began, the temperature and pressure both decreased, while the humidity increased significantly in autumn and winter. The main air mass in the explosive growth is southward (the three heights account for 69%–82%), followed by the eastward direction (12%–20%) in Beijing’s urban area.