Cigarette smoking cessation is considered a most important intervention to reduce COPD progression . The dynamics of TD is shown in Fig 8 as cigarette smoking cessation occurs after different days of CS exposure (S = 1.67) with the parameters in Table A in S1 File. Our simulations demonstrate that when early smoking cessation happens before 920 days of CS exposure, TD falls to the baseline and COPD is prevented (Fig 8). Smoking cessation starting after day 920 leads to the reduction of TD to some extent, but COPD and inflammatory responses persist (Figure C in S1 File). Our results are qualitatively consistent with experimental and clinical observations [64–66]. Analysis of positive feedback loops will elucidate further these effects of smoking cessation as discussed later.