Background: Fine particulate matter (PM2.(5)) is one of the most harmful air pollutants, linked to serious health effects including cardiovascular and respiratory diseases, and premature mortality. Despite this, long-term data on PM2.(5) exposure and its health impacts are limited in many regions of Iran. This study aimed to assess the long-term trends of PM2.(5) concentration, estimate related health impacts, and evaluate economic costs in Khorramabad, a semi-arid city in western Iran, over a ten-year period (2014-2023). Methods: PM2.(5) data were collected from three air quality monitoring stations and analyzed for temporal trends using statistical and visualization tools. Health impacts, including all-cause, cardiovascular, COPD, and lung cancer mortality, were estimated using the WHO's AirQ + model. The data were compared with WHO air quality guidelines to assess public health risks. For estimating the economic cost attributed to PM2.(5), The human capital method (HCM) was used. Results: PM2.(5) concentrations showed significant seasonal and hourly variations, with the highest levels in summer months, particularly August. A decreasing trend in annual mean PM2.(5) was observed after 2020, with the lowest average in 2023 (16.9 mu g/m(3)). Health risk assessment revealed a declining trend in PM2.(5)-related premature deaths, from 662 in 2015 to 288 in 2023, with cardiovascular disease being the most affected outcome. The analysis revealed that over the ten-year study period, the economic burden estimation demonstrated an average annual cost of US$34.9 million (range: 19.1-43.9 million US dollars). Conclusion: Although air quality has improved in recent years, PM2.(5) levels still often exceed WHO guidelines. Continued monitoring, stricter regulations, and regional cooperation are essential to reduce pollution and its health and economic cost burden.