Long-term measurement results of indoor air quality (IAQ) from 1989 to 2013 inside Pit No. 1, the largest display hall in Emperor Qin's Terra-cotta Museum (QTM), were used to evaluate the effectiveness of measures for conservation environment improvement of antiques. By comparing the results of sampling campaigns in 2013 with databases in 1989, 2004-2005, 2006-2007 and 2011, seasonal and inter-annual variation in microclimate, aerosol chemical compositions and gaseous pollutant concentrations were incorporated in estimating the probable influences of the management of the surroundings, tourist flow, excavation and restoration tasks and renovation and/or new construction work on IAQ in the QTM. After the implementation of the environmental policies in 1990s, a significant decrease of indoor particulate matter mass for the QTM was quantified. The mass concentrations of summer TSP decreased from 540.0 mu g center dot m(-3) in 1994 to 172.4 mu g center dot m(-3) in 2004, as well as the winter TSP decreased from 380.0 mu g center dot m(-3) in 1994 to 312.5 mu g center dot m(-3) in 2005. The mass concentrations of summer PM2.5 decreased from 108.4 mu g center dot m(-3) in 2004 to 65.7 mu g center dot m(-3) in 2013, as well as the winter PM2.5 decreased from 242.3 mu g center dot m(-3) in 2005 to 98.6 mu g center dot m(-3) in 2013. However, it is noted that potential hazards due to the fluctuant microclimate conditions, gaseous and secondary particulate acidic species in indoor air should still be considered to ensure the long-term preservation and conservation of the museum's artifact collection.