It is important to investigate the causes of sampling lag in automatic acid rain observation and propose improvement measures to enhance data timeliness. Based on comparative data from TCYII 1 type rain sensors, manual sampling buckets, and precipitation phenomenon instruments (PPI), we analyze the distribution characteristics of precipitation duration ratio (PDR) deviations and the influence of meteorological environment. The results show that the PDR value (0. 530) of automatic observation is lower than that (0. 721) of manual observation, but still higher than the PPI benchmark value (0. 316). The monthly deviation range between automatic and PPI observations varies from 0. 123 to 0. 298, with 92. 8% of individual deviations concentrated between - 0. 05 and 0. 55. The pH value fitting indicates a significant negative correlation between PDR and pH value in acid rain observations. The correlation coefficient (0. 696) for automatic observation is greater than that (0. 339) for manual observation, but is lower than the simulated PPI value (0. 906). The inferred annual average true pH values may be 4. 95 or 5. 21, higher than the automatic observation value (4. 63). The primary cause of lag is the difficulty for raindrops on the sensor surface to slide off or evaporate promptly under high humidity (> 90%), low - temperature freezing(< 0 ℃), and low evaporation (< 0. 1 mm) conditions. Adding a heating device (30 ℃) and a wind - assisted component (4. 0 m/s) can effectively enhance evaporation efficiency and reduce deviations. These findings can provide a scientific basis for optimizing the meteorological adaptability of automatic acid rain observation systems and promote the development of precise and automated meteorological observation.