Weather effects on isoprene emission capacity and applications in emissions algorithms

Many plants synthesize isoprene. Because it is volatile and reacts rapidly with hydroxyl radicals, it is emitted to the atmosphere and plays a critica l role in atmospheric chemistry. Determining effective remediation efforts for ozone pollution requires accurate isoprene-emission inventories. Temper ature and light effects on isoprene emission from plants over minutes to a few hours are fairly well known, but effects over a few days (i.e., influen ced by weather) are also possible. We measured isoprene emission and photos ynthesis under constant temperature and light (known as the basal emission rate, which reflects the capacity for isoprene emission) during eight field trips from 1994 to 1996. Measurements were made at the tops of oak trees a t two sites between May and September. On six of the trips, the effect of s hort-term (minutes to hours) temperature changes was also investigated. The basal emission rate of isoprene was highly correlated with the average tem perature of the previous two days. Including the average daily dose of phot osynthetically active radiation for the previous two days improved the corr elation. Using averages from one, four, or seven days before the measuremen t resulted in lower correlation coefficients. Including a variable basal em ission rate will improve the accuracy of isoprene-emission models.