EFFECT OF SAMPLING FREQUENCY ON TREND DETECTION FOR ATMOSPHERIC FINE MASS

A time series model was fitted by site to atmospheric fine particle ma ss data collected on a daily basis at several sites of the Eastern Fin e Particle Visibility Network. The estimated parameters from the model fitting were used in evaluating the effect of different sampling freq uencies on the sensitivity of a trend test. The presence of autocorrel ation in the data was confirmed and indicates some degree of temporal redundancy in the fine particle mass data. This redundancy was quantif ied in terms of relative variances of annual means computed for differ ent sampling frequencies and in terms of power curves for a trend test . A diminishing return in terms of power of the trend test was seen fo r increasing investments in sampling effort. As an example, an increas e in sampling rate from once every two days to once every day resulted in a maximum increase in the probability of detecting a trend of 0.04 for the scenarios examined in this report. Thus, sampling frequency c an be reduced from once per day to once every other day without a majo r penalty in terms of decreased power. In general, power of the trend test was insensitive to sampling frequency for short (less than 5 yr) or long (greater than 15 yr) time horizons. However, there were substa ntial trade-offs between sampling frequency and power of the test for intermediate time horizons (between 5 and 15 yr).