It has been reported that the abundance of nitrates in the polar region shows an 11 year periodicity which is clearly connected to solar activity. In this paper, we investigate whether or not this variation in nitrates can be explained
by solar proton events (SPE) using data of the variation in galactic cosmic rays (GCR) over two solar cycles. As the result of our analysis, it would appear that SPE do not play a major role in producing the year-to-year variability in nitrate abundance in the polar region over the 11 year solar cycle. We have found that, if the short wave length (≤ 300 nm) radiation from the Sun varies by ∼ 0.1% over
the 11 year solar cycle, the variation in nitrates can be explained naturally. The explanation requires that the intensity of GCR should increase to about 3000 times its present level. It would be useful to explore whether or not our planet has been exposed to such strong fluxes of GCR as a consequence of supernova explosions in the past
