On the Influence of Pre- and In-seasonal Meteorological Conditions on Grass Pollen Interannual Variations in the UK

Up to 30% of the UK population are sensitized to grass pollen. Therefore, grass pollen is considered the most allergenic pollen type in the UK. Estimating the grass pollen season severity and interannual variation is a key task in aerobiological studies. The season severity is quantified using the Seasonal Pollen Integral (SPIn) - the integral over time of daily pollen concentration. This severity is tightly connected to personal exposure and the symptoms among hay fever sufferers. Recent studies suggest that the SPIn interannual variation is related to variation in pre- and in-seasonal meteorological conditions at the specific region. Here, we investigate whether the SPIn interannual variation can be explained by variation in pre-seasonal precipitation and in-seasonal air temperatures in the UK. Seven UK pollen observation sites have been chosen in the study: Worcester, Plymouth, Isle of Wight, Belfast, York, Islington (London) and Ipswich. The pollen observations cover the 1996-2018 grass pollen seasons, where we include those years without substantial gaps in the daily time series, thereby providing 116 pollen seasons to be included in the study. Maximum daily air temperature and precipitation data have been taken from the global summary of the day meteorological dataset. The SPIn, temperature and precipitation data have been transformed to interannual variations relatively mean value at each pollen observation site. The transformed time series have been analysed by looking for correlation between variations in pre-seasonal precipitation, in-seasonal air temperature and SPIn. The results show positive and significant correlation between pre-seasonal precipitation and SPIn variations (R = 0.35, p-value < 0.001) at the selected sites. Station-wise, the correlation is positive and significant at Worcester (R = 0.54, p-value < 0.01) and Ipswich (R = 0.81, p-value < 0.05). Correlation between in-seasonal air temperature and SPIn variations is also positive and significant (R = 0.33, p-value < 0.001) at the sites. Station-wise, the correlation coefficient is positive and significant at Worcester, Plymouth and Islington (R = 0.51, 0.50, 0.59, respectively p-value < 0.05). The study indicates that the SPIn variation is not a regional scale phenomenon in the UK. Instead, it appears to be related to local environmental effects. It is also shown that the pre- and in-seasonal meteorological conditions are statistically correlated with the SPIn, which may be explained by the fact that governing processes affecting the SPIn are related to both pollen production (pre-season) and atmospheric conditions (in-season).