Variation of atmospheric Be-7 in relation to PM concentrations

Abstract

In the present study, the influences of particulate matter (PM) and seasonal monsoons on 7Be concentrations in surface air (CBe) are elucidated. The 7Be and the corresponding PM concentrations in the air were monitored simultaneously throughout a 14-year period (1998–2011) in Hsinchu, Taiwan. During the autumn and winter seasons (Oct.–Feb.), both the PM and the 7Be concentrations increased as a result of the northeasterly monsoon. In contrast, the lowest PM and 7Be concentrations were observed in July and August. This timing is due to the occurrence of southwest monsoons, which carry air masses with low PM concentrations and are associated with depleted 7Be from low latitudes. The activity concentration of 7Be in the PM (APM) was used to explain the seasonal variations of 7Be with respect to the PM concentrations. In contrast, APM is not sensitive enough to vary with the seasons. The air masses transported by the monsoons are believed to be partially mixed with the PM locally produced in Taiwan, which explains their seasonal variations. The 7Be concentrations in surface air can be experimentally predicted from the PM concentrations based on CBe (mBq/m3)=0.0767PM (μg/m3) across seasons. The annual averages of the PM and 7Be concentrations are 48.1μg/m3 and 3.7mBq/m3, respectively. The estimated CBe was either slightly overestimated or underestimated, depending on the season. The highest deviations occurred in July and August, when CBe was underestimated by 33%.