Depositional characteristics of ⁷Be and ²¹⁰Pb in southeastern Michigan

Abstract

[1] The depositional fluxes in the bulk and dry fallout as well as the concentrations of 7 Be and 210 Pb in aerosols were measured for a period of 17 months at Detroit, Michigan. The bulk depositional fluxes of 7 Be and 210 Pb varied between 3.11 and 63.0 dpm cm À2 yr À1 (mean of 11.4 dpm cm À2 yr À1 ) and 0.35 and 10.3 dpm cm À2 yr À1 (mean of 1.41 dpm cm À2 yr À1 ), respectively, and this variability in the depositional fluxes is attributed to the frequency and amount of precipitation and seasonal variations in the depositional fluxes. The dry depositional fluxes of 7 Be and 210 Pb contributed 2.1-19.8% and 3.6-48.6% of the bulk depositional fluxes, respectively. The higher precipitation-normalized enrichment factor for 7 Be during spring is attributed to the stratosphere-troposphere exchange of air masses during spring and large-scale atmospheric mixing during summer. We report that snow is more efficient than rain in removing 210 Pb from the atmosphere, and this is likely due to higher surface area of snow flurries compared to the rain droplets. The volume-weighted concentrations of 7 Be and 210 Pb are the highest reported in literature so far. The concentration of 7 Be in the air showed a seasonal increase during the spring and summer months, and no seasonal variation was observed for 210 Pb. The mean deposition velocities of aerosols calculated using concentrations of 7 Be and 210 Pb in air and precipitation are 1.6 and 1.1 cm s À1 , respectively, and the corresponding washout ratios are 948 and 637. There is no significant correlation between the aerosol mass and depositional velocities of 7 Be and 210 Pb in the air masses. We propose that a relatively minor portion of the aerosols actively participate in the removal of these nuclides from the air masses.

Aerosol deposition and origin in French mountains estimated with soil inventories of 210Pb and artificial radionuclides

“…McNeary and Baskaran, 2003). Even considering a first-order linear relationship between 210 Pb inventories and annual precipitations and that the y-intercept is negative (Fig.…”

Atmospheric Deposition of 7Be in the Southeast of China: A Case Study in Xiamen

“…The daily precipitation (mm d -1 ) was calculated according to the total rainfall and collection time. The average precipitation (mm d -1 ) and deposition flux (Bq m -2 d -1 ) of 7 Be in each month were calculated based on the monthly integrated equation (McNeary and Baskaran, 2007) and the specific days in each month:…”

Modeling cosmogenic radionuclides <sup>10</sup>Be and <sup>7</sup>Be during the Maunder Minimum using the ECHAM5-HAM General Circulation Model

“…Seasonal 7 Be deposition fluxes measured in Germany (Thomas Steinkopff, German Weather Service, private communication), Switzerland (Heikkilä et al, 2008a), United States (McNeary and Baskaran, 2003) and Japan (Igarashi et al, 1998) are shown in Fig. 4.…”