<em>Since</em> is the <em>subordinating conjunction</em> in the sentence "Since the science conference is on Wednesday, neither Lucy nor I can participate or attend." and its purpose is to give a reason for something, expressing the idea of <em>'in</em> <em>view of the fact that' </em>, also it is <em>introducing a subordinate clause</em>. The use of the <em>comma</em> is because the sentence started with a subordinate clause.