The emergence of online political advertising has come with little regulation, allowing political advertisers on social media to avoid accountability. We analyze how transparency and accountability deficits caused by dark money and disappearing groups relate to the sentiment of political ads on Facebook. We obtained 430,044 ads with FEC-registered advertisers from Facebook's ad library that ran between August-November 2018. We compare ads run by candidates, parties, and outside groups, which we classify by (1) their donor transparency (dark money or disclosed) and (2) the group's permanence (only FEC-registered in 2018 or persistent across cycles). The most negative advertising came from dark money and disappearing outside groups, which were mostly corporations or 501(c) organizations. However, only dark money was associated with a significant decrease in ad sentiment. These results suggest that accountability for political speech matters for advertising tone, especially in the context of affective polarization on social media.

翻译：在线政治广告的兴起伴随着监管缺失，使得社交媒体上的政治广告商得以逃避问责。我们分析了“暗钱”与“消失型团体”造成的透明度和问责赤字，如何与Facebook上政治广告的情绪倾向相关联。我们从Facebook广告库中获取了2018年8月至11月期间投放的430,044条由联邦选举委员会（FEC）注册广告商发布的广告，比较了候选人、政党和外部团体投放的广告。根据（1）捐赠者透明度（暗钱或公开披露）和（2）团体存续性（仅在2018年注册于FEC或跨选举周期持续存在）进行分类。最负面的广告来自暗钱和消失型外部团体，这些团体多为企业或501(c)组织。然而，只有暗钱与广告情绪显著下降相关。这些结果表明，政治言论的问责制对广告基调至关重要，尤其是在社交媒体上情感极化加剧的背景下。