Appendix: Context of Ads and Platforms in Each Country/Region

We developed a systematic analytical framework to compare the functionalities, policies, terms of use and transparency mechanisms of ad networks from four big tech companies, digital platforms and search engines
operating in the Brazilian market: Meta, Google, Twitter/X and TikTok. Our framework largely builds upon and, who argue that researchers are going through a time of low transparency and significant restrictions
over data access imposed by online platforms and big tech companies. Based on the public documentation of each ad network, evidence found in journalistic reports and the existing academic literature, we present the responsibilities these ad networks delegate to advertisers, the permissions and restrictions of their targeting systems, their advertiser verification processes and the topics that can or cannot be promoted by advertisers. In particular, we pay attention to whether or not digital advertising repositories are available and the possibility of carrying out systematic investigations based on the provided data. That is, we consider that it is not enough to simply display and present the content of the advertisements to users, but to allow for systematically collecting available data and performing analysis in depth. In the cases in which ad repositories
are available, we analyze their limitations regarding their searchability affordances, data access and data quality. Ultimately we analyze if researchers, journalists and other external auditors have found evidence of these
protocols being carried out inappropriately, especially regarding the distribution of suspicious and irregular advertising.

我们构建了一个系统分析框架，用于比较巴西市场上四家大型科技公司、数字平台及搜索引擎的广告网络（ad networks）的功能、政策、使用条款与透明度机制，涉及企业包括Meta、Google、Twitter/X和TikTok。我们的框架在很大程度上基于相关研究，这些研究指出，研究人员正面临在线平台和大型科技公司施加的透明度低下与数据访问限制严格的时期。基于各广告网络的公开文档、新闻报道中的证据及现有学术文献，我们阐述了这些广告网络赋予广告主的责任、其定向系统（targeting systems）的权限与限制、广告主验证流程（advertiser verification processes），以及广告主可推广或不可推广的主题。特别地，我们关注数字广告库（digital advertising repositories）是否可用，以及基于所提供数据开展系统性调查的可能性。也就是说，我们认为仅向用户展示广告内容是不够的，还需允许系统性收集可用数据并进行深度分析。对于广告库可用的情况，我们分析了其在可搜索性功能（searchability affordances）、数据访问及数据质量方面的局限性。最终，我们分析了研究人员、记者及其他外部审计人员是否发现这些协议（protocols）执行不当的证据，尤其是在可疑及违规广告的分发方面。