diff --git a/.github/workflows/R-CMD-check.yaml b/.github/workflows/R-CMD-check.yaml
index 0f2fe08..037cec0 100644
--- a/.github/workflows/R-CMD-check.yaml
+++ b/.github/workflows/R-CMD-check.yaml
@@ -29,6 +29,7 @@ jobs:
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
       R_KEEP_PKG_SOURCE: yes
+      PURPLE_AIR_API_KEY: ${{ secrets.PURPLE_AIR_API_KEY }}
 
     steps:
       - uses: actions/checkout@v4
diff --git a/README.Rmd b/README.Rmd
index 61d4620..aebcc70 100644
--- a/README.Rmd
+++ b/README.Rmd
@@ -31,6 +31,8 @@ Install the development version of PurpleAir with:
 pak::pak("cole-brokamp/PurpleAir")
 ```
 
+Querying data from the PurpleAir API requires a free [PurpleAir Developer API key](https://develop.purpleair.com/sign-in?redirectURL=%2Fdashboards%2Fkeys) linked to a Google account.
+
 ## Usage
 
 ```{r}