The source might be "A REPORT TO THE CALIFORNIA LEGISLATURE ON THE POTENTIAL HEALTH AND ENVIRONMENTAL IMPACTS OF LEAF BLOWERS" found here: https://ww2.arb.ca.gov/sites/default/files/2018-11/Health%20...

This is the table in the source:

  +--------------------+-------------------+-------------+---------------+
  |                    | Exhaust Emissions | New vehicle | Older vehicle |
  +--------------------+-------------------+-------------+---------------+
  | Hydrocarbons       | 199.26            | 0.39        | 201.9         |
  | Carbon Monoxide    | 423.53            | 15.97       | 1310          |
  | Particulate Matter | 6.43              | 0.13        | 0.78          |
  | Fugitive Dust      | 48.6-1031         | N/A         | N/A           |
  +--------------------+-------------------+-------------+---------------+

and the accompanying text:

> Another way to visualize the data is to compare emissions for a given amount of leaf blower operation to miles traveled by car. The Air Resources Board regularly publishes such emissions benchmarks. Thus, for the average 1999 leaf blower and car data presented in Table 9, we calculate that hydrocarbon emissions from one-half hour of leaf blower operation equal about 7,700 miles of driving, at 30 miles per hour average speed. The carbon monoxide emission benchmark is signficantly different. For carbon monoxide, one-half hour of leaf blower useage would be equivalent to about 440 miles of automobile travel at 30 miles per hour average speed.