Exhibit 99.1 MONTROSE ENVIRONMENTAL GROUP ANNOUNCES FOURTH QUARTER AND FULL YEAR 2023 RESULTS - Record Full Year Revenue and Cash Flow from Operations - - Net Loss of $30.9 million; Basic and Diluted Net Loss Per Share of$1.57 - - Significant Increase in Diluted Adjusted Net Income Per Share1 - - Record Full Year Consolidated Adjusted EBITDA1 - - Expansion in Segment Level and Consolidated Adjusted EBITDA1 as Percent of Revenue for Full Year - - Continued Success Consolidating Fragmented Industry with High ...