Exhibit 31.3
CERTIFICATION PURSUANT TO
RULE 13a-14(a)/15d-14(a),
AS ADOPTED PURSUANT TO SECTION 302
OF THE SARBANES-OXLEY ACT OF 2002
I, David M. Ward, certify that:
| 1. | I have reviewed this amendment no. 1 to the annual report on Form 10-K/A of ATMI, Inc.; |
| 2. | Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report; |
Date: April 23, 2014
| /s/ David M. Ward |
| David M. Ward |
| Vice President, Controller and Principal Accounting Officer |