SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934 (Amendment No. 1)

Arch Chemicals, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

_______03937R102_________

(CUSIP Number)

Peter D. Goldstein

GAMCO Investors, Inc.

One Corporate Center

Rye, New York 10580-1435

(914) 921-5000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

______________________September 20, 2011________________________

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box .

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) Gabelli Funds, LLC I.D. No. 13-4044523
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) 00-Funds of investment advisory clients
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e) X
6	Citizenship or place of organization New York
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power 776,103 (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power 776,103 (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person 776,103 (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 3.05%
14	Type of reporting person (SEE INSTRUCTIONS) IA, CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) GAMCO Asset Management, Inc. I.D. No. 13-4044521
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) 00-Funds of investment advisory clients
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization New York
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power 392,280 (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power 392,280 (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person 392,280 (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 1.54%
14	Type of reporting person (SEE INSTRUCTIONS) IA, CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) Gabelli Securities, Inc. I.D. No. 13-3379374
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) 00 – Client funds
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization Delaware
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power 273,969 (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power 273,969 (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person 273,969 (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 1.08%
14	Type of reporting person (SEE INSTRUCTIONS) HC, CO, IA

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) MJG Associates, Inc. I.D. No. 06-1304269
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) 00-Client Funds
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization Connecticut
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power 5,000 (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power 5,000 (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person 5,000 (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.02%
14	Type of reporting person (SEE INSTRUCTIONS) CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) Gabelli Foundation, Inc. I.D. No. 94-2975159
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) WC
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization NV
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power 40,000 (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power 40,000 (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person 40,000 (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.16%
14	Type of reporting person (SEE INSTRUCTIONS) 00-Private Foundation

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) MJG-IV Limited Partnership I.D. No. 13-3191826
	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS)
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization New York
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power 25,000 (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power 25,000 (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person 25,000 (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS)
13	Percent of class represented by amount in row (11) 0.10%
14	Type of reporting person (SEE INSTRUCTIONS) PN

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) GGCP, Inc. I.D. No. 13-3056041
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) None
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization Wyoming
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power None (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power None (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person None (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS) X
13	Percent of class represented by amount in row (11) 0.00%
14	Type of reporting person (SEE INSTRUCTIONS) HC, CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) GAMCO Investors, Inc. I.D. No. 13-4007862
	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) WC
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization New York
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power 20,500 (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power 20,500 (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person 20,500 (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS) X
13	Percent of class represented by amount in row (11) 0.08%
14	Type of reporting person (SEE INSTRUCTIONS) HC, CO

CUSIP No. 03937R102

1	Names of reporting persons I.R.S. identification nos. of above persons (entities only) Mario J. Gabelli
2	Check the appropriate box if a member of a group (SEE INSTRUCTIONS) (a) (b)
3	Sec use only
4	Source of funds (SEE INSTRUCTIONS) 00- Private Funds
5	Check box if disclosure of legal proceedings is required pursuant to items 2 (d) or 2 (e)
6	Citizenship or place of organization USA
Number Of Shares Beneficially Owned By Each Reporting Person With		: 7 : : :	Sole voting power 83,000 (Item 5)
		: 8 : : :	Shared voting power None
		: 9 : : :	Sole dispositive power 83,000 (Item 5)
		:10 : : :	Shared dispositive power None
11	Aggregate amount beneficially owned by each reporting person 83,000 (Item 5)
12	Check box if the aggregate amount in row (11) excludes certain shares (SEE INSTRUCTIONS) X
13	Percent of class represented by amount in row (11) 0.33%
14	Type of reporting person (SEE INSTRUCTIONS) IN

Item 1. Security and Issuer

This Amendment No. 1 to Schedule 13D on the Common Stock of Arch Chemicals, Inc. (the “Issuer”) is being filed on behalf of the undersigned to amend the Schedule 13D, as amended (the “Schedule 13D”), which was originally filed on August 5, 2011. Unless otherwise indicated, all capitalized terms used herein but not defined herein shall have the same meaning as set forth in the Schedule 13D.

Item 2. Identity and Background

This statement is being filed by Mario J. Gabelli (“Mario Gabelli”) and various entities which he

directly or indirectly controls or for which he acts as chief investment officer. These entities engage in various aspects of the securities business, primarily as investment adviser to various institutional and individual clients, including registered investment companies and pension plans, and as general partner or the equivalent of various private investment partnerships or private funds. Certain of these entities may also make investments for their own accounts.

The foregoing persons in the aggregate often own beneficially more than 5% of a class of equity securities of a particular issuer. Although several of the foregoing persons are treated as institutional investors for purposes of reporting their beneficial ownership on the short-form Schedule 13G, the holdings of those who do not qualify as institutional investors may exceed the 1% threshold presented for filing on Schedule 13G or implementation of their investment philosophy may from time to time require action which could be viewed as not completely passive. In order to avoid any question as to whether their beneficial ownership is being reported on the proper form and in order to provide greater investment flexibility and administrative uniformity, these persons have decided to file their beneficial ownership reports on the more detailed Schedule 13D form rather than on the short-form Schedule 13G and thereby to provide more expansive disclosure than may be necessary.

(a), (b) and (c) - This statement is being filed by one or more of the following persons: GGCP, Inc. (“GGCP”), GGCP Holdings LLC (“GGCP Holdings”), GAMCO Investors, Inc. (“GBL”), Gabelli Funds, LLC (“Gabelli Funds”), GAMCO Asset Management Inc. (“GAMCO”), Teton Advisors, Inc. (“Teton Advisors”), Gabelli Securities, Inc. (“GSI”), Gabelli & Company, Inc. (“Gabelli & Company”), MJG Associates, Inc. (“MJG Associates”), Gabelli Foundation, Inc. (“Foundation”), MJG-IV Limited Partnership (“MJG-IV”), and Mario Gabelli. Those of the foregoing persons signing this Schedule 13D are hereinafter referred to as the “Reporting Persons”.

GGCP makes investments for its own account and is the manager and a member of GGCP Holdings which is the controlling shareholder of GBL. GBL, a public company listed on the New York Stock Exchange, is the parent company for a variety of companies engaged in the securities business, including those named below.

GAMCO, a wholly-owned subsidiary of GBL, is an investment adviser registered under the Investment Advisers Act of 1940, as amended (“Advisers Act”). GAMCO is an investment manager providing discretionary managed account services for employee benefit plans, private investors, endowments, foundations and others.

GSI, a majority-owned subsidiary of GBL, is an investment adviser registered under the Advisers Act and serves as a general partner or investment manager to limited partnerships and offshore investment companies and other accounts. As a part of its business, GSI may purchase or sell securities for its own account. GSI is a general partner or investment manager of a number of funds or partnerships, including Gabelli Associates Fund, L.P., Gabelli Associates Fund II, L.P., Gabelli Associates Limited, Gabelli Associates Limited II E, ALCE Partners, L.P., Gabelli Capital Structure Arbitrage Fund LP, Gabelli Capital Structure Arbitrage Fund Limited, Gabelli Intermediate Credit Fund L.P., Gabelli Japanese Value Partners L.P., GAMA Select Energy + L.P., GAMCO Medical Opportunities L.P., GAMCO Long/Short Equity Fund, L.P., Gabelli Multimedia Partners, L.P, Gabelli International Gold Fund Limited and Gabelli Green Long/Short Fund, L.P.

Gabelli & Company, a wholly-owned subsidiary of GSI, is a broker-dealer registered under the Securities Exchange Act of 1934, as amended (“1934 Act”), which as a part of its business regularly purchases and sells securities for its own account.

Gabelli Funds, a wholly owned subsidiary of GBL, is a limited liability company. Gabelli Funds is an investment adviser registered under the Advisers Act which provides advisory services for The Gabelli Equity Trust Inc., The Gabelli Asset Fund, The GAMCO Growth Fund, The Gabelli Convertible and Income Securities Fund Inc., The Gabelli Value Fund Inc., The Gabelli Small Cap Growth Fund, The Gabelli Equity Income Fund, The Gabelli ABC Fund, The GAMCO Global Telecommunications Fund, GAMCO Gold Fund, Inc., The Gabelli Global Multimedia Trust Inc., The GAMCO Global Convertible Securities Fund, Gabelli Capital Asset Fund, GAMCO International Growth Fund, Inc., The GAMCO Global Growth Fund, The Gabelli Utility Trust, The GAMCO Global Opportunity Fund, The Gabelli Utilities Fund, The Gabelli Blue Chip Value Fund, The GAMCO Mathers Fund, The Gabelli Woodland Small Cap Value Fund, The Comstock Capital Value Fund, The Gabelli Dividend and Income Trust, The Gabelli Global Utility & Income Trust, The Gabelli Global Gold, Natural Resources, & Income Trust, The Gabelli Global Deal Fund, Gabelli Enterprise Mergers & Acquisitions Fund, The Gabelli SRI Green Fund, Inc., and The Gabelli Healthcare & Wellness Rx Trust, (collectively, the “Funds”), which are registered investment companies. Gabelli Funds is also the investment adviser to The GAMCO International SICAV (sub-fund GAMCO Stategic Value), a UCITS III vehicle.

Teton Advisors, an investment adviser registered under the Advisers Act, provides discretionary advisory services to The GAMCO Westwood Mighty Mitessm Fund, The GAMCO Westwood Income Fund and The GAMCO Westwood SmallCap Equity Fund.

MJG Associates provides advisory services to private investment partnerships and offshore funds. Mario Gabelli is the sole shareholder, director and employee of MJG Associates. MJG Associates is the Investment Manager of Gabelli International Limited and Gabelli Fund, LDC. Mario J. Gabelli is the general partner of Gabelli Performance Partnership, LP.

The Foundation is a private foundation. Mario Gabelli is the Chairman, a Trustee and the

Investment Manager of the Foundation. Elisa M. Wilson is the President of the Foundation.

Mario Gabelli is the controlling stockholder, Chief Executive Officer and a director of GGCP and Chairman and Chief Executive Officer of GBL. Mario Gabelli is also a member of GGCP Holdings. Mario Gabelli is the controlling shareholder of Teton.

MJG-IV is a family partnership in which Mario Gabelli is the general partner. Mario Gabelli has less than a 100% interest in MJG-IV. MJG-IV makes investments for its own account. Mario Gabelli disclaims ownership of the securities held by MJG-IV beyond his pecuniary interest.

The Reporting Persons do not admit that they constitute a group.

GBL, GAMCO, and Gabelli & Company are New York corporations and GSI and Teton Advisors are Delaware corporations, each having its principal business office at One Corporate Center, Rye, New York 10580. GGCP is a Wyoming corporation having its principal business office at 140 Greenwich Avenue, Greenwich, CT 06830. GGCP Holdings is a Delaware limited liability corporation having its principal business office at 140 Greenwich Avenue, Greenwich, CT 06830. Gabelli Funds is a New York limited liability company having its principal business office at One Corporate Center, Rye, New York 10580. MJG Associates is a Connecticut corporation having its principal business office at 140 Greenwich Avenue, Greenwich, CT 06830. The Foundation is a Nevada corporation having its principal offices at 165 West Liberty Street, Reno, Nevada 89501.

For information required by instruction C to Schedule 13D with respect to the executive officers and directors of the foregoing entities and other related persons (collectively, “Covered Persons”), reference is made to Schedule I annexed hereto and incorporated herein by reference.

(d) – Not applicable.

(e) – On April 24, 2008, Gabelli Funds settled an administrative proceeding with the Securities and Exchange Commission (“Commission”) regarding frequent trading in shares of a mutual fund it advises, without admitting or denying the findings or allegations of the Commission. The inquiry involved Gabelli Funds’ treatment of one investor who had engaged in frequent trading in one fund (the prospectus of which did not at that time impose limits on frequent trading), and who had subsequently made an investment in a hedge fund managed by an affiliate of Gabelli Funds. The investor was banned from the fund in August 2002, only after certain other investors were banned. The principal terms of the settlement include an administrative cease and desist order from violating Section 206(2) of the Investment Advisers Act of 1940, Section 17(d) of the Investment Company Act of 1940 (“Company Act”), and Rule 17d-1 thereunder, and Section 12(d)(1)(B)(1) of the Company Act, and the payment of $11 million in disgorgement and prejudgment interest and $5 million in a civil monetary penalty. Gabelli Funds was also required to retain an independent distribution consultant to develop a plan and oversee distribution to shareholders of the monies paid to the Commission, and to make certain other undertakings.

On January 12, 2009, Gabelli Funds settled an administrative proceeding with the Commission without admitting or denying the findings or allegations of the Commission, regarding Section 19(a) of the Company Act and Rule 19a-1 thereunder by two closed-end funds. Section 19(a) and Rule 19a-1 require registered investment companies, when making a distribution in the nature of a dividend from sources other than net investment income, to contemporaneously provide written statements to shareholders that adequately disclose the source or sources of such distribution. While the two funds sent annual statements and provided other materials containing this information, the shareholders did not receive the notices required by Rule 19a-1 with any of the distributions that were made for 2002 and 2003. As part of the settlement Gabelli Funds agreed to pay a civil monetary penalty of $450,000 and to cease and desist from causing violations of Section 19(a) and Rule 19a-1. In connection with the settlement, the Commission noted the remedial actions previously undertaken by Gabelli Funds.

(f) – Reference is made to Schedule I hereto.

Item 3. Source and Amount of Funds or Other Consideration

Item 3 to Schedule 13D is amended, in pertinent part, as follows:

The Reporting Persons used an aggregate of approximately $13,456,808 to purchase the additional Securities reported as beneficially owned in Item 5 since the most recent filing on Schedule 13D. GAMCO and Gabelli Funds used approximately $1,852,951 and $2,047,213, respectively, of funds that were provided through the accounts of certain of their investment advisory clients (and, in the case of some of such accounts at GAMCO, may be through borrowings from client margin accounts) in order to purchase the additional Securities for such clients. GSI used approximately $8,804,630 of client funds to purchase the additional Securities reported by it. GBL used approximately $678,070 of working capital to purchase the additional Securities reported by it. Mario Gabelli used approximately $73,944 of private funds to purchase the additional Securities reported by him.

Item 5. Interest In Securities Of The Issuer

Item 5 to Schedule 13D is amended, in pertinent part, as follows:

(a) The aggregate number of Securities to which this Schedule 13D relates is 1,615,852 shares, representing 6.35% of the 25,431,974 shares outstanding as reported in the Issuer’s most recently filed Form 10-Q for the quarterly period ended June 30, 2011. The Reporting Persons beneficially own those Securities as follows:

Name	Shares of Common Stock	% of Class of Common
GAMCO Gabelli Funds GSI Foundation Mario Gabelli MJG Associates MJG-IV GBL	392,280 776,103 273,969 40,000 83,000 5,000 25,000 20,500	1.54% 3.05% 1.08% 0.16% 0.33% 0.02% 0.10% 0.08%

Mario Gabelli is deemed to have beneficial ownership of the Securities owned beneficially by each of the foregoing persons. GSI is deemed to have beneficial ownership of the Securities owned beneficially by Gabelli & Company. GBL and GGCP are deemed to have beneficial ownership of the Securities owned beneficially by each of the foregoing persons other than Mario Gabelli and the Foundation.

(b) Each of the Reporting Persons and Covered Persons has the sole power to vote or direct the vote and sole power to dispose or to direct the disposition of the Securities reported for it, either for its own benefit or for the benefit of its investment clients or its partners, as the case may be, except that (i) Gabelli Funds has sole dispositive and voting power with respect to the shares of the Issuer held by the Funds so long as the aggregate voting interest of all joint filers does not exceed 25% of their total voting interest in the Issuer and, in that event, the Proxy Voting Committee of each Fund shall respectively vote that Fund’s shares, (ii) at any time, the Proxy Voting Committee of each such Fund may take and exercise in its sole discretion the entire voting power with respect to the shares held by such fund under special circumstances such as regulatory considerations, and (iii) the power of Mario Gabelli, GBL, and GGCP is indirect with respect to Securities beneficially owned directly by other Reporting Persons.

(c) Information with respect to all transactions in the Securities which were effected during the past sixty days or since the most recent filing on Schedule 13D, whichever is less, by each of the Reporting Persons and Covered Persons is set forth on Schedule II annexed hereto and incorporated herein by reference.

(e) Not applicable.

Signature

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: September 21, 2011

GGCP, INC.

MARIO J. GABELLI

MJG ASSOCIATES, INC.

GABELLI FOUNDATION, INC.

MJG-IV LIMITED PARTNERSHIP

By:/s/ Douglas R. Jamieson

Douglas R. Jamieson

Attorney-in-Fact

GABELLI FUNDS, LLC

By:/s/ Bruce N. Alpert

Bruce N. Alpert

Chief Operating Officer – Gabelli Funds, LLC

GAMCO ASSET MANAGEMENT INC.

GAMCO INVESTORS, INC.

GABELLI SECURITIES, INC.

By:/s/ Douglas R. Jamieson

Douglas R. Jamieson

President & Chief Operating Officer – GAMCO Investors, Inc.

President – GAMCO Asset Management Inc.

President – Gabelli Securities, Inc.

Schedule I

Information with Respect to Executive

Officers and Directors of the Undersigned

Schedule I to Schedule 13D is amended, in pertinent part, as follows:

The following sets forth as to each of the executive officers and directors of the undersigned: his name; his business address; his present principal occupation or employment and the name, principal business and address of any corporation or other organization in which such employment is conducted. Unless otherwise specified, the principal employer of each such individual is GAMCO Asset Management Inc., Gabelli Funds, LLC, Gabelli Securities, Inc., Gabelli & Company, Inc., Teton Advisors, Inc., or GAMCO Investors, Inc., the business address of each of which is One Corporate Center, Rye, New York 10580, and each such individual identified below is a citizen of the United States. To the knowledge of the undersigned, during the last five years, no such person has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors), and no such person was a party to a civil proceeding of a judicial or administrative body of competent jurisdiction as a result of which he was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities law or finding any violation with respect to such laws except as reported in Item 2(d) and (e) of this Schedule 13D.

GGCP, Inc. Directors:
Mario J. Gabelli	Chief Executive Officer of GGCP, Inc., and Chairman & Chief Executive Officer of GAMCO Investors, Inc.; Director/Trustee of all registered investment companies advised by Gabelli Funds, LLC.
Marc J. Gabelli	Chairman of The LGL Group, Inc. 2525 Shader Road Orlando, FL 32804
Matthew R. Gabelli	Vice President – Trading Gabelli & Company, Inc. One Corporate Center Rye, NY 10580
Charles C. Baum	Secretary & Treasurer United Holdings Co., Inc. 2545 Wilkens Avenue Baltimore, MD 21223
Fredric V. Salerno	Chairman; Former Vice Chairman and Chief Financial Officer Verizon Communications

Officers:
Mario J. Gabelli	Chief Executive Officer and Chief Investment Officer
Marc J. Gabelli	President
Michael G. Chieco	Vice President, Chief Financial Officer, Secretary
Silvio A. Berni	Vice President, Assistant Secretary and Controller

GGCP Holdings LLC Members: GGCP, Inc. Mario J. Gabelli	Manager and Member Member

GAMCO Investors, Inc. Directors:
Edwin L. Artzt Raymond C. Avansino Richard L. Bready	Former Chairman and Chief Executive Officer Procter & Gamble Company 900 Adams Crossing Cincinnati, OH 45202 Chairman & Chief Executive Officer E.L. Wiegand Foundation 165 West Liberty Street Reno, NV 89501 Former Chairman and Chief Executive Officer Nortek, Inc. 50 Kennedy Plaza Providence, RI 02903
Mario J. Gabelli Elisa M. Wilson	See above Director c/o GAMCO Investors, Inc. One Corporate Center Rye, NY 10580

Eugene R. McGrath	Former Chairman and Chief Executive Officer Consolidated Edison, Inc. 4 Irving Place New York, NY 10003
Robert S. Prather	President & Chief Operating Officer Gray Television, Inc. 4370 Peachtree Road, NE Atlanta, GA 30319
Officers:
Mario J. Gabelli	Chairman and Chief Executive Officer
Douglas R. Jamieson Henry G. Van der Eb Bruce N. Alpert Agnes Mullady Robert S. Zuccaro Christopher Michailoff	President and Chief Operating Officer Senior Vice President Senior Vice President Senior Vice President Executive Vice President and Chief Financial Officer Acting Secretary

GAMCO Asset Management Inc. Directors:
Douglas R. Jamieson Regina M. Pitaro William S. Selby
Officers:
Mario J. Gabelli	Chief Executive Officer and Chief Investment Officer – Value Portfolios

Douglas R. Jamieson Robert S. Zuccaro Chistopher J. Michailoff	President Chief Financial Officer General Counsel and Secretary
Gabelli Funds, LLC Officers:
Mario J. Gabelli	Chief Investment Officer – Value Portfolios
Bruce N. Alpert	Executive Vice President and Chief Operating Officer
Agnes Mullady	President and Chief Operating Officer – Open End Fund Division
Robert S. Zuccaro	Chief Financial Officer
Teton Advisors, Inc. Directors:
Howard F. Ward Bruce N. Alpert Nicholas F. Galluccio Robert S. Zuccaro	Chairman See above Chief Executive Officer and President Chief Financial Officer
Officers:
Howard F. Ward Nicholas F. Galluccio Robert S. Zuccaro Christopher J. Michailoff	See above See above See above Acting Secretary

Gabelli Securities, Inc.
Directors:
Robert W. Blake	President of W. R. Blake & Sons, Inc. 196-20 Northern Boulevard Flushing, NY 11358
Douglas G. DeVivo	DeVivo Asset Management Company LLC P.O. Box 2048 Menlo Park, CA 94027
Douglas R. Jamieson	President

Officers:
Douglas R. Jamieson Christopher J. Michailoff Robert S. Zuccaro	See above Secretary Chief Financial Officer
Gabelli & Company, Inc. Directors:
James G. Webster, III	Chairman
Irene Smolicz	Senior Trader Gabelli & Company, Inc.
Officers:
Daniel Miller	Office of the President
Bruce N. Alpert Diane M. LaPointe Douglas R. Jamieson	Vice President - Mutual Funds Treasurer Secretary
Gabelli Foundation, Inc. Officers:
Mario J. Gabelli	Chairman, Trustee & Chief Investment Officer
Elisa M. Wilson Marc J. Gabelli Matthew R. Gabelli Michael Gabelli	President Trustee Trustee Trustee
MJG-IV Limited Partnership Officers:
Mario J. Gabelli	General Partner

SCHEDULE II
INFORMATION WITH RESPECT TO
TRANSACTIONS EFFECTED DURING THE PAST SIXTY DAYS OR
SINCE THE MOST RECENT FILING ON SCHEDULE 13D (1)
SHARES PURCHASED AVERAGE
DATE SOLD(-) PRICE(2)

COMMON STOCK-ARCH CHEMICALS INC.

MARIO J. GABELLI
9/16/11 15,000- 46.9567
8/30/11 3,000 46.9800
8/15/11 5,000 46.7800
8/05/11 8,684 46.4595
GAMCO INVESTORS, INC.
9/20/11 3,200 46.8356
9/19/11 2,400 46.8391
9/16/11 1,200 46.9484
9/14/11 700 46.9450
9/13/11 400 46.9194
9/07/11 500 46.9469
9/06/11 300 46.9071
9/02/11 200 46.9173
9/01/11 600 46.9383
8/26/11 300 46.8400
8/22/11 1,000 46.8028
8/11/11 2,300 46.7020
8/08/11 1,400 46.0380
GAMCO ASSET MANAGEMENT INC.
9/19/11 7,000 46.8901
9/16/11 10,000 46.9600
9/16/11 1,000 46.9400
9/13/11 10,000 46.9462
8/26/11 1,000 46.8900
8/26/11 9,000 46.8919
8/24/11 1,500- 46.8200
8/22/11 3,000 46.7930
8/15/11 7,500- 46.8100
8/15/11 3,000 46.7446
8/15/11 5,000 46.7994
8/12/11 1,000- 46.7390
8/11/11 500- 46.7500
8/08/11 1,000 46.6100
GABELLI SECURITIES, INC.
9/20/11 3,200 46.8356
9/19/11 2,400 46.8391
9/16/11 1,300 46.9484
9/14/11 700 46.9450
9/13/11 400 46.9194
9/07/11 500 46.9469
9/06/11 1,700 46.9071
9/02/11 1,000 46.9173
9/01/11 2,600 46.9383
8/31/11 1,000- 46.9500
8/26/11 100 46.8400
8/22/11 700 46.8028
8/11/11 2,500 46.7020
8/09/11 300 46.1402
8/05/11 1,100 46.4967
GABELLI ASSOCIATES LIMITED II E
9/20/11 7,000 46.8356
9/19/11 5,300 46.8391
9/16/11 2,900 46.9484
9/14/11 1,600 46.9450
9/13/11 800 46.9194
9/07/11 900 46.9469
9/06/11 600 46.9071
9/02/11 700 46.9173
9/01/11 1,400 46.9383
8/26/11 600 46.8400
8/22/11 2,400 46.8028
8/11/11 4,800 46.7020
8/08/11 2,600 46.0380
GABELLI ASSOCIATES LIMITED
9/20/11 8,800 46.8356
9/19/11 6,500 46.8391
9/16/11 3,500 46.9484
9/14/11 2,000 46.9450
9/13/11 1,093 46.9194
9/07/11 1,300 46.9469
9/06/11 700 46.9071
9/02/11 100 46.9173
9/01/11 3,100 46.9383
8/26/11 600 46.8400
8/22/11 2,900 46.8028
8/11/11 200 46.7020
8/09/11 2,200 46.1402
8/05/11 6,600 46.4967
GABELLI ASSOCIATES FUND II
9/20/11 7,000 46.8356
9/19/11 5,300 46.8391
9/16/11 2,800 46.9484
9/14/11 1,500 46.9450
9/13/11 900 46.9194
9/07/11 1,000 46.9469
9/06/11 600 46.9071
9/02/11 700 46.9173
9/01/11 800 46.9383
8/26/11 600 46.8400
8/22/11 2,500 46.8028
8/11/11 100 46.7020
8/09/11 1,800 46.1402
8/05/11 5,400 46.4967
GABELLI ASSOCIATES FUND
9/20/11 14,783 46.8356
9/19/11 11,100 46.8391
9/16/11 6,155 46.9484
9/14/11 3,500 46.9450
9/13/11 1,700 46.9194
9/07/11 2,300 46.9469
9/06/11 1,000 46.9071
9/02/11 1,400 46.9173
9/01/11 3,500 46.9383
8/26/11 1,220 46.8400
8/22/11 5,000 46.8028
8/11/11 300 46.7020
8/09/11 3,900 46.1402
8/05/11 12,700 46.4967
GABELLI FUNDS, LLC.
GABELLI SMALL CAP GROWTH FUND
8/24/11 6,078 46.9200
THE GDL FUND
8/26/11 10,000 46.9024
8/16/11 4,024 46.8100
GABELLI ENTERPRISE M&A FUND
9/14/11 19,869 47.0261
9/06/11 131 46.8200
GABELLI ABC FUND
8/26/11 3,500 46.9000

(1) UNLESS OTHERWISE INDICATED, ALL TRANSACTIONS WERE EFFECTED
ON THE NYSE.

(2) PRICE EXCLUDES COMMISSION.

ARCH CHEMICALS INC SC 13D/A