From: "Palazzolo, Michael A." <Michael.Palazzolo@alcoa.com>

To: David Putney/RTP/USEPA/US@EPA

Cc: Rochelle Boyd/RTP/USEPA/US@EPA, <bahner@rti.org>, <green@rti.org>, "Charles D. Johnson" <cdjohnson@aluminum.org>

Date: 04/07/2011 08:02 AM

Subject: Surrogate justification

David,

Please find attached a justification or rationale for using total fluoride as a surrogate 

for regulation of metals and POM from prebake potlines. The bottom line is that by 

regulating total fluoride at the MACT floor level, EPA is already limiting metals and 

POM. This justification is not applicable to POM for Soderberg potlines, but the 

Soderberg category already has a POM emissions standard. 

Please let me know if you have any questions.

Mike

Michael Palazzolo

Alcoa, Inc.

201 Isabella Street

Pittsburgh, PA 15212-5858

Ph: 412-553-4832
Attachment 1. p. 1. of 1

Total Fluoride as a Surrogate for POM and Metals from Pre-bake Anode Potlines

For pre-baked anode potlines, the Primary Aluminum MACT regulates emissions of total 

fluoride (TF), requiring:

 Monthly secondary (potroom roof) emission testing for total fluoride;

 Annual primary control device emissions testing for total fluoride;

 Daily primary control device visible emission checks; and 

 Primary control device operation within parametric limits for air flow and ore flow.

Total fluoride consists of approximately 50% particulate fluorides (PF) and 50% gaseous 

fluoride (HF). These particulate- and gas-phase pollutants are controlled using a pot hood 

capture system (typically 98%+efficiency) followed by dry alumina injection and a baghouse

(dry alumina scrubber). 

On-going compliance with the total fluoride limit, in conjunction with the associated control 

device monitoring, ensures that the pot hood capture and dry alumina scrubber systems are 

operated and maintained at the MACT floor level established by EPA for the various centerwork prebake categories. 

Metals - In addition to particulate fluoride (i.e., fluoride salts), the particulate matter released 

from an aluminum smelting pot also contains trace amounts of HAP metals. Control of these 

HAP metals is achieved using the exact same equipment that is used to control the particulate 

component of total fluoride: the pot hood capture system and dry alumina scrubber baghouse. 

So, the MACT floor technology for HAP metals is identical to that for total fluoride and control 

of total fluorides can thus be considered a surrogate for the control of HAP metals.

POM – POM emissions from an aluminum smelting pot are present as both particulate- and gasphase pollutants. Control of POM emissions is achieved using the exact same equipment that is 

used to control fluorides: the pot hood capture system and dry alumina scrubber system. 

Particulate POM are collected by the baghouse and gas-phase POM are absorbed or condensed 

on the injected alumina and then collected by the baghouse. A portion of the gas-phase POM is 

not removed and passes through the baghouse as does some fraction of gaseous fluoride (HF). 

So, the MACT floor control technology for POM is identical to that for total fluoride and control 

of total fluorides (PF and GF) and can thus be considered a surrogate for the control of POM 

emissions. (Control of POM emissions at the anode bake furnaces is similarly accomplished 

using a dry alumina scrubber system.)