<PAGE>

                                                                    EXHIBIT 10.6

                      FORM OF COMMON STOCK PURCHASE WARRANT


                                      143
<PAGE>

THIS COMMON STOCK PURCHASE WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"). THE HOLDER HEREOF, BY PURCHASING
THIS COMMON STOCK PURCHASE WARRANT, AGREES FOR THE BENEFIT OF THE COMPANY THAT
SUCH SECURITIES MAY BE OFFERED, SOLD OR OTHERWISE TRANSFERRED ONLY (A) TO THE
COMPANY, (B) PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES
ACT, OR (C) IF REGISTERED UNDER THE SECURITIES ACT AND ANY APPLICABLE STATE
SECURITIES LAWS. IN ADDITION, A SECURITIES PURCHASE AGREEMENT ("PURCHASE
AGREEMENT"), DATED THE DATE HEREOF, A COPY OF WHICH MAY BE OBTAINED FROM THE
COMPANY AT ITS PRINCIPAL EXECUTIVE OFFICE, CONTAINS CERTAIN ADDITIONAL
AGREEMENTS AMONG THE PARTIES, INCLUDING, WITHOUT LIMITATION, PROVISIONS WHICH
LIMIT THE EXERCISE RIGHTS OF THE HOLDER AND SPECIFY MANDATORY REDEMPTION
OBLIGATIONS OF THE COMPANY.

                     ---------------------------------------

                             EMISSIONS TESTING, INC.

                          COMMON STOCK PURCHASE WARRANT


--------------------------------------------------------------------------------
                                                      No. 2

Number of shares: 50,000                   Holder:  GCA Strategic Investment
                                                    Fund Limited
Expiration Date:  September 15, 2005                c/o Prime Management Limited

                                                    Mechanics Building
Purchase Price Per Share:  $1.00                    12 Church Street
                                                    Hamilton, Bermuda, HM11

   For identification only. The governing terms of this Warrant are set forth
                                     below.
--------------------------------------------------------------------------------

eMissions Testing, Inc., a Georgia corporation (the "COMPANY"), hereby certifies
that, for value received, GCA Strategic Investment Fund Limited or assigns, is
entitled, subject to the terms set forth below, to purchase from the Company at
any time or from time to time after the date hereof and prior to the fifth
anniversary hereof (the "EXERCISE PERIOD"), at the Purchase Price hereinafter
set forth, Fifty Thousand (50,000) shares of the fully paid and nonassessable
shares of common stock of the Company, no par value per share (the "Common
Stock"). The number and character of such shares of Common Stock and the
Purchase Price are subject to adjustment as provided herein.

      The purchase price per share of Common Stock issuable upon exercise of
this Warrant (the "PURCHASE Price") shall initially be $1.00; PROVIDED, HOWEVER,
that the Purchase Price shall be adjusted from time to time as provided herein.


                                      144
<PAGE>

      Capitalized terms used herein not otherwise defined shall have the
meanings ascribed thereto in the Purchase Agreement. As used herein the
following terms, unless the context otherwise requires, have the following
respective meanings:

            (a) The term "COMPANY" shall include eMissions Testing, Inc. and any
      corporation that shall succeed or assume the obligations of such
      corporation hereunder.

            (b) The term "COMMON STOCK" includes (a) the Company's common stock,
      no par value per share, (b) any other capital stock of any class or
      classes (however designated) of the Company, authorized on or after such
      date, the Holders of which shall have the right, without limitation as to
      amount, either to all or to a share of the balance of current dividends
      and liquidating dividends after the payment of dividends and distributions
      on any shares entitled to preference, and the Holders of which shall
      ordinarily, in the absence of contingencies, be entitled to vote for the
      election of a majority of directors of the Company (even though the right
      so to vote has been suspended by the happening of such a contingency) and
      (c) any other securities into which or for which any of the securities
      described in (a) or (b) may be converted or exchanged pursuant to a plan
      of recapitalization, reorganization, merger, sale of assets or otherwise.

            (c) The term "OTHER SECURITIES" refers to any stock (other than
      Common Stock) and other securities of the Company or any other person
      (corporate or otherwise) that the Holder of this Warrant at any time shall
      be entitled to receive, or shall have received, on the exercise of this
      Warrant, in lieu of or in addition to Common Stock, or that at any time
      shall be issuable or shall have been issued in exchange for or in
      replacement of Common Stock or Other Securities pursuant to Section 4 or
      otherwise.

      1. EXERCISE OF WARRANT.

            1.1 METHOD OF EXERCISE.

            (a) This warrant may be exercised in whole or in part (but not as to
      a fractional share of Common Stock), at any time and from time to time
      during the Exercise Period by the Holder hereof by delivery of a notice of
      exercise (a "NOTICE OF EXERCISE") substantially in the form attached
      hereto as EXHIBIT A via facsimile to the Company. Promptly thereafter the
      Holder shall surrender this Warrant to the Company at its principal
      office, accompanied by payment of the Purchase Price multiplied by the
      number of shares of Common Stock for which this Warrant is being exercised
      (the "EXERCISE PRICE"). Payment of the Exercise Price shall be made, at
      the option of the Holder, (i) by check or bank draft payable to the order
      of the Company, or (ii) by wire transfer to the account of the Company.
      Upon exercise, the Holder shall be entitled to receive, promptly refund
      the excess to the Holder. Upon exercise, the Holder shall be entitled to
      receive, promptly after payment in full, one or more certificates, issued
      in the Holder's name or in such name or names as the Holder may direct,
      subject to the


                                      145
<PAGE>

      limitations on transfer contained herein, for the number of shares of
      Common Stock so purchased. The shares of Common Stock so purchased shall
      be deemed to be issued as of the close of business on the date on which
      the Company shall have received from the Holder payment in full of the
      Exercise Price (the "EXERCISE DATE").

            (b) Notwithstanding anything to the contrary set forth herein, upon
      exercise of all or a portion of this Warrant in accordance with the terms
      hereof, the Holder shall not be required to physically surrender this
      Warrant to the Company. Rather, records showing the amount so exercised
      and the date of exercise shall be maintained on a ledger substantially in
      the form of ANNEX B attached hereto (a copy of which shall be delivered to
      the Company or transfer agent with each Notice of Exercise). It is
      specifically contemplated that the Holder hereof shall act as the
      calculation agent for all exercises of this Warrant. In the event of any
      dispute or discrepancies, such records maintained by the Holders shall be
      controlling and determinative in the absence of manifest error. The Holder
      and any assignee, by acceptance of this Warrant, acknowledge and agree
      that, by reason of the provisions of this paragraph, following an exercise
      of a portion of this Warrant, the number of shares of Common Stock
      represented by this Warrant will be the amount indicated on ANNEX B
      attached hereto (which may be less than the amount stated on the face
      hereof).

            1.2 REGULATION D RESTRICTIONS. The Holder hereof represents and
warrants to the Company that it has acquired this Warrant and anticipates
acquiring the shares of Common Stock issuable upon exercise of the Warrant
solely for its own account for investment purposes and not with a view to or for
resale of such securities unless such resale has been registered with the
Commission or an applicable exemption is available therefore. At the time this
Warrant is exercised, the Company may require the Holder to state in the Notice
of Exercise such representations concerning the Holder as are necessary or
appropriate to assure compliance by the Holder with the Securities Act.

            1.3 COMPANY ACKNOWLEDGMENT. The Company will, at the time of the
exercise of this Warrant, upon request of the Holder hereof, acknowledge in
writing its continuing obligation to afford to such Holder the registration
rights to which such Holder shall continue to be entitled after such exercise in
accordance with the provisions of a Registration Rights Agreement dated the date
hereof (the "Registration Rights Agreement"). If the Holder shall fail to make
any such request, such failure shall not affect the continuing obligation of the
Company to afford such Holder any such rights.

            1.4 LIMITATION ON EXERCISE. Notwithstanding the rights of the Holder
to exercise all or a portion of this Warrant as described herein, such exercise
rights shall be limited, solely to the extent set forth in the Purchase
Agreement as if such provisions were specifically set forth herein. In addition,
the number of shares of Common Stock issuable upon exercise of this Warrant is
subject to reduction as specified in Section 10.3 of the Purchase Agreement.


                                      146
<PAGE>

      2. DELIVERY OF STOCK CERTIFICATES, ETC., ON EXERCISE. As soon as
practicable after the exercise of this Warrant, and in any event within five (5)
business days thereafter, the Company at its expense (including the payment by
it of any applicable issue, stamp or transfer taxes) will cause to be issued in
the name of and delivered to the Holder thereof, or, to the extent permissible
hereunder, to such other person as such Holder may direct, a certificate or
certificates for the number of fully paid and nonassessable shares of Common
Stock (or Other Securities) to which such Holder shall be entitled on such
exercise, plus, in lieu of any fractional share to which such Holder would
otherwise be entitled, cash equal to such fraction multiplied by the then
applicable Purchase Price, together with any other stock or other securities and
property (including cash, where applicable) to which such Holder is entitled
upon such exercise pursuant to Section 1 or otherwise.

      3. ADJUSTMENT FOR EXTRAORDINARY EVENTS. The Purchase Price to be paid by
the Holder upon exercise of this Warrant, and the consideration to be received
upon exercise of this Warrant, shall be adjusted in case at any time or from
time to time pursuant to Article XI of the Purchase Agreement as if such
provisions were specifically set forth herein.

      4. NO IMPAIRMENT. The Company will not, by amendment of its Certificate of
Incorporation or through any reorganization, transfer of assets, consolidation,
merger, dissolution, issue or sale of securities or any other voluntary action,
avoid or seek to avoid the observance or performance of any of the terms of this
Warrant, but will at all times in good faith assist in the carrying out of all
such terms and in the taking of all such action as may be necessary or
appropriate in order to protect the rights of the Holder of this Warrant against
impairment. Without limiting the generality of the foregoing, the Company (a)
will not increase the par value of any shares of stock receivable on the
exercise of this Warrant above the amount payable therefor on such exercise, (b)
will take all such action as may be necessary or appropriate in order that the
Company may validly and legally issue fully paid and unassessable shares of
stock on the exercise of this Warrant, and (c) will not transfer all or
substantially all of its properties and assets to any other person (corporate or
otherwise), or consolidate with or merge into any other person or permit any
such person to consolidate with or merge into the Company (if the Company is not
the surviving person), unless such other person shall expressly assume in
writing and will be bound by all the terms of this Warrant.

      5. ACCOUNTANT'S CERTIFICATE AS TO ADJUSTMENTS. In each case of any
adjustment or readjustment in the shares of Common Stock (or Other Securities)
issuable on the exercise of this Warrant, the Company at its expense will
promptly cause independent certified public accountants of national standing
selected by the Company to compute such adjustment or readjustment in accordance
with the terms of this Warrant and prepare a certificate setting forth such
adjustment or readjustment and showing in detail the facts upon which such
adjustment or readjustment is based, including a statement of (a) the
consideration received or receivable by the Company for any additional shares of
Common Stock (or Other Securities) issued or sold or deemed to have been issued
or sold, (b) the number of shares of Common Stock (or Other Securities)
outstanding or deemed to be outstanding, and (c) the Purchase Price and the
number of shares of Common Stock to be received upon exercise of this Warrant,
in effect immediately prior to such issue or sale and as adjusted and readjusted
as provided in this Warrant. The Company will forthwith mail a copy of each such
certificate to the Holder of this Warrant, and will, on the written request at
any time of the Holder of this Warrant, furnish to such Holder a


                                      147
<PAGE>

like certificate setting forth the Purchase Price at the time in effect and
showing how it was calculated.

      6. NOTICES OF RECORD DATE, ETC. In the event of

                  (a) any taking by the Company of a record of the Holders of
      any class or securities for the purpose of determining the Holders thereof
      who are entitled to receive any dividend or other distribution, or any
      right to subscribe for, purchase or otherwise acquire any shares of stock
      of any class or any other securities or property, or to receive any other
      right, or

                  (b) any capital reorganization of the Company, any
      reclassification or recapitalization of the capital stock of the Company
      or any transfer of all or substantially all the assets of the Company to
      or consolidation or merger of the Company with or into any other person,
      or

                  (c) any voluntary or involuntary dissolution, liquidation or
      winding- up of the Company,

then and in each such event the Company will mail or cause to be mailed to the
Holder of this Warrant a notice specifying (i) the date on which any such record
is to be taken for the purpose of such dividend, distribution or right, and
stating the amount and character of such dividend, distribution or right, and
(ii) the date on which any such reorganization, reclassification,
recapitalization, transfer, consolidation, merger, dissolution, liquidation or
winding-up is to take place, and the time, if any, as of which the Holders of
record of Common Stock (or Other Securities) shall be entitled to exchange their
shares of Common Stock (or Other Securities) for then and in each such event the
Company will mail or cause to be mailed to the Holder of this Warrant a notice
specifying (i) the date on which any such record is to be taken for the purpose
of such dividend, distribution or right, and stating the amount of character of
such dividend, distribution or right, and (ii) the date on which any such
reorganization, reclassification, recapitalization, transfer, consolidation,
merger, dissolution, liquidation or winding-up is to take place, and the time,
if any, as of which the Holders of record of Common Stock (or Other Securities)
shall be entitled to exchange their shares of Common Stock (or Other Securities)
for securities or other property deliverable on such reorganization,
reclassification, recapitalization, transfer, consolidation, merger,
dissolution, liquidation or winding-up. Such notice shall be mailed at least 20
days prior to the date specified in such notice on which any action is to be
taken.

      7. RESERVATION OF STOCK, ETC. ISSUABLE ON EXERCISE OF WARRANT. The Company
will at all times reserve and keep available, solely for issuance and delivery
on the exercise of this Warrant, all shares of Common Stock (or Other
Securities) from time to time issuable on the exercise of this Warrant.


                                      148
<PAGE>

      8. EXCHANGE OF WARRANT.

            (a) On surrender for exchange of this Warrant, properly endorsed and
in compliance with the restrictions on transfer set forth in the legend on the
face of this Warrant, to the Company, the Company at its expense will issue and
deliver to or on the order of the Holder thereof a new Warrant of like tenor, in
the name of such Holder or as such Holder (on payment by such Holder of any
applicable transfer taxes) may direct, calling in the aggregate on the face or
faces thereof for the number of shares of Common Stock called for on the face of
the Warrant so surrendered.

            (b) Upon written notice from the Purchasers that the Purchasers have
elected to transfer amongst each other a portion of this Warrant, and on
surrender for amendment and restatement of this Warrant, the Company at its
expense will issue and deliver to or on the order of the Holder thereof a new
Warrant of like tenor, in the name of such Holder as the Purchasers (on payment
by such Holder of any applicable transfer taxes) may direct, calling in the
aggregate on the face or faces thereof for the number of shares of Common Stock
as set forth in such notice reflecting such transfer.

      9. REPLACEMENT OF WARRANT. On receipt of evidence reasonably satisfactory
to the Company of the loss, theft, destruction or mutilation of this Warrant
and, in the case of any such loss, theft or destruction of this Warrant, on
delivery of an indemnity agreement or security reasonably satisfactory in form
and amount to the Company or, in the case of any such mutilation, on surrender
and cancellation of this Warrant, the Company at its expense will execute and
deliver, in lieu thereof, a new Warrant of like tenor.

      10. REMEDIES. The Company stipulates that the remedies at law of the
Holder of this Warrant in the event of any default or threatened default by the
Company in the performance of or compliance with any of the terms of this
Warrant are not and will not be adequate, and that such terms may be
specifically enforced by a decree for the specific performance of any agreement
contained herein or by an injunction against a violation of any of the terms
hereof or otherwise.

      11. NEGOTIABILITY, ETC.. This Warrant is issued upon the following terms,
to all of which each Holder or owner hereof by the taking hereof consents and
agrees:

            (a) title to this Warrant may be transferred by endorsement and
delivery in the same manner as in the case of a negotiable instrument
transferable by endorsement and delivery.

            (b) any person in possession of this Warrant properly endorsed is
authorized to represent himself as absolute owner hereof and is empowered to
transfer absolute title hereto by endorsement and delivery hereof to a BONA FIDE
purchaser hereof for value; each prior taker or owner waives and renounces all
of his equities or rights in this Warrant in favor of such BONA FIDE purchaser,
and each such BONA FIDE purchaser shall acquire absolute title hereto and to all
rights represented hereby;


                                      149
<PAGE>

            (c) until this Warrant is transferred on the books of the Company,
the Company may treat the registered Holder hereof as the absolute owner hereof
for all purposes, notwithstanding any notice to the contrary; and

            (d) notwithstanding the foregoing, this Warrant may be sold,
transferred or assigned except pursuant to an effective registration statement
under the Securities Act or pursuant to an applicable exemption therefrom.

      12. REGISTRATION RIGHTS. The Company is obligated to register the shares
of Common Stock issuable upon exercise of this Warrant in accordance with the
terms of the Registration Rights Agreement.

      13. WARRANT REDEMPTION. Upon occurrence of the events described in
Sections 3.4 and 10.4(c) of the Purchase Agreement, the Company, at the request
of Holder, shall redeem all outstanding Warrants that remain unexercised at a
redemption price equal to the greater of (x) an appraised value of the Warrants,
as determined by Black Sholes, on the date they are called for redemption and
(y) the number of Warrants being redeemed multiplied by the excess of (A) the
average Closing Bid Price of the Common Stock for the five Trading Days
immediately prior to the date that the Warrants are called for redemption over
(B) the exercise price of the Warrants.

      14. NOTICES, ETC.. All notices and other communications from the Company
to the Holder of this Warrant shall be mailed by first class registered or
certified mail, postage prepaid, at such address as may have been furnished to
the Company in writing by such Holder or, until any such Holder furnishes to the
Company any address, then to, and at the address of, the last Holder of this
Warrant who has so furnished an address to the Company.

      15. MISCELLANEOUS. This Warrant and any term hereof may be changed,
waived, discharged or terminated only by an instrument in writing signed by the
party against which enforcement of such change, waiver, discharge or termination
is sought. This Warrant shall be construed and enforced in accordance with and
governed by the internal laws of the State of Georgia. The headings in this
Warrant are for the purposes of reference only, and shall not limit or otherwise
affect any of the terms hereof. The invalidity or unenforceability of any
provision hereof shall in no way affect the validity or enforceability of any
other provision.


                            [SIGNATURE PAGE FOLLOWS]


                                      150
<PAGE>

      DATED as of September 15, 2000.


                                           eMISSIONS TESTING, Inc.


                                           By: /s/ William S. Estroff
                                              ----------------------------------
                                              Name: William S. Estroff
                                              ----------------------------------
                                              Title: President
                                                    ----------------------------

[Corporate Seal]


Attest:

By:
   -----------------------------------------
         Secretary


                                      151
<PAGE>

                                    EXHIBIT A

                        FORM OF NOTICE EXERCISE - WARRANT
                       (To be executed only upon exercise
                       of the Warrant in whole or in part)

To ____________________________________________

      The undersigned registered Holder of the accompanying Warrant, hereby
exercises such Warrant or portion thereof for, and purchases thereunder,
__________(2) shares of Common Stock (as defined in such Warrant) and herewith
makes payment therefor in the amount and manner set forth below, as of the date
written below. The undersigned requests that the certificates for such shares of
Common Stock be issued in the name of, and delivered to, whose address is
________________________________________.

      The Exercise Price is paid as follows:

      |_| Bank draft payable to the Company in the amount of $_____________.
      |_| Wire transfer to the account of the Company in the amount of $_______.

      Upon exercise pursuant to this Notice of Exercise, the Holder will be in
compliance with the Limitation on Exercise (as defined in the Securities
Purchase Agreement pursuant to which this Warrant was issued).

Date:
     ------------------------------   --------------------------------------
                                      (Name must conform to name of Holder as
                                      specified on the face of the Warrant)


                                      By:
                                         --------------------------------------
                                         Name:
                                              ---------------------------------
                                         Title:
                                               ---------------------------------

                                      Address of Holder:
                                                        ------------------------

                                                     ---------------------------

                                                        ------------------------
 Date of exercise:
                  ------------------

----------

      (2)Insert the number of shares of Common Stock as to which the
accompanying Warrant is being exercised. In the case of a partial exercise, a
new Warrant or Warrants will be issued and delivered, representing the
unexercised portion of the accompanying Warrant, to the Holder surrendering the
same.


                                      152
<PAGE>
                                    ANNEX B

                             WARRANT EXERCISE LEDGER
<TABLE>
<CAPTION>

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                 ORIGINAL NUMBER OF      WARRANTS      EXERCISE PRICE      NEW BALANCE         ISSUER         HOLDER
    DATE              WARRANTS           EXERCISED         PAID            OF WARRANTS        INITIALS       INITIALS
----------------------------------------------------------------------------------------------------------------------
<S>              <C>                     <C>           <C>                 <C>                <C>            <C>
----------------------------------------------------------------------------------------------------------------------

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</TABLE>


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