CO Editor

Suggestions for revision or reasons for rejection

The authors have spent an impressive amount of effort to improve the manuscript, and the study represents an important contribution to the assessment of pollutant emissions from ship traffic. I feel that the paper is ready for publication, except for the improper usage of variable names in equations, which I have already commented in my first review. The usage of variable names needs to be revised according to the IUPAC guidelines prior to the publication in ACP.
I appreciate very much that the authors have done a survey, where they find that multi-letter variables are used in numerous publications. The usage of mathematical symbols is not a democratic decision, and this survey rather indicates that general rules for the usage of symbols and quantities in mathematical equations seem to be ignored by a growing number of scientists.
According to the AMT manuscript preparation guidelines, the IUPAC recommendations need to be followed, which state that “A clear distinction should be drawn between the names and symbols for physical quantities, and the names and symbols for units. […] The symbol for a physical quantity should be a single letter of the Latin or Greek alphabet. Capital or lower case letters may both be used. The letter should be printed in italic (sloping) type. When necessary the symbol may be modified by subscripts and superscripts of specified meaning. Subscripts and superscripts that are themselves symbols for physical quantities or for numbers should be printed in italic type; other subscripts and superscripts should be printed in Roman (upright) type.”
The naming of variables is thus not a “matter of personal taste”, as the authors state in their reply to my comments, but follows strict conventions. It needs to be clearly distinguished between the name of a physical quantity (“slant column density”), its abbreviation (“SCD”) and the according mathematical symbol (e.g., “S”). The term “SCD” in an equation thus represents the product of three quantities, namely S times C times D. Certainly, variable names such as “RESIDUAL” used in the manuscript are inappropriate.

Interactive discussion

Peer-review completion