Dear Authors,

There are still too many repetitive materials in the abstract and it lacks of concise statements. Please use the following abstract (add one or two sentences at the end of the abstract summarizing the results of CH4 and CO2 co-variability, not just stating what you have done):


To investigate temporal variability of methane (CH4) fluxes in an urban environment, air-surface exchange fluxes of CH4 were continuously measured using eddy covariance technique at a city-centre site in Łódź, Poland during July 2013 to August 2015. In the immediate vicinity of the measurement site, potential methane sources include vehicle traffic, dense sewerage infrastructure and natural gas networks. Sensible and latent heat fluxes have also been measured since 2000 and carbon dioxide fluxes since 2007 at this site. Upward CH4 fluxes dominated during the measurement period, indicating the city centre being a net source of CH4 to the troposphere. The highest monthly fluxes were observed in winter (2.0 to 2.7 g·m-2·month-1) and the lowest in summer (0.8 to 1.0 g·m-2·month-1). Fluxes on working days were around 6% higher than on weekends. The cumulative flux indicates that the city centre emitted a net quantity of nearly 18 g·m-2 of CH4 in 2014.


Please also consider the following concerns:
Page 1: Line 21-22, are the numbers here for individual samples, or for hourly, daily, monthly or seasonal average values?

Page 1, Lines 25-26: here you used unit “month-1”, while in the paper (Page 10, line 31-32), monthly average flux used unit “s-1”. You should use consistent units when discussing the same thing.