MOCRA: a Monte Carlo code for the simulation of radiative transfer in the atmosphere.

This paper describes the radiative transfer model (RTM) MOCRA (MOnte Carlo Radiance Analysis), developed in the frame of DOAS (Differential Optical Absorption Spectroscopy) to correctly interpret remote sensing measurements of trace gas amounts in the atmosphere through the calculation of the Air Mass Factor. Besides the DOAS-related quantities, the MOCRA code yields: 1- the atmospheric transmittance in the vertical and sun directions, 2- the direct and global irradiance, 3- the single- and multiple- scattered radiance for a detector with assigned position, line of sight and field of view. Sample calculations of the main radiometric quantities calculated with MOCRA are presented and compared with the output of another RTM (MODTRAN4). A further comparison is presented between the NO2 slant column densities (SCDs) measured with DOAS at Evora (Portugal) and the ones simulated with MOCRA. Both comparisons (MOCRA-MODTRAN4 and MOCRA-observations) gave more than satisfactory results, and overall make MOCRA a versatile tool for atmospheric radiative transfer simulations and interpretation of remote sensing measurements

Observations of tropospheric compounds at Evora station with multi-axis hyper spectral measurements

The multi purpose UV-Vis. Spectrometer for Atmospheric Tracers Measurement (SPATRAM) is installed at the Observatory of the Geophysics Centre of Evora (38.5º N, 7.9º W) - Portugal, since 2004, measuring the zenith scattered radiation in the 300-550 nm spectral range. The main products are the total column and the vertical profiles of NO2 and O3 obtained with the application of the Differential Optical Absorption Spectroscopy (DOAS) algorithms and with inversion schemes based on the Optimal Estimation methods respectively. Recently (February 2009), the MIGE (Multiple Input Geometry Equipment) was coupled to the SPATRAM instrument allowing for the measurements of the diffused radiation in directions away from the zenith one (Off-Axis). MIGE is an alt-azimuth platform based on a very simple optical layout, using an optical fibre to transmit the radiation inside the monochromator of the SPATRAM equipment. Thanks to the solution adopted in the developing phase, MIGE is able to scan the whole hemisphere. In this work, after a brief description of the MIGE, the first and preliminary results for vertical profiles of NO2 in the Planetary Boundary Layer (PBL), and the values of Slant Column Densities (SCD) of O3 and SO2 measured in Off-Axis configuration at Evora Station, are presented and discussed

Influence of in-port ships emissions to gaseous atmospheric pollutants and to particulate matter of different sizes in a Mediterranean harbour in Italy

Ship emissions are a growing concern, especially in coastal areas, for potential impacts on human health and climate. International mitigation strategies to curb these emission, based on low-sulphur content fuels, have proven useful to improve local air quality. However, the effect on climate forcing is less obvious. Detailed information on the influence of shipping to particles of different sizes is needed to investigate air quality and climate interaction. In this work, the contributions of maritime emissions to atmospheric concentrations of gaseous pollutants (NO, NO2, SO2, and O-3) and of particles (sizes from 0.009 mu m to 30 mu m) were investigated considering manoeuvring (arrival and departure of ships) and hotelling phases (including loading/unloading activities). Results showed that the size distributions of shipping contributions were different for the two phases and could be efficiently described, using measured data, considering four size-ranges. The largest contribution to particles concentration was observed for D-p < 0.25 mu m, however, a secondary maximum was observed at D-p = 0.35 mu m. The minimum contribution was observed at D-p around 0.8-0.9 mu m with a negligible contribution from hotelling for size range 0.4-1 mu m. The comparison of 2012 and 2014 datasets showed no significant changes of gaseous and particulate pollutant emissions and of the contribution to particle mass concentration. However, an increase of the contribution to particle number concentration (PNC) was observed. Results suggested that harbour logistic has a relevant role in determining the total impact of shipping on air quality of the nearby coastal areas. Additionally, future policies should focus on PNC that represents an important fraction of emissions also for low-sulphur fuels. DOAS remote sensing proved a useful tool to directly measure NO2 and SO2 ship emissions giving estimates comparable with those of emission inventory approach