11 Apr 2023
 | 11 Apr 2023

Aerosol absorption by in-situ filter-based photometer and ground-based sun-photometer in an urban atmosphere

Alessandro Bigi, Giorgio Veratti, Elisabeth Andrews, Martine Collaud Coen, Lorenzo Guerrieri, Vera Bernardoni, Dario Massabò, Luca Ferrero, Sergio Teggi, and Grazia Ghermandi

Abstract. Light Absorbing Aerosols (LAA) are short-lived climate forcers with a significant impact on Earth radiative balance and include dust aerosols, Black Carbon (BC) and organic light-absorbing carbonaceous aerosol (collectively termed as Brown Carbon, BrC), which have been also proven to be highly toxic. Aerosol absorption at 5 wavelengths (UV, B, G, R, IR) by filter photometer was monitored continuously during two winter seasons in 2020 and 2021 in the city of Modena (South-central Po valley, Northern Italy) at the two regulatory air quality monitoring sites, along with other pollutants (PM10, PM2.5, O3, NO, NO2, C6H6) and vehicular traffic rate. Columnar levels of AOD and of other aerosol optical properties were concurrently monitored at multiple wavelengths by a local sun-photometer at urban background conditions and within the AERONET network. In-situ absorption levels were apportioned both to sources (fossil fuel, biomass burning) and to species (BC, BrC), while columnar absorption was apportioned to BC, BrC and mineral dust. The combined analysis of the atmospheric aerosol and gas levels and of the meteorological conditions (in-situ and by ERA5 reanalysis) identified the location of potential urban sources for BC and BrC, most likely traffic and biomass burning. In-situ data shown different diurnal/weekly patterns for BrC by biomass burning and BC by traffic, with minor differences among the background and the traffic urban conditions. AERONET version 3 Absorption Aerosol Optical Depth (AAOD) retrievals at 4 wavelengths allowed the estimate of the Absorptive Direct Radiative Effect by LAA over the same period under the reasonable assumption that the AOD signal is built up within the mixing layer. AERONET retrievals showed a modest correlation of columnar absorption with PBL-scaled in-situ observations, although the correlation improves significantly during a desert dust transport event, affecting both in-situ aerosol and columnar absorption, particularly in the Blue spectrum range. Low correlation occurred between the contribution of BrC to aerosol absorption for the in-situ and the columnar observations, with this contribution being generally larger at the former. Finally, evidences of a strongly layered atmosphere during the study period, featured by large spatial mixing and modest vertical mixing, were shown by ERA5-based atmospheric temperature profiles and by the large correlation of concurrent AERONET AOD retrievals in Modena and in Ispra (on the NW side of the Po valley, ca. 225 km distant from Modena).

Alessandro Bigi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-174', Anonymous Referee #1, 11 May 2023
  • RC2: 'Comment on egusphere-2023-174', Anonymous Referee #3, 09 Jun 2023

Alessandro Bigi et al.

Alessandro Bigi et al.


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Short summary
Atmospheric particles include compounds playing a key role on the greenhouse effect and on air toxicity. Concurrent observations of these compounds by multiple instruments are presented, following a deployment within an urban environment in the Po valley, one of the pollution hotspot of Europe. The study compares these data highlighting the impact by ground emissions, mainly vehicular traffic and biomass burning, on the absorption of Sun radiation and ultimately on climate change and air quality.