Analysis of the joint occurrence of extreme heat events and particulate matter increases in Bologna

Warm spells (WS) are defined as prolonged periods of temperatures above a threshold defined by climatology for a certain location. A WS occurring during the warm season is called heat wave. Many studies have identified an association of those events with concurrent increases in tropospheric ozone concentrations, but only few have investigated the association of WS with increasing particulate matter (PM) concentrations. This thesis aims to analyse this connection. This study has been carried out in the city of Bologna (44° 29' 38'' N, 11° 20' 35'' E) in the period between 1st January 2023 and 30th November 2023. The indexes Warm Spell Duration Index and Excess Heat Factor have been utilized to identify WS. PM exceedances have been identified through an index based on the variability of PM exploiting the 80th percentile of the seasonal distributions as threshold. Seven joint events of WS and PM increases have been identified during the investigated period: two during winter, three during summer and two during autumn. The event occurred between 11th and 20th July 2023 has been characterised in detail from the synoptic, physical and chemical points of view, employing data from in situ instruments or online open data. A synoptic pattern has encouraged the transport of desertic PM from Algeria towards Italy and the concurrent presence of WS through the African anticyclone. The analysis of the PM size distribution has highlighted a general increase in particle number concentrations for all sizes. The chemical analysis of PM composition has supported the identification of the arrival of air masses from the Sahara Desert to the study site. This research has defined a methodological study for the analysis of joint WS and PM increases showing a method for their identification. The in-depth analysis conducted for the July 2023 event have elucidated the role of the synoptic pattern with respect to WS and desertic PM transport to the study area.