The Atmospheric Deposition of Polycyclic Aromatic Hydrocarbons in the Metropolitan City of Rome in the Year 2022/2023

Abstract

The measurement of atmospheric deposition fluxes is an excellent tool for assessing the contamination of territory and the subsequent exposure of the population to major contaminants through the food chain. In this context, the aim of this study was to measure the polycyclic aromatic hydrocarbon (PAH) deposition fluxes in the city of Rome (ISS Station) during the year 2022/2023 at two different heights above the ground (vertical profile), in order to evaluate the influence that the vertical profile has on PAH deposition. Two measuring positions were identified, one at street level and one at a height of 20 m. The collection of bulk atmospheric depositions was carried out approximately every 30 days, and the PAHs were determined according to the indications given in ISTISAN Report 06/38 and Standard UNI EN 15980:2011. The results show that throughout the year, the deposition rates of settleable dust were always higher at the lower (annual average of 48.5 mg m⁻² day⁻¹) collection position than at the higher position (annual average of 17.5 mg m⁻² day⁻¹). Despite this difference, the concentrations and profiles of the main PAHs analyzed, as indicated in EU Directive 2024/2881, in the dust collected at the two positions were almost similar, showing that the vertical profile did not influence the composition and concentration of PAHs in the collected settleable dust. Furthermore, a comparison of the deposition rates of sedimentable dust and PAHs with the legislative references currently present in Europe was made, highlighting that in the city of Rome during the monitoring period of this study, the values of dust and PAHs were lower than the limit and guide values and were also in line with other Italian urban locations.

1. Introduction

The determination of total or bulk atmospheric deposition is one of the key elements of the strategy to assess population exposure to organic and inorganic micropollutants through the ingestion of contaminated foodstuffs [1,2]. The European Union, through EU Directive 2024/2881 [3], defines total atmospheric deposition as “the total mass of pollutants that is transferred from the atmosphere to surfaces (e.g., soil, vegetation, water, buildings, etc.) in a given area within a given time period”. Total or “bulk” deposition, BD, is the sum of dry and wet deposition. Wet deposition is the process of transferring pollutants from the atmosphere to the ground through one of several forms of precipitation (rain, snow or fog), while dry deposition refers to the transfer of sedimentable particulate material (SPM) to the ground under the action of gravity [4]. Among the micropollutants to be determined for BD are seven polycyclic aromatic hydrocarbons (PAHs) of hygienic health interest, in particular, benzo[a]pyrene (included in Group 1, “Carcinogenic to humans”, by the International Agency for Research on Cancer (IARC)), benzo[a]anthracene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, dibenzo[a,h]anthracene and indeno [1,2,3-cd]pyrene (included in Group 2B, “Possibly carcinogenic to humans”, by the IARC). PAHs, once deposited on the soil, tend to pass through and accumulate in vegetation, agricultural crops, fodder and consequently in animals, exposing the population to them through the consumption of contaminated foodstuffs, especially dairy products, meat and vegetables [5]. Several studies have been conducted in Europe and Italy on the BD monitoring of organic and inorganic micropollutants [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. Some of these studies have shown that forage, grass silage and soil are contaminated through the deposition of SPM, with which persistent organic pollutants, including PAHs, are associated [5,23]. For this reason, it is important to monitor BD, especially in areas where industrial activities are present, such as refineries, metallurgical industries, large combustion plants (LCPs), chemical plants, cement factories, biomass plants and incinerators, in order to assess the accumulation of PAHs in the soil and the possible effects on human health. It is therefore crucial in monitoring strategies to develop atmospheric deposition detection plans to determine both the quantity of BD (in terms of deposition fluxes) and the chemical composition [1]. It should be underlined that there is currently no legislation on BD in Europe and Italy, as well as that no guideline values have been indicated. Despite these considerations, several countries in Europe have adopted their own laws, setting limit values for BD [24,25,26,27,28,29,30,31]. For instance, for PAHs, Germany has set an annual average deposition limit value for benzo[a]pyrene (BaP) of 500 ng m⁻² d⁻¹ [32]. Currently, the European Commission, through a new air quality Directive, requires member states to increase their BD monitoring activities in order to obtain sufficient data for the establishment of shared limits and guideline values [3]. There are not many publications in the literature on the monitoring of the atmospheric deposition of PAHs. In Italy, BD activities have been conducted mainly by the Italian National Institute of Health and the Regional Agencies for Environmental Protection (ARPA). None of the work on BD in the literature studies the effect that the vertical profile has on the deposition of PAHs and, in particular, BaP. In this study, the authors show how the deposition of SPM and PAH varies at two different heights above the ground. This approach can be extremely useful in atmospheric deposition monitoring plans in order to understand whether it is appropriate to monitor BD at different heights in the study area. Based on the authors’ knowledge, this is the first paper that addresses this important issue in the metropolitan area of Rome. In addition, this study aims to provide data on the deposition of PAHs in the metropolitan city of Rome, also in view of the transposition and application of the new EU Directive, to increasingly protect citizens’ health.

2. Materials and Methods

BD monitoring activities were conducted at the Italian National Institute of Health (ISS) in Viale Regina Elena 299 (REL) in Rome. This site can be classified as an urban area, where the main emission sources are represented by exhaust fumes from cars–buses and natural gas centralized domestic heating systems during the winter season (from 15 November to 15 March). Throughout the city during the summer, there is a recurring presence of open fires at landfill sites, which, depending on wind direction and weather conditions, may contribute to the load of pollutants in BD. The two BD locations were identified taking into account the characteristics of the area, distributed between different heights from the road (vertical profile). Station 1 (REL 1) is located at the ISS air pollutant monitoring station at street level, at a distance of approximately 10 m from Station 2 (REL 2), which is located on the terrace of the building, 20 m higher than REL 1, based on the vertical profile. Figure 1 shows the two sampling stations.

A deposimeter for BD sampling was positioned at the two stations, following the indications given in ISTISAN Report 06/38 [33], subsequently reported in UNI EN 15980:2011 and in Legislative Decree no. 155/2010 [34,35]. The deposimeter for the collection of PAHs in BD consists of a “bottle+cylindrical funnel” system in Pyrex^® glass, with a wet deposition collection capacity of 10 liters. The area of the cylindrical collection funnel at the top of the bottle is 0.0363 m². BD sampling lasted a full year, as indicated by the European standard, and started in March 2022 and ended in April 2023. The deposimeter was replaced approximately every 30 days. In

Table 1. Sampling period and days of exposure for BD at REL 1 and REL 2.

REL 1		REL 2
Sampling Period (Prevalent Month)	Days of Exposure	Sampling Period (Prevalent Month)	Days of Exposure
02/03/22–06/04/22 (March 2022)	36	01/03/22–06/04/22 (March 2022)	37
06/04/22–06/05/22 (April 2022)	30	06/04/22–06/05/22 (April 2022)	30
06/05/22–09/06/22 (May 2022)	33	06/05/22–09/06/22 (May 2022)	33
09/06/22–05/07/22 (June 2022)	25	09/06/22–05/07/22 (June 2022)	25
05/07/22–04/08/22 (July 2022)	29	05/07/22–04/08/22 (July 2022)	29
04/08/22–05/09/22 (August 2022)	31	04/08/22–05/09/22 (August 2022)	31
05/09/22–04/10/22 (September 2022)	29	05/09/22–05/10/22 (September 2022)	30
04/10/22–10/11/22 (October 2022)	37	05/10/22–10/11/22 (October 2022)	36
10/11/22–15/12/22 (November 2022)	35	10/11/22–15/12/22 (November 2022)	35
15/12/22–16/01/23 (December 2022)	32	15/12/22–16/01/23 (December 2022)	32
16/01/23–16/02/23 (January 2023)	30	16/01/23–16/02/23 (January 2023)	30
16/02/23–13/03/23 (February 2023)	26	16/02/23–13/03/23 (February 2023)	26
13/03/23–13/04/23 (March 2023)	31	13/03/23–13/04/23 (March 2023)	31

, the sampling start and end dates along with the days of deposimeter exposure are summarized.

At the end of each sampling event, the bottle and cylindrical funnel were treated separately. With regard to the funnel, the inner walls were rinsed with ultra-pure acetone in order to remove condensation water and then were wiped with degreased cotton wool to recover the dry deposition adhered to the walls. The acetone wash and cotton wool were stored away from light for later extraction. Before filtration, 100 μL of benzo[a]pyrene-d₁₂ solution at 5 ng mL⁻¹ was added to the bottle [33]. This standard was used to evaluate the percentage recovery of PAHs from the entire extraction process. The wet deposition collected in the bottle was vacuum-filtered through a 47 mm diameter and 1 μm porosity glass fiber filter without organic binders, which is suitable for PAH analysis in BD as indicated in UNI EN 15980:2011 [34]. The filter was previously conditioned under a constant weight in a climate chamber at a controlled temperature and humidity for at least 48 h (20 °C and 50% R.H). After filtration, the same filter was placed under the same conditions for the same length of time. SPM was calculated gravimetrically and expressed as mg/m² per day of exposure. The extraction of PAHs from SPM collected on the filter and from wet deposition was conducted using dichloromethane (DCM) as a solvent, in an ultrasonic bath and in a separating funnel, respectively. Acetone wash and cotton wool were extracted with DCM by liquid–liquid and ultrasound extraction, respectively. The extraction process was repeated three times, and the DCM was recovered in a collecting flask. All extracts were combined into one extract, which was concentrated by a rotary evaporator to about 2 mL and passed over an anhydrous sodium sulphate column previously dried overnight to remove residual water. The final extract was then transferred to a 5 mL conical bottom vial and concentrated to 100 μL through a gentle flow of purified nitrogen (N₂). Instrumental analysis was carried out by means of a Gas Chromatograph (mod. GC-6890) coupled with a single-quadrupole mass spectrometer (mod. MSD-5973). The acquisition of the instrumental signal was carried out through single-ion monitoring (SIM).

Table 2. Target ion (T1), secondary ion 1 (S1) and secondary ion 2 (S2) for each PAH under study with the respective LOD as ng m⁻² d⁻¹. Repeatability and reproducibility as intra-day and inter-day values (RSD%) for each PAH.

PAH	Target Ion (T1)	Secondary Ion 1 (S1)	Secondary Ion 2 (S2)	LOD (ng m−2 d−1)	Intra-Day (RSD%)	Inter-Day (RSD%)
Benzo[a]Anthracene (BaA)	228	229	114	0.5	2.1	5.0
Chrysene (CHR)	228	229	114	1	5.1	7.2
Benzo[a]Pyrene (BaP)	252	253	126	0.5	5.5	7.3
Benzo[b]Fluoranthene (BbFA)	252	253	126	1	4.2	7.5
Benzo[j]Fluoranthene (BjFA)	252	253	126	1	4.9	8.0
Benzo[k]Fluoranthene (BkFA)	252	253	126	1	5.2	7.7
Dibenzo[a,h]Anthracene (DBahA)	278	279	139	3	4.9	8.6
Indeno [1,2,3-cd]Pyrene (INP)	276	277	138	1	6.1	7.0

shows the PAHs determined in the BD in this study, which were identified in EU Directive 2024/2881 [3]. Furthermore, the characteristic fragments (m/z) of each PAH that was set for acquisition through SIM and the respective detection limits (LODs) are also reported. LODs were calculated as the analyte concentration, yielding a signal equal to the mean signal of n replicate blank measurements (in this study, 10 measurements; n = 10) plus three times the standard deviation of these measurements. The linear dynamic range (LDR) was from 0.01 to 5 μg mL⁻¹. In addition, the repeatability and reproducibility values of the method were calculated by evaluating the recoveries through adding a known amount of a PAH mix solution to sample blanks and calculated as percentage relative standard deviation (RSD%).

With reference to data below the detection limit (unrevealable data = NR), the authors used the ISTISAN Report 04/15 approach [36]. All NR values were replaced by the numerical value LOD/2. This approach can be defined as precautionary from a hygienic–sanitary point of view. The Statistical Software Package for Windows SPSS Inc., Chicago, IL, USA, was used for statistical analysis. Statistical significance was attributed to p values < 0.05 and was obtained using a “t-test”.

3. Results and Discussion

In the following section, the BD values of SPM and PAHs at REL 1 and REL 2 will be shown. Subsequently, the correlations between SPM and PAHs at both locations and the profiles of the various PAHs will be shown in order to identify the main emission sources. The PAH concentration trends during the four seasons will also be discussed, and finally, the authors will devote a paragraph to comparing the data from this study with data available in the literature from other Italian locations.

3.1. SPM Deposition Rates

Average seasonal SPM ground deposition rates measured at the two locations are shown in

Table 3. Average seasonal SPM deposition rates (mg m⁻² d⁻¹) at REL 1 and REL 2.

Season	SPM (mg m−2 d−1)
	REL 1	REL 2
Spring	30	10
Summer	96	34
Autumn	41	19
Winter	27	7
Annual average	48.5	17.5

. Figure 2 shows the SPM trend during the entire sampling year. The monthly SPM values at the two locations are given in Table S1 of the Supplementary Materials.

3.2. PAH Deposition Rates

The monthly and annual average deposition fluxes of the PAHs considered in this study are shown in

Table 4. Monthly and annual PAH deposition rates in ng m⁻² d⁻¹ at REL 1 and REL 2 with respective standard deviations (n = 3).

Sampling Period	Station	BaA	CHR	B[b+j+k]FA	BaP	DBahA	INP	Total PAHs
		(ng m−2 d−1)
March 2022	REL 1	5.8 ± 0.1	4.2 ± 0.2	12.7 ± 1.1	4.0 ± 0.1	1.5 ± 0.0	2.3 ± 0.0	30.5 ± 1.5
	REL 2	1.2 ± 0.1	1.0 ± 0.0	3.9 ± 0.3	1.1 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	9.2 ± 0.4
April 2022	REL 1	7.7 ± 0.5	5.0 ± 0.2	10.3 ± 0.7	3.7 ± 0.2	1.5 ± 0.0	0.5 ± 0.0	28.6 ± 1.6
	REL 2	2.5 ± 0.1	1.6 ± 0.0	3.3 ± 0.2	1.2 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	10.6 ± 0.3
May 2022	REL 1	1.4 ± 0.0	0.5 ± 0.0	3.8 ± 0.4	1.7 ± 0.1	1.5 ± 0.0	0.5 ± 0.0	9.3 ± 0.5
	REL 2	0.3 ± 0.0	0.5 ± 0.0	0.5 ± 0.0	0.3 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	3.5 ± 0.0
June 2022	REL 1	0.3 ± 0.0	0.5 ± 0.0	0.5 ± 0.0	0.3 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	3.5 ± 0.0
	REL 2	0.3 ± 0.0	0.5 ± 0.0	0.5 ± 0.0	0.3 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	3.5 ± 0.0
July 2022	REL 1	3.3 ± 0.2	0.5 ± 0.0	6.0 ± 0.4	2.9 ± 0.1	1.5 ± 0.0	0.5 ± 0.0	14.6 ± 0.7
	REL 2	0.6 ± 0.0	0.5 ± 0.0	1.1 ± 0.1	0.5 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	4.8 ± 0.1
August 2022	REL 1	2.3 ± 0.1	0.5 ± 0.0	4.4 ± 0.9	2.2 ± 0.1	1.5 ± 0.0	0.5 ± 0.0	11.4 ± 1.1
	REL 2	1.4 ± 0.2	0.5 ± 0.0	2.6 ± 0.3	1.3 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	7.8 ± 0.5
September 2022	REL 1	0.3 ± 0.0	0.5 ± 0.0	0.5 ± 0.0	1.2 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	4.4 ± 0.0
	REL 2	0.3 ± 0.0	0.5 ± 0.0	0.5 ± 0.0	0.3 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	3.5 ± 0.0
October 2022	REL 1	0.3 ± 0.0	0.5 ± 0.0	0.5 ± 0.0	0.3 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	3.5 ± 0.0
	REL 2	0.3 ± 0.0	0.5 ± 0.0	0.5 ± 0.0	0.3 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	3.5 ± 0.0
November 2022	REL 1	4.6 ± 0.5	5.7 ± 0.6	14.3 ± 1.0	5.2 ± 0.3	1.5 ± 0.0	1.2 ± 0.0	32.5 ± 2.4
	REL 2	0.9 ± 0.0	1.1 ± 0.0	2.4 ± 0.2	0.9 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	7.2 ± 0.2
December 2022	REL 1	9.8 ± 0.8	13.6 ± 1.1	19.8 ± 2.3	7.3 ± 1.5	1.5 ± 0.0	3.0 ± 0.2	55.0 ± 5.9
	REL 2	1.0 ± 0.0	1.1 ± 0.0	1.7 ± 0.1	1.7 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	7.4 ± 0.1
January 2023	REL 1	4.4 ± 0.6	5.1 ± 0.5	10.6 ± 1.0	4.3 ± 0.2	1.5 ± 0.0	2.8 ± 0.0	28.7 ± 2.3
	REL 2	2.0 ± 0.0	2.0 ± 0.2	4.9 ± 0.5	2.0 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	12.8 ± 0.7
February 2023	REL 1	5.4 ± 0.4	4.5 ± 0.1	11.2 ± 0.9	2.8 ± 0.1	1.5 ± 0.0	4.0 ± 0.2	29.4 ± 1.7
	REL 2	2.1 ± 0.1	2.1 ± 0.2	5.6 ± 0.5	1.3 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	13.2 ± 0.8
March 2023	REL 1	1.3 ± 0.0	1.8 ± 0.1	3.9 ± 0.2	3.4 ± 0.2	1.5 ± 0.0	2.0 ± 0.0	13.9 ± 0.5
	REL 2	0.3 ± 0.0	0.5 ± 0.0	0.5 ± 0.0	0.9 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	4.1 ± 0.0
Annual average	REL 1	3.6 ± 0.2	3.3 ± 0.2	7.6 ± 0.7	3.0 ± 0.2	1.5 ± 0.0	1.5 ± 0.0	20.4 ± 1.3
	REL 2	1.0 ± 0.0	1.0 ± 0.0	2.2 ± 0.2	0.9 ± 0.0	1.5 ± 0.0	0.5 ± 0.0	7.0 ± 0.2

.

The collection system used (bulk- or Bergerhoff-type deposimeter) made it possible to collect not only dry deposition but also wet deposition (rain) through the total collection system (bottle). The total SPM value includes the settleable particulate material that was present in the collected rain, which was filtered through a glass fiber filter, and the dust present in it remained on the filter. This collection system therefore allows for the simultaneous collection of dry and wet deposition, unlike, for example, systems that only allow for the collection of wet deposition (wet-only). In all seasons, the average SPM deposition fluxes were higher at REL 1, with the maximum value in the summer (96 mg m⁻² d⁻¹). This means that there was a greater contribution of SPM at REL 1 caused by SPM being deposited at road level due to human activities (mainly road transport and maintenance activities) [1,12,15]. SPM deposition was therefore greater during the hot and dry season than during the cold season (minimum value in winter of 7 mg m⁻² d⁻¹ at REL 2).

Figure 3 provides a better view of PAH deposition fluxes over the study period. It is evident that during the winter months (November 2022 to February 2023), total PAH deposition fluxes were higher due to the emission contribution from residential and non-residential heating systems. The highest recorded value was 55 ng m⁻² d⁻¹ in December at REL 1, and for BaP, the highest deposition fluxes were observed in November (5.2 ng m⁻² d⁻¹) and December (7.3 ng m⁻² d⁻¹), as well as at REL 1. Furthermore, during the cold season, the solar window and temperatures are reduced, and consequently, the possibility of PAH degradation is minimal compared to during the warm months [20]. In fact, with reference to the data and Figure 3, it can be observed that the summer months (June to October 2022) showed the lowest PAH deposition fluxes. The lowest values were for June, September and October, where all compounds were below the LOD. In any case, non-negligible PAH values were found in July and August 2022 due to the numerous fires that occurred both in the urban area of Rome and in suburban areas [37,38,39].

If attention is given only to the comparison of PAH deposition values between REL 1 and REL 2, higher levels at REL 1 are evident in all sampling months over the year. Actually, this is incorrect, because the SPM fluxes are significantly higher at REL 1 than at REL 2, so it should be necessary to normalize such data for related fluxes. For this purpose, the authors calculated the amounts of individual and total PAHs in the collected SPM, expressing the data in ng of PAHs per gram of SPM (ng g⁻¹). In accordance with this consideration,

Table 5. PAH concentrations in deposited dust (SPM) in ng g⁻¹ at REL 1 and REL 2.

Sampling Period	Station	BaA	CHR	B[b+j+k]FA	BaP	DBahA	INP	Total PAHs
		(ng g−1)
March 2022	REL 1	285	206	621	194	74 *	111	1418
	REL 2	308	256	1000	277	385 *	128 *	1841
April 2022	REL 1	324	210	431	153	63 *	21 *	1119
	REL 2	321	212	423	158	195 *	65 *	1114
May 2022	REL 1	31	11 *	82	37	33 *	11 *	150
	REL 2	13 *	26 *	26 *	13 *	77 *	26 *	-
June 2022	REL 1	3 *	5 *	5 *	3 *	15 *	5 *	-
	REL 2	12 *	25 *	25 *	12 *	74 *	25 *	-
July 2022	REL 1	42	6 *	77	37	19 *	6 *	156
	REL 2	44	34 *	76	36	103 *	34 *	156
August 2022	REL 1	21	4 *	40	20	13 *	4 *	80
	REL 2	20	7 *	39	20	22 *	7 *	78
September 2022	REL 1	3 *	6 *	6 *	15 *	19 *	6 *	-
	REL 2	5 *	11 *	11 *	5 *	33 *	11 *	-
October 2022	REL 1	10 *	19 *	19 *	10 *	58 *	19 *	-
	REL 2	27 *	55 *	55 *	27 *	164 *	55 *	-
November 2022	REL 1	271	336	842	309	89 *	71	1829
	REL 2	297	366	814	310	517 *	172 *	1786
December 2022	REL 1	236	326	476	174	36 *	72	1284
	REL 2	283	292	464	458	417 *	139 *	1497
January 2023	REL 1	580	670	1402	561	198 *	372	3586
	REL 2	548	554	1342	537	413 *	138 *	2981
February 2023	REL 1	166	137	345	85	46 *	123	856
	REL 2	140	137	368	87	98 *	33 *	731
March 2023	REL 1	49	67	147	126	56 *	76	467
	REL 2	50 *	101 *	101 *	177	302 *	101 *	-

* For compounds whose values are below the LOD, the approach reported in ISTISAN Report 04/15 was used.

shows the corrected calculated ratios, namely, the amounts of PAHs in the collected SPM at both locations. For compounds whose values are below the LOD, their contribution to the total PAH sum was not considered.

Following this approach, an important finding can be observed: the levels of PAHs present in the SPM collected at the two locations are quite similar and are not dependent on height; i.e., the vertical profile does not affect the total PAH composition and amount. The PAH profiles are definitively similar in the different seasons at both sampling sites, with differences related to the different sources being dependent on the effects of both anthropogenic activities and meteorological conditions, i.e., greater quantities during the winter season compared to the other seasons. This is explained by the fact that there is a higher deposition flux at REL 1 than at REL 2 and consequently a higher PAH flux, but the concentration of PAHs in the SPM collected at the two locations is almost identical. With this approach, the month with the highest PAH deposition in SPM is January 2023, with total PAH values of 3586 and 2981 ng g⁻¹ at REL 1 and REL 2, respectively. This is reliable as January is one of the coldest months in Rome, coming with the widespread use of domestic heating systems. With reference to July and August 2022, the concentrations of PAHs in SPM (156/156 and 80/78 ng g⁻¹ for July and August, at REL 1 and REL 2, respectively) at the two locations are almost equal, suggesting that the composition of SPM relative to PAHs is identical. Figure 4 shows the quantities of PAHs in SPM.

To evaluate the influence of the vertical profile on the quantities of PAHs present in the collected SPM, a Pearson correlation was conducted. The different SPM deposition fluxes at REL 1 and REL 2 and subsequently the quantities of PAHs in the dust were compared. Figure 5a shows the relationship between the SPM deposition fluxes at the two stations: a positive correlation is reported, with a correlation index r = 0.811 and a p-value = 0.00076. This indicates that the same variations in terms of SPM deposition tend to occur at the two locations. Consequently, the concentrations of PAHs in SPM measured at the two locations (data reported in Table 5) were studied (Figure 5b). Also, in this case, there is an extremely positive relationship (r = 0.968; p-value = 0.000077), indicating that the quantities of PAHs present in SPM are almost constant and do not vary between REL 1 and REL 2. In other words, the PAH composition and concentration present in SPM do not vary according to the vertical profile; i.e., altitude measurements do not affect PAH levels. The vertical profile therefore exclusively shows a quantitative difference in the collected SPM. In fact, during all months of sampling, higher SPM values were consistently recorded at REL 1 than at REL 2, with annual averages of 48.5 and 17.5 mg m⁻² d⁻¹, respectively. This means that the only difference between REL 1 and REL 2 is the absolute quantities of SPM collected and not the concentrations of PAHs.

3.3. Comparison of SPM and PAH Deposition Levels in Different Italian Locations

In Italy, several BD monitoring activities have been conducted in recent years to assess the contamination status of an area. These activities have been conducted mainly by the ISS and the Regional Agencies for Environmental Protection (ARPA). European and national legislation, unlike for suspended particulate matter (PM₁₀ and PM_2.5), does not indicate any limit or reference values for SPM and PAH deposition. Consequently, the studies carried out must be compared with reference or guideline values suggested in other European countries. In fact, several European countries over the years have enacted national laws in which limit values or guide values for SPM deposition are provided (

Table 6. Annual limit values of deposition rates for SPM (mg m⁻² d⁻¹) and BaP (ng m⁻² d⁻¹) in some European legislation.

European Country	SPM (mg m−2 d−1)	BaP (ng m−2 d−1)	References
Austria	210	-	[28]
Belgium	350 GV 650 *	-	[26]
Croatia	350	-	[27]
Germany	350 650 *	500	[24,25,32]
United Kingdom	200	-	[30]
Switzerland	200	-	[31]
Slovenia	200	-	[29]

GV: guide value; *: monthly limit.

). Recently, for the deposition of PAHs, only Germany has introduced a limit value to be complied with throughout the country, with only BaP values being limited (Table 6).

Table 7. Levels of BaP (ng m⁻² d⁻¹) and SPM (mg m⁻² d⁻¹) in other works at various locations in Italy and Germany.

Italian and German Locations (Regions)	Type of Locations	BaP (ng m−2 d−1)	SPM (mg m−2 d−1)	References
Aosta (Aosta Valley)	Urban	28	ns	[40]
Borgo Valsugana (Trento)	Urban	1–32	ns	[13]
Civitavecchia (Latium)	Industrial	1.4–4.6	27.3	[12]
	Urban	1.4–7.1	21.5
	Rural	1.4–3.9	27.9
La Spezia (Liguria)	Urban	0.8–1.0	88	[14]
Perugia (Umbria)	Urban	5–14	ns	[41]
Potenza (Basilicata)	Industrial	8.7–81.8	99.3	[42]
Rome (Latium)	Urban	3.6–4.1	21.5	[15]
San Nicola di Melfi (Basilicata)	Industrial	4.6–6.9	ns	[20]
	Urban	3.2–4.1
	Rural	1.9–5.7
Taranto (Apulia)	Industrial	123	720	[16]
	Urban	133	403
	Rural	6	32
Terni (Umbria)	Industrial	17	ns	[43]
	Urban	10
Venice (Veneto)	Urban	30	21.8	[18]
	Rural	6–9	31.1
Viggiano (Basilicata)	Industrial	1.3–4.5	31.4	[44]
Rome (Latium)	Urban	REL 1: 3.0	REL 1: 48.5	This study
		REL 2: 0.9	REL 2: 17.5
Southern Germany (Seebach, Lange Klinge and Waldstein)	Rural	4.4–31.8	ns	[45]
Bayreuth (Bavaria)	Rural	20.8	ns	[46]
Northeastern Bavaria	Rural	40.3–74.1	ns	[47]

ns: not specified.

shows the deposition values for SPM and BaP found through other research activities in Italy and Germany. It should be emphasized that none of the studies summarized in Table 7 and present in the literature have evaluated the influence of the vertical profile on SPM and PAH deposition. So, once again, this paper aimed to investigate such issues for the first time. BaP values are reported, as this is the only compound for which a reference value is established. Looking at the data, SPM deposition in this study is in line with the values found in other Italian locations, for both monitoring stations. With consideration of the lowest annual SPM deposition limits in Switzerland, Slovenia and the UK (200 mg m⁻² d⁻¹) (Table 6), the average annual SPM deposition ratios reported in this study are approximately four and eleven times lower for REL 1 and REL 2, respectively.

In [45,46,47], the BaP deposition values are well below the expected limit (500 ng m⁻² d⁻¹). It should be noted, however, that these monitoring activities were carried out in rural locations, where no appreciable emission sources are generally present. However, in both Germany and Italy, there is very scarce monitoring work on PAH in atmospheric deposition. Studies on PAH levels in BD and assessments of food hull contamination should be increased in light of the new recommendations in EU Directive 2024/2881.

It can be seen that the BaP annual average deposition fluxes measured in this study for both locations are in line with those measured in other Italian cities. Furthermore, in the absence of European and national regulatory limits, an assessment can be made by taking into account the maximum limit in Germany, which is 500 ng m⁻² d⁻¹. The BaP deposition flux values found at REL 1 and 2 are much lower than the German limit. The same consideration can be applied to the other locations shown in Table 7, where this limit is never exceeded. In any case, it must be specified that the reference value should only be a general indication, as these values are established on the basis of the characteristics of the national territory and the concentrations generally found in the environment. For this reason, monitoring activities of BaP deposition should be increased in Italy in order to have enough data to establish a guideline value to safeguard the health of the population exposed to pollutants through the ingestion of contaminated food.

4. Conclusions

The determination of atmospheric deposition is a fundamental tool for assessing the contribution of SPM to the contamination of land. In recent years, various PAH deposition monitoring activities have been carried out in Europe and in Italy, in urban and industrial areas. The main objective of the present study was both to provide data on PAH deposition fluxes in an urban environment in Rome (REL) and to assess the influence that the vertical profile has on the quali-quantitative composition of atmospheric deposition. The results show that dust deposition fluxes at the street-level location (REL 1) were always higher in quantity than at the elevated location (REL 2) throughout the year. However, the composition and quantities of BaA, CHR, BbFA, BjFA, BkFA, BaP, DBahA and INP in the collected dust were almost similar at the two stations. This was demonstrated by calculating the amount of each PAH in the collected SPM by expressing the data in nanograms of PAHs per gram of collected dust (ng g⁻¹). These data show that the vertical profile made no substantial difference in terms of the amount and composition of the PAHs present in the atmospheric depositions. At the same time, appreciable levels of some PAHs, including BaP, were observed during the summer months, leading the authors to hypothesize that the fires that occurred in the city may have contributed to the increase in deposition flows. The deposition fluxes measured at the two stations were always lower than the limit values identified in other European countries [24,25,26,27,28,29,30,31,32] for SPM and BaP. In Italy, limit values and/or guide values for BD atmospheric deposition and the related persistent organic pollutants (POPs) associated with it have not been established. In this regard, the authors, as already suggested [48], recommend that the scientific community pay greater attention to the issue of BD, providing data and support to the authorities in order to obtain limit values that indirectly protect the health of the population.