Technical tool to evaluate the effectiveness of control measures I. ALLEGRINI and C. PERRINO Consiglio Nazionale delle Ricerche ISTITUTO sull’INQUINAMENTO ATMOSFERICO Via Salaria km 29,300 - C.P Monterotondo Stazione - ROMA Reducing the Impact of Vehicles on Air and Environment Quality in Cities – Mexico City Jan , 2004

PRESENTATION OUTLINE  Effectiveness of control measures  Meteorology-Concentration relationship  Evolution of the Boundary layer  Examples

Parameters acting on M:  Emission fluxes  Physico-chemical transformations  Deposition

Parameters acting on V:  Advection (mainly horizontal movements of the air masses, due to winds)  Convection (mainly vertical movements due to the heating of the lower air masses

Concentration variations for a pollutant i

Low-reactivity primary pollutants: are negligible

Radon: can be regarded as constant

Low-reactivity primary pollutants: Radon:

ATMOSPHERIC STABILITY MONITOR

Temporal pattern of natural radioactivity in Rome

EMISSIONE DI RADON The mixing of the lower atmospheric layers is reduced: the dilution of Radon is hampered and its air concentration increases. The lower atmospheric layers are well mixed: the Radon emitted from the ground dilutes and its air concentration is almost constant.

During warm months natural radioactivity shows a well-defined and modulated temporal pattern (all days are similar: nocturnal stability and convective mixing during the day) During cold months high-pressure periods are sporadic and advection often occurs. Diurnal mixing is weak and of limited duration.

The simplest air pollution model 2 maxima at about 6-7 am and 6-7 pm

SUMMER: when the morning traffic increases the lower atmopshere is already well-mixed; night time stability occurs when the traffic has already decreased. WINTER: when the morning traffic increases the mixing layer is still undeveloped; evening stability occurs when the traffic flow is still high. PRIMARY POLLUTION EPISODES

December 1 st : nocturnal stability and daytime mixing - CO shows a distinct 2-peak shape December 2 nd : weak daytime mixing – CO keeps high values during the whole day December 3 rd : intermediate conditions December 4 th (from noon) and 5 th : advection – CO keeps low values during the whole day

Atmospheric stability and Oxidants NO + O NO Tot. Ox = Constant 23 Ox rome

DAY BEFORE THE EPHIPHANY HOLIDAY The Atmospheric Stability Index (two scalars referring to morning and to evening hours) is calculated on the basis of natural radioactivity values and of their time derivatives during significant periods of the day. Primary pollution events are closely dependent on the mixing conditions of the lower atmopsheric layers, well described by the ASI

COMBINED ATMOSPHERIC STABILITY INDEX: 1-YEAR RESULTS

A one-to-one correlation is not expected since the ASI takes into account only one of the two driving forces determining pollutant concentrations, that is the meteorological factor. The two data sets should coincide only if the emission flux of benzene were constant in time

SCATTER PLOT OF THE MORNING ATMOSPHERIC STABILITY INDEX AND THE MORNING BENZENE AVERAGE CONCENTRATION: THE DATA GROUPS ON THREE DIFFERENT SECTION OF THE PLANE ACCORDING TO THE DIFFERENT INTENSITY OF THE TRAFFIC DURING WEEKDAYS, SATURDAYS AND SUNDAYS

On August, the benzene air concentration was lower than predictable on the only basis of the mixing properties of the atmopshere because the emission flux was distinctly lower than during the rest of the year.

Classification of the days of one year according to the ASI (probability of a primary pollution event) and according to the real benzene concentration.

BENZENE

USE OF THE ATMOSPHERIC STABILITY INDEX FOR THE EVALUATION OF POLLUTION TRENDS OVER THE YEARS IN THE PRESENCE OF SIMILAR ATMOSPHERIC CONDITIONS, WE OBSERVE A DECREASE OF BENZENE AIR CONCENTRATION WE CAN CONCLUDE THAT THIS IS DUE TO A REAL DECREASE IN THE EMISSION FLUXES INSIDE THE URBAN AREA

CONCLUSIONS: Natural radioactivity is a valuable tool for the interpretation of atmospheric pollution. The Atmospheric Stability Indexes allow the characterisation of the period under study in terms of meteorological predisposition to a primary pollution event. The ASI allow public Authorities to evaluate, on a scientific basis, the results of possible strategies or actions undertaken to reduce urban pollution. The ASI make it possible to carry our a sound comparison of pollutant concentration trend over the years.