Evolution of size-segregated aerosol concentration in NW Spain: A two-step classification to identify new particle formation events.

Real-time measurements of particles in the 15-736 nm range have been obtained by a Scanning Mobility Particle Sizer to characterize the evolution of particle size distribution and new particle formation (NPF) events in an urban background area. The annual, weekly and diurnal variations of the modal (nucleation (Nnuc), Aitken (NAit) and accumulation (Nacc)) particle concentrations were characterised. The NAit and Nacc registered their maximums in cold months during rush hours, in the morning (0600-0900 UTC) and in the afternoon (1700-2000 UTC), while the maximums for Nnuc were reached in warm months during midday hours. NAit, Nacc and Ntotal showed a significant negative correlation with wind speed and a different relationship with the planetary boundary layer (PBL) height by periods. In the warm period, a positive significant correlation between PBL and Nnuc was registered, indicating that the higher dispersion promoted by a high PBL causes favourable conditions for the occurrence of NPF events (a low polluted atmosphere). NPF processes are one of the main sources of ultrafine particles (<100 nm) in the warm period. After a visual-based classification, 45 NPF events of type Ia (strong and with a good confidence level) were identified and analysed, occurring primarily between 1100 and 1500 UTC, mainly in spring and summer. In addition, a two-step method was developed for identifying NPF events: cluster analysis followed by discriminant analysis. The application of discriminant analysis to one of the clusters, grouping 93 days, enabled us to identify 55 of the 56 NPF events days included in the cluster. This method is a valuable tool for identifying NPF events quickly and effectively.

Scavenging of submicron aerosol particles in a suburban atmosphere: The raindrop size factor.

This paper studies the below-cloud scavenging caused by precipitation on ultrafine and accumulation modes, as well as the role of the different raindrop sizes in an urban environment. The equipment used to measure aerosol particles and raindrop variables includes a scanning mobility particle sizer spectrometer-SMPS and a Laser Precipitation Monitor (LPM), respectively. An analysis of the scavenging efficiency and the scavenging coefficient (λ) by modes and rain intensities was carried out. The main results observed have been: i) the nucleation (between 14 and 30 nm), Aitken (between 30 and 100 nm), accumulation 1 (between 100 and 300) and accumulation 2 (between 300 and 1000 nm) modes presented a scavenging efficiency of 15, 4, 22 and 21%, respectively; ii) events with rain intensities between 1 and 3 mm h-1 caused less scavenging in all modes; iii) raindrop sizes between 1.25 and 3.5 mm scavenged mainly particle sizes between 70 and 250 nm. Lower scavenging was observed on particle sizes >300 nm, and particle sizes >600 nm were only scavenged by raindrop sizes >4.75 mm; iv) the respirable fraction before and after the rain events presented a statically significant decrease of -35%. The combination in this study of SMPS and disdrometer measurements has resulted in a more detailed characterization of the influence of this process on the submicrometer aerosol fraction, noting that below-cloud scavenging is one of the main removal pathways for submicrometer aerosol particles. This study thus contributes to improving the current state of knowledge of below-cloud scavenging.

Unusual winter Saharan dust intrusions at Northwest Spain: Air quality, radiative and health impacts.

Saharan air masses can transport high amounts of mineral dust particles and biological material to the Iberian Peninsula. During winter, this kind of events is not very frequent and usually does not reach the northwest of the Peninsula. However, between 21 and 22 February 2016 and between 22 and 23 February 2017, two exceptional events were registered in León (Spain), which severely affected air quality. An integrative approach including: i) typical synoptic conditions; ii) aerosol chemical composition; iii) particle size distributions; iv) pollen concentration; v) aerosol optical depth (AOD); vi) radiative forcing and vii) estimation of the impact of aerosols in the respiratory tract, was carried out. In the global characterization of these events, the exceedance of the PM10 daily limit value, an increase in the coarse mode and a rise in the iron concentration were observed. On the 2016 event, an AOD and extinction-related Ångström exponent clearly characteristic of desert aerosol (1.1 and 0.05, respectively) were registered. Furthermore, pollen grains not typical of flowering plants in this period were identified. The chemical analysis of the aerosol from the 2017 event allowed us to confirm the presence of the main elements associated with mineral sources (aluminum, calcium, and silica concentrations). An increase in the SO42-, NO3- and Cl- concentrations during the Saharan dust intrusion was also noted. However, in this event, there was no presence of atypical pollen types. The estimated dust radiative forcing traduced a cooling effect for surface and atmosphere during both events, corroborated by trends of radiative flux measurements. The estimated impact on the respiratory tract regions of the high levels of particulate matter during both Saharan dust intrusions showed high levels for the respirable fraction.

Outdoor and indoor particle characterization from a large and uncontrolled combustion of a tire landfill.

A large and uncontrolled fire of a tire landfill started in Seseña (Toledo, Spain) on May 13, 2016. An experimental deployment was immediately launched in the area for measuring regulated and non-standard air quality parameters to assess the potential impact of the plume at local and regional levels. Outdoor and indoor measurements of different parameters were carried out at a near school, approximately 700m downwind the burning tires. Real time measurements of ambient black carbon (BC) and total number particle concentrations were identified as good tracers of the smoke plume. Simultaneous peaks allowed us to characterize situations of the plume impact on the site. Outdoor total particle number concentrations reached in these occasions 3.8×105particlescm-3 (on a 10min resolution) whereas the indoor concentration was one order of magnitude lower. BC mass concentrations in ambient air were in the range of 2 to 7µgm-3, whereas concentrations<2µgm-3 were measured indoor. Indoor and outdoor deposited inhalable dust was sampled and chemically characterized. Both indoor and outdoor dust was enriched in tire components (Zn, sulfate) and PAHs associated to the tire combustion process. Infiltration processes have been documented for BC and particle number concentrations causing increases in indoor concentrations.

The influence of wildfires on aerosol size distributions in rural areas.

The number of particles and their size distributions were measured in a rural area, during the summer, using a PCASP-X. The aim was to study the influence of wildfires on particle size distributions. The comparative studies carried out reveal an average increase of around ten times in the number of particles in the fine mode, especially in sizes between 0.10 and 0.14 µm, where the increase is of nearly 20 times. An analysis carried out at three different points in time--before, during, and after the passing of the smoke plume from the wildfires--shows that the mean geometric diameter of the fine mode in the measurements affected by the fire is smaller than the one obtained in the measurements carried out immediately before and after (0.14 µm) and presents average values of 0.11 µm.