Does aerosol particulate matter attenuate UVA more as compared to UVB? I am trying to understand if winter aerosol particulate matter has a greater impact on UVB radiation as compared to UVA radiation. Would the attenuation be mainly due to scattering?
I am asking this question for latitudes less than 30 degrees north where UVB radiation is expected to reach ground even in winter.
 A: Firstly, a definition of what exactly is termed as particulate matter, according to the Australian Government Dept. of Environment and Energy page Particles. the are defined as being:

Airborne particles are sometimes referred to as 'particulate matter' or 'PM'. They include dust, dirt, soot, smoke, and liquid droplets. Some particles are large enough or dark enough to be seen as soot or smoke, while others are so small they can only be detected individually with a microscope

Particulate matter is further defined by their size (from the link above):

Particles can be classified on the basis of their size, referred to as
  their 'aerodynamic diameter'. 'Coarse particles' are those between 10
  and 2.5 micrometres (µm) in diameter; 'fine particles' are smaller
  than 2.5 µm; and 'ultrafine particles' are smaller than 0.1 µm. For
  comparison, the diameter of a human hair is 70 µm and this is seven
  times the diameter of the largest 'coarse particles'.

The classifications are often referred to as $PM_{10}$, $PM_{2.5}$ and $PM_{0.1}$ for 'course', 'fine' and 'ultrafine' particulate matter respectively.  Further classification can be made of the chemical toxicity etc - but that is beyond the scope of this answer.
The particulate matter species' sizes have been observed to be bimodal, as can be seen in the diagram from the Middle Tennessee State University (MTSU) webpage "Visibility and Light Scattering in the Atmosphere":

The point between the 2 peaks is approximately 2.5 µm
A comparison between the size fractions and other small entities is shown below, just to gain some perspective:

Image source: clinicalgate.com
Studying the effects of all aerosols, particularly particulate matter on incoming solar radiation has been of major interest to atmospheric sciences as it constitutes a major source of uncertainty in radiative models.  The research in how PM affects the UV (both UVA and UVB) has been, in part, a focus of many (like me) who are involved with photobiology.
There are several complications with PM, some species are emitted at a certain size, but due to chemical and other processes, they can grow into much larger secondary particulates. Additionally, some species have differing absorption of specific wavebands in the UV (and other wavelengths of light). So, this answer will concentrate on the size of the particles and their effect on the incoming UV radiation.
A key point made by the MTSU webpage (linked above) provides a general answer to one of your main questions ("Would the attenuation be mainly due to scattering?"):

Light scattering is caused by all atmospheric particles, but particles very near the same diameter as the wavelength of light scatter photons most effectively.

The MTSU webpage provides a comparison chart between electromagnetic radiation and some common types of aerosol/PM - of particular interest for this question is the solar radiation in the UV:

It is important to realise that scattering refers to light received by a particle and re-radiated at the same wavelength. 
This relates to the main part of your question, whether aerosol particulate matter attenuates more in the UVA than in the UVB - (essentially wavelengths of about 295 nm and above and divided at 315 or 320 nm depending on what reference you refer to (IARC Working Group Monograph - Solar and Ultraviolet Radiation)).
Essentially, a general answer is - it depends on the size of the particulate aerosol present.  The process is summarised nicely by the MTSU webpage as:

Particles larger than the wavelength of light can scatter light through three processes: (1) diffraction, (2) refraction, and (3) phase shift. Photons of light can also be absorbed by particles and converted to internal molecular energy. The efficiency with which a particle can scatter light and the direction in which the incident light is redistributed are dependent on all four of these effects.

The type of scattering is summarised in the diagram below (from Pennsylvania State University):

Mie Scattering

"Mie scattering" suggests situations where the size of the scattering particles is comparable to the wavelength of the light, rather than much smaller or much larger.

Ratyleigh Scattering

is the (dominantly) elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. 

The TL:DR of this is that, in general, UVB tends to be scattered by particulate matter more than UVA.  - As emphasised by the graph (from MTSU) below:

Absorption is also a major factor when it comes to attenuation of UV, particularly soot or 'black carbon' which is every present, not only in urban environments.  However, there are many species that absorb ultraviolet radiation - this is largely dependent on the properties of the PM species itself - but in general, absorption affects UVB more, as can be seen in the SCHIMACHY graph below:

Image Source: Global Aerosol Direct Effect Retrieval from Passive Hyperspectral Measurements
So summing all this up:
The amount of attenuation due to scattering and absorption of UV (UVA and UVB) by particulate matter depends on the amount. size and the type of particulate matter present AND the intensity of incoming UV radiation (seasons and cloud cover etc).  In general, UVB - which is already filtered by the atmosphere, is subjected to more scattering and absorption (depending on the PM species) than UVA.
