Ojalá no hubiera tanto polen en primavera, porque mi hermana acaba estornudando todo el día.

Ojalá introduces a wish, often one that feels difficult, unlikely, or contrary to reality.

In this sentence, Ojalá no hubiera tanto polen... means the speaker wishes the situation were different now: there is a lot of pollen, and the speaker wishes that were not true.

It is one of the most common ways to say I wish... in Spanish.

No. Ojalá can be followed directly by a verb:

• Ojalá no hubiera tanto polen
• Ojalá llueva mañana

You may also hear ojalá que, but in many cases the que is optional:

• Ojalá que no hubiera tanto polen

The version without que is completely natural.

Because after ojalá, Spanish often uses the subjunctive, and here the speaker is expressing an unreal or contrary-to-fact wish about the present.

• hay tanto polen = there is so much pollen
• ojalá no hubiera tanto polen = I wish there weren’t so much pollen

So hubiera is the imperfect subjunctive of haber, used here not to talk about the past, but to express an unreal present situation.

Not really. Even though hubiera is historically a past form, in this sentence it refers to a present unreal wish.

So:

• Ojalá no hubiera tanto polen = I wish there weren’t so much pollen now / in general

This is very common in Spanish: a past subjunctive form can express a present hypothetical or unreal idea.

Yes. Hubiera and hubiese are both correct imperfect subjunctive forms.

So these are both fine:

• Ojalá no hubiera tanto polen
• Ojalá no hubiese tanto polen

In everyday speech, hubiera is often more common, but both are standard.

Because this is the impersonal haber meaning there is / there are, and in standard Spanish that verb stays singular.

So Spanish says:

• hay mucho polen
• había muchas personas
• ojalá no hubiera tantos problemas

Even if the noun after it is plural, the verb with impersonal haber remains singular in careful standard Spanish.

Because tanto is used with nouns to express quantity, while tan is used with adjectives or adverbs.

Here polen is a noun, so you need tanto:

• tanto polen = so much pollen

Compare:

• tan alto = so tall
• tan rápido = so quickly

Also, polen is usually treated as an uncountable substance here, so tanto polen means so much pollen.

In Spanish, seasons often appear without the article after en when speaking generally:

• en primavera
• en verano
• en otoño
• en invierno

So en primavera simply means in spring in a general sense.

You may also hear en la primavera in some contexts, but en primavera is very natural and common.

Here acabar + gerundio means to end up doing something.

So:

• mi hermana acaba estornudando todo el día

means that, because of the pollen, the result is that she ends up sneezing all day.

It does not mean that she simply finishes sneezing. It means this is what ends up happening.

They are very different structures.

• acabar + gerundio = to end up doing something

  • acaba estornudando = she ends up sneezing

• acabar de + infinitive = to have just done something

  • acaba de estornudar = she has just sneezed

That small de changes the meaning completely.

Because the two parts are doing different jobs.

• Ojalá no hubiera tanto polen... expresses an unreal wish
• ...porque mi hermana acaba estornudando todo el día describes what actually happens

So the sentence combines:

1. a hypothetical wish about the situation
2. a present description of the real consequence

That tense combination is completely normal.

No, they are different.

• todo el día = all day
• todos los días = every day

In this sentence, todo el día describes the duration of the sneezing on a typical day when the pollen is bad.

So the idea is not necessarily that she sneezes every single day of the year, but that during spring, when this happens, she spends the whole day sneezing.

Yes, and the meaning is close, but the nuance changes.

• Ojalá no haya tanto polen... sounds more like a hope about the present or future, something still possible.
• Ojalá no hubiera tanto polen... sounds more like a less realistic wish, almost if only there weren’t so much pollen.

So both are possible, but hubiera makes the wish feel more contrary to the actual situation.

Yes, polen is masculine: el polen.

That is why you get:

• tanto polen

If the noun were feminine, you would use tanta:

• tanta agua
• tanta gente

Here tanto agrees in gender and number with polen, which is masculine singular.

Yes. It sounds natural and standard in Spain.

Some especially natural features are:

• Ojalá + imperfect subjunctive for an unreal wish
• en primavera for a general seasonal reference
• acabar + gerundio to mean end up doing

So for Spain Spanish, this sentence is perfectly normal and idiomatic.